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avr-libc Reference Manual

1. avrdude p 2313 e m flash i main hex avrdude AVR device initialized and ready to accept instructions avrdude Device signature 0xle9101 avrdude erasing chip avrdude done avrdude reading input file main hex avrdude input file main hex auto detected as Intel Hex avrdude writing flash 1749 0x00 avrdude 1750 bytes of flash written avrdude verifying flash memory against main hex avrdude reading on chip flash data 1749 0x00 avrdude verifying avrdude 1750 bytes of flash verified avrdude done Thank you The p 2313 option lets avrdude know that we are operating on an AT90S2313 chip This option specifies the device id and is matched up with the device of the same id in avrdude s configuration file usr local etc avrdude conf To list valid parts specify the v option The e option instructs avrdude to perform a chip erase before programming this is almost always necessary before programming the flash The m flash option indicates that we want to upload data into the flash memory while i main hex specifies the name of the input file The EEPROM is uploaded in the same way the only difference is that you would use m eeprom instead of m flash To use interactive mode use the t option avrdude p 2313 t Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 171 avrdude AVR device initialized and ready to accept instructions avrdude D
2. All the people who currently maintain the tools and or have submitted sugges tions patches and bug reports See the AUTHORS files of the various tools And lastly all the users who use the software If nobody used the software we would probably not be very motivated to continue to develop it Keep those bug reports coming 7 2 avr libc and assembler programs 72 1 Introduction There might be several reasons to write code for AVR microcontrollers using plain assembler source code Among them are Code for devices that do not have RAM and are thus not supported by the C compiler Code for very time critical applications Special tweaks that cannot be done in C Usually all but the first could probably be done easily using the inline assembler facility of the compiler Although avr libc is primarily targeted to support programming AVR microcontrollers using the C and C language there s limited support for direct assembler usage as well The benefits of it are Use of the C preprocessor and thus the ability to use the same symbolic constants that are available to C programs as well as a flexible macro concept that can use any valid C identifier as a macro whereas the assembler s macro concept is basically targeted to use a macro in place of an assembler instruction Use of the runtime framework like automatically assigning interrupt vectors For devices that have RAM initializing the RAM variables can also
3. Define _SFR_ASM_COMPAT as 1 to make these names work as simple constants ad dresses of the I O registers This is necessary when included in preprocessed assem bler x S source files so it is done automatically if __ ASSEMBLER__ is defined By default all addresses are defined as if they were memory addresses used in lds sts instructions To use these addresses in in out instructions you must subtract 0x20 from them For more backwards compatibility insert the following at the start of your old assem bler source file define __SFR_OFFSET 0 This automatically subtracts 0x20 from I O space addresses but it s a hack so it is recommended to change your source wrap such addresses in macros defined here as shown below After this is done the ___SF R_OFF SET definition is no longer necessary and can be removed Real example this code could be used in a boot loader that is portable between devices with SPMCR at different addresses lt avr iom163 h gt define SPMCR _SFR_IO8 0x37 lt avr iom128 h gt define SPMCR _SFR_MEM8 0x68 if _SFR_IO_REG_P SPMCR out _SFR_IO_ADDR SPMCR r24 else sts _SFR_MEM_ADDR SPMCR r24 endif Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 9 Power Management and Sleep Modes 27 You can use the in out cbi sbi sbic sbis instructions without the_ SFR_ IO_REG_P test if you know that the register is in the I O space as with SREG for exa
4. Note 12 This is called master receiver mode the bus master still supplies the SCL clock but the device slave drives the SDA line with the appropriate data After 8 data bits the master responds with an ACK bit SDA driven low in order to request another data transfer from the slave or it can leave the SDA line high NACK indicating to the slave that it is going to stop the transfer now Assertion of ACK is handled by setting the TWEA bit in TWCR when starting the current transfer Note 13 The control word sent out in order to initiate the transfer of the next data packet is initially set up to assert the TWEA bit During the last loop iteration TWEA is de asserted so the client will get informed that no further transfer is desired Note 14 Except in the case of lost arbitration all bus transactions must properly be terminated by the master initiating a stop condition Note 15 Writing to the EEPROM device is simpler than reading since only a master transmitter mode transfer is needed Note that the first packet after the SLA W selection is always considered to be the EEPROM address for the next operation This packet is exactly the same as the one above sent before starting to read the device In case a master transmitter mode transfer is going to send more than one data packet all following packets will be considered data bytes to write at the indicated address The internal address pointer will be incremented afte
5. Output a cross reference table to the map file in case Map is also present or to stdout e section start sectionname org Start section sectionname at absolute address org e Tbss org e Tdata org e Ttext org Start the bss data or text section at org respectively e T scriptfile Use scriptfile as the linker script replacing the default linker script De fault linker scripts are stored in a system specific location e g under usr local avr lib ldscripts on Unix systems and consist of the AVR architecture name avr2 through avr5 with the suffix x appended They describe how the various memory sections will be linked together 7 10 3 2 Passing linker options from the C compiler By default all unknown non option arguments on the avr gcc command line 1 e all filename arguments that don t have a suffix that is handled by avr gcc are passed straight to the linker Thus all files ending in o object files and a object libraries are provided to the linker System libraries are usually not passed by their explicit filename but rather using the 1 option which uses an abbreviated form of the archive filename see above avr libe ships two system libraries libc a and libm a While the standard library libc a will always be searched for unresolved references when the linker is started using the C compiler frontend i e there s always at least one implied 1c option the mathematics library 1ibm
6. atmega323 atmega325 atmega3250 atmega48 atmega64 atmega645 atmega6450 atmega8515 atmega8535 atmega88 ATtiny Type Devices e attiny11 1 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 2 avr libc Module Index 4 attiny12 1 attiny 13 attiny15 1 attiny22 attiny26 attiny28 1 attiny2313 Misc Devices at94K 2 at76c711 3 at43usb320 at43usb355 at86rf401 Note 1 Assembly only There is no direct support for these devices to be programmed in C since they do not have a RAM based stack Still it could be possible to program them in C see the FAQ for an option Note 2 The at94K devices are a combination of FPGA and AVR microcontroller TRoth 2002 11 12 Not sure of the level of support for these More information would be welcomed Note 3 The at76c711 is a USB to fast serial interface bridge chip using an AVR core 2 avr libc Module Index 2 1 avr libc Modules Here is a list of all modules Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 2 1 avr libc Modules 5 Bootloader Support Utilities 7 CRC Computations 11 Busy wait delay loops 13 EEPROM handling 15 AVR device specific IO definitions 17 Parity bit generation 18 Program Space String Utilities 19 Power Management and Sleep Modes 27 Watchdog timer handling 28 Character Operations 30 System Errors errno 32 Integer Type conversions 33 Mathematics 33 Se
7. e typedef int int16_t e typedef unsigned int uint16_t 32 bit types e typedef long int32_t e typedef unsigned long uint32_t 64 bit types e typedef long long int64_t e typedef unsigned long long uint64_t Pointer types These allow you to declare variables of the same size as a pointer e typedef int16_t intptr_t e typedef uint16_t uintptr_t Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 16 Standard Integer Types 41 5 16 2 Typedef Documentation 5 16 2 1 typedef int int16_t 16 bit signed type 5 16 2 2 typedef long int32_t 32 bit signed type 5 16 2 3 typedef long long int64_t 64 bit signed type 5 16 2 4 typedef signed char int8_t 8 bit signed type 5 16 2 5 typedef int16_t intptr_t Signed pointer compatible type 5 16 2 6 typedef unsigned int uint16_t 16 bit unsigned type 5 16 2 7 typedef unsigned long uint32_t 32 bit unsigned type 5 16 2 8 typedef unsigned long long uint64_t 64 bit unsigned type 5 16 2 9 typedef unsigned char uint8_t 8 bit unsigned type 5 16 2 10 typedef uint16_t uintptr_t Unsigned pointer compatible type Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 42 5 17 Standard IO facilities 5 17 1 Detailed Description include lt stdio h gt Warning This implementation of the standard IO facilities is new to avr libc It is not yet expected to remain stable so some aspects of the API might
8. Compatibility defines This should work on ATmega8 ATmegal6 ATmegal63 ATmega323 and ATmegal28 IOW on all devices that provide a builtin TWI interface On the 128 it defaults to USART 1 ifndef UCSRB ifdef UCSRIA ATmegal28 define UCSRA UCSRIA define UCSRB UCSRIB define UBRR UBRRIL define UDR UDRI else ATmega8 define UCSRA USR define UCSRB UCR endif endif ifndef UBRR define UBRR UBRRL endif Note 3 TWI address for 24Cxx EEPROM 1010 E2 El EO R W 24C01 24C02 1 0 1 0 E2 El A8 R W 24C04 1 0 1 0 E2 A9 A8 R W 24C08 1 0 1 0 A10 A9 A8 R W 24C16 ky define TWI_SLA_24CXX 0xa0 E2 El EO 0 0 0 Maximal number of iterations to wait for a device to respond for a selection Should be large enough to allow for a pending write to complete but low enough to properly abort an infinite loop in case a slave is broken or not present at all With 100 kHz TWI clock transfering the start condition and SLA R W packet takes about 10 ts The longest write period is supposed to not exceed 10 ms Thus normal operation should not require more than 100 iterations to get the device to respond to a selection DVA define MAX_ITER 200 Number of bytes that can be written in a row see comments for ee24xx_write_page below Some vendor s devices would accept 16 but 8 seems to be the lowest common denominator O
9. The strtok_r function returns a pointer to the next token or NULL when no more tokens are found 5 19 2 26 char x strupr char x string Convert a string to upper case Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 20 Interrupts and Signals 76 The strupr function will convert a string to upper case Only the lower case alphabetic characters a z are converted Non alphabetic characters will not be changed Returns The strupr function returns a pointer to the converted string The pointer is the same as that passed in since the operation is perform in place 5 20 Interrupts and Signals 5 20 1 Detailed Description Note This discussion of interrupts and signals was taken from Rich Neswold s docu ment See Acknowledgments It s nearly impossible to find compilers that agree on how to handle interrupt code Since the C language tries to stay away from machine dependent details each compiler writer is forced to design their method of support In the AVR GCC environment the vector table is predefined to point to interrupt rou tines with predetermined names By using the appropriate name your routine will be called when the corresponding interrupt occurs The device library provides a set of default interrupt routines which will get used if you don t define your own Patching into the vector table is only one part of the problem The compiler uses by convention a set of registers when
10. There is still a risk that the heap and stack could collide if there are large requirements for either dynamic memory or stack space The former can even happen 1f the allocations aren t all that large but dynamic memory allocations get fragmented over time such that new requests don t quite fit into the holes of previously freed regions Large stack space requirements can arise in a C function containing large and or numerous local variables or when recursively calling function Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 5 Using malloc 151 Note The pictures shown in this document represent typical situations where the RAM locations refer to an ATmega128 The memory addresses used are not displayed in a linear scale on board RAM 0x0100 Ox10FF 0x1100 OxFFFF external RAM j gt SP RAMEND brkval lt SP __malloc_margin gt __malloc_heap_start __heap_start L _ bss end __data_end __bss_start data start Figure 2 RAM map of a device with internal RAM Finally there s a challenge to make the memory allocator simple enough so the code size requirements will remain low yet powerful enough to avoid unnecessary memory fragmentation and to get it all done with reasonably few CPU cycles since microcon trollers aren t only often low on space but also run at much lower speeds than the typical PC these days The memory allocator implemented in avr libc tries to
11. avr_pgmspace 20 pgm_read_word avr_pgmspace 20 pgm_read_word_far avr_pgmspace 21 pgm_read_word_near avr_pgmspace 21 PGM_VOID_P avr_pgmspace 21 pow avr_math 36 Power Management and Sleep Modes 26 printf avr_stdio 48 printf_P avr_stdio 48 Program Space String Utilities 18 PSTR avr_pgmspace 21 putc avr_stdio 44 putchar avr_stdio 44 puts avr_stdio 48 puts_P Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen INDEX 188 avr_stdio 48 qsort avr_stdlib 62 quot div_t 109 Idiv_t 109 rand avr_stdlib 62 RAND_MAX avr_stdlib 57 rand_r avr_stdlib 62 random avr_stdlib 63 RANDOM_MAX avr_stdlib 57 random_r avr_stdlib 63 realloc avr_stdlib 63 rem div_t 109 Idiv_t 109 scanf avr_stdio 48 scanf_P avr_stdio 48 sel avr_interrupts 79 set_sleep_mode avr_sleep 26 setjmp longjmp 38 setjmp 38 Setjmp and Longjmp 37 SIGNAL avr_interrupts 79 sin avr_math 36 sinh avr_math 36 sleep_mode avr_sleep 26 snprintf avr_stdio 48 snprintf_P avr_stdio 48 Special function registers 80 sprintf avr_stdio 49 sprintf_P avr_stdio 49 sqrt avr_math 36 square avr_math 36 srand avr_stdlib 63 srandom avr_stdlib 63 sscanf avr_stdio 49 sscanf_P avr_stdio 49 Standard Integer Types 39 Standard IO facilities 41 stderr avr_stdio 44 stdin avr_stdio 45 stdout avr_stdio 45 strcasecmp avr_string 69 strcase
12. sembler environment that uses relocatable object files as it is the linker that determines the final position of some object in ROM or RAM Along with the architecture independent standard operators there are some AVR specific operators available which are unfortunately not yet described in the official documentation The most notable operators are 108 Takes the least significant 8 bits of a 16 bit integer e hi8 Takes the most significant 8 bits of a 16 bit integer pm Takes a program memory ROM address and converts it into a RAM ad dress This implies a division by 2 as the AVR handles ROM addresses as 16 bit words e g in an IJMP or ICALL instruction and can also handle relocatable symbols on the right hand side Example ldi r24 108 pm somefunc ldi r25 hi8 pm somefunc call something This passes the address of function somefunc as the first parameter to function something Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 118 7 3 0 0 gt uo r o 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Frequently Asked Questions FAQ Index My program doesn t recognize a variable updated within an interrupt routine I get undefined reference to for functions like sin How to permanently bind a variable to a register How to modify MCUCR or WDTCR early What is all this _BVO stuff about Can I u
13. 7 8 6 UISP Uisp also uses the configure system so to build and install gunzip c uisp lt version gt tar gz tar xf cd uisp lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install UY UN 117 17 UN 147 Ur Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 8 Installing the GNU Tool Chain 168 7 8 7 Avrdude Note It has been ported to windows via cygwin and linux Other unix systems should be trivial to port to avrdude is part of the FreeBSD ports system To install it simply do the following cd usr ports devel avrdude make install Note Installation into the default location usually requires root permissions However running the program only requires access permissions to the appropriate ppi 4 device Building and installing on other systems should use the configure system as such gunzip c avrdude lt version gt tar gz tar xf cd avrdude lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install UN UU 147 17 E MN Ur 7 8 8 GDB for the AVR target Gdb also uses the configure system so to build and install bunzip2 c gdb lt version gt tar bz2 tar xf cd gdb lt version gt mkdir obj avr cd obj avr configure prefix SPREFIX target avr make make install UN 17 UU UN 147 47 Ue Note If you are planning on using avr gdb you will probably want to install either simulavr or av
14. Note that malloc does not initialize the returned memory to zero bytes See the chapter about malloc usage for implementation details 5 18 4 18 void qsort void __base size_t __nmemb size_t __size _ compar_ fn_t__ compar The qsort function is a modified partition exchange sort or quicksort The qsort function sorts an array of nmemb objects the initial member of which is pointed to by base The size of each object is specified by size The contents of the array base are sorted in ascending order according to a comparison function pointed to by compar which requires two arguments pointing to the objects being compared The comparison function must return an integer less than equal to or greater than zero 1f the first argument is considered to be respectively less than equal to or greater than the second 5 18 4 19 int rand void The rand function computes a sequence of pseudo random integers in the range of 0 to RAND_MAX as defined by the header file lt stdlib h gt The srand function sets its argument seed as the seed for a new sequence of pseudo random numbers to be returned by rand These sequences are repeatable by calling srand with the same seed value If no seed value is provided the functions are automatically seeded with a value of 1 In compliance with the C standard these functions operate on int arguments Since the underlying algorithm already uses 32 bit calculations this causes
15. The general form is asm code output operand list input operand list clobber list In the code section operands are referenced by a percent sign followed by a single digit O refers to the first 1 to the second operand and so forth From the above example O refers to r value and 1 refers to I _SFR_IO_ADDR PORTD This may still look a little odd now but the syntax of an operand list will be explained soon Let us first examine the part of a compiler listing which may have been generated from our example Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 140 lds r24 value APP in 224 12 NOAPP sts value r24 The comments have been added by the compiler to inform the assembler that the in cluded code was not generated by the compilation of C statements but by inline as sembler statements The compiler selected register r24 for storage of the value read from PORTD The compiler could have selected any other register though It may not explicitely load or store the value and it may even decide not to include your assembler code at all All these decisions are part of the compiler s optimization strategy For example if you never use the variable value in the remaining part of the C program the compiler will most likely remove your code unless you switched off optimization To avoid this you can add the volatile attribute to the asm statement asm volatile in
16. This is what the constant fuzz is for Note 5 External functions need to be declared to be global main is the application entry point that will be jumped to from the ininitalization routine in crt s1200 0 Note 6 The main loop is just a single jump back to itself Square wave generation itself is completely handled by the timer 0 overflow interrupt service A sleep instruction using idle mode could be used as well but probably would not conserve much energy anyway since the interrupt service is executed quite frequently Note 7 Interrupt functions can get the usual names that are also available to C programs The linker will then put them into the appropriate interrupt vector slots Note that they must be declared global in order to be acceptable for this purpose This will only work if lt avr io h gt has been included Note that the assembler or linker have no chance to check the correct spelling of an interrupt function so it should be double checked When analyzing the resulting object file using avr objdump or avr nm a name like __vector_N should appear with N being a small integer number Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 2 avr libc and assembler programs 116 Note 8 As explained in the section about special function registers the actual IO port address should be obtained using the macro _SFR_IO_ADDR The AT90S1200 does not have RAM thus the memory mapped approach to ac
17. every AVR device has a different interrupt vector table so some signals might not be available Check the data sheet for the device you are using FIXME Fill in the blanks Gotta read those durn data sheets Note The SIGNAL and INTERRUPTO macros currently cannot spell check the argu ment passed to them Thus by misspelling one of the names below in a call to SIGNAL or INTERRUPTO a function will be created that while possibly being usable as an interrupt function is not actually wired into the interrupt vector table No warning will be given about this situation Signal Name Description SIG_2WIRE_SERIAL 2 wire serial interface aka T178C tm SIG_ADC ADC Conversion complete SIG_COMPARATOR Analog Comparator Interrupt SIG_EEPROM_READY Eeprom ready SIG_FPGA_INTERRUPTO SIG_FPGA_INTERRUPT1 SIG_FPGA_INTERRUPT2 SIG_FPGA_INTERRUPT3 SIG_FPGA_INTERRUPT4 SIG_FPGA_INTERRUPTS SIG_FPGA_INTERRUPT6 SIG_FPGA_INTERRUPT7 SIG_FPGA_INTERRUPT8 SIG_FPGA_INTERRUPT9 SIG_FPGA_INTERRUPT10 SIG_FPGA_INTERRUPT11 SIG_FPGA_INTERRUPT12 SIG_FPGA_INTERRUPT13 SIG_FPGA_INTERRUPT14 SIG_FPGA_INTERRUPT15 SIG_INPUT_CAPTURE1 Input Capture Interrupt SIG_INPUT_CAPTURE3 Input Capture3 Interrupt SIG_INTERRUPTO External Interrupt0 SIG_INTERRUPT1 External Interrupt SIG_INTERRUPT2 External Interrupt2 SIG_INTERRUPT3 External Interrupt3 SIG_INTERRUPT4 External
18. function returns a pointer to the matching byte or NULL if the character does not occur in the given memory area 5 19 2 3 int memcmp const void x s1 const void x s2 size_t len Compare memory areas The memcmp function compares the first len bytes of the memory areas sl and s2 The comparision is performed using unsigned char operations Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 70 Returns The memcmp function returns an integer less than equal to or greater than zero if the first len bytes of s1 is found respectively to be less than to match or be greater than the first len bytes of s2 Note Be sure to store the result in a 16 bit variable since you may get incorrect results if you use an unsigned char or char due to truncation Warning This function is not mint8 compatible although if you only care about testing for equality this function should be safe to use 5 19 2 4 void x memcpy void dest const void x src size_t len Copy a memory area The memcpy function copies len bytes from memory area src to memory area dest The memory areas may not overlap Use memmove if the memory areas do overlap Returns The memcpy function returns a pointer to dest 5 19 2 5 void x memmove void dest const void src size_t len Copy memory area The memmove function copies len bytes from memory area src to memory area dest The memory areas may overlap Return
19. int32_t avr_stdint 40 int64_t avr_stdint 40 int8_t avr_stdint 40 Integer Type conversions 32 INTERRUPT avr_interrupts 79 Interrupts and Signals 75 intptr_t avr_stdint 40 inverse avr_math 35 isalnum ctype 30 isalpha ctype 30 isascii ctype 30 isblank ctype 30 iscntrl ctype 30 isdigit ctype 30 isgraph ctype 30 isinf avr_math 35 islower ctype 30 isnan avr_math 35 isprint ctype 30 ispunct ctype 31 isspace ctype 31 isupper ctype 31 isxdigit ctype 31 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen INDEX 187 itoa avr_stdlib 60 labs avr_stdlib 61 Idexp avr_math 35 Idiv avr_stdlib 61 Idiv_t 109 quot 109 rem 109 log avr_math 35 log10 avr_math 36 longjmp setimp 38 loop_until_bit_is_clear avr_sfr 82 loop_until_bit_is_set avr_sfr 82 Itoa avr_stdlib 61 M_PI avr_math 33 M_SQRT2 avr_math 33 malloc avr_stdlib 62 Mathematics 32 memccpy avr_string 68 memchr avr_string 68 memcmp avr_string 68 memcpy avr_string 69 memcpy_P avr_pgmspace 21 memmove avr_string 69 memset avr_string 69 modf avr_math 36 Parity bit generation 17 parity_even_bit avr_parity 17 PGM_P avr_pgmspace 19 pgm_read_byte avr_pgmspace 19 pgm_read_byte_far avr_pgmspace 19 pgm_read_byte_near avr_pgmspace 20 pgm_read_dword avr_pgmspace 20 pgm_read_dword_far avr_pgmspace 20 pgm_read_dword_near
20. loop forever the interrupts are doing the rest for Note 6 La return 0 b6 84 e0 ldi r24 0x04 4 b8 89 bf out 0x39 r24 57 ba 78 94 sei be 08 93 ret 000000be lt main gt be cf ed Let 228 U2Dr y 223 c0 dO el Tdi r29 0x00 O c2 de bf out 0x3e r29 62 c4 cd bf out 0x3d r28 61 c6 ef af rcall 34 Oxa6 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 92 gor CE timp 2 Oxc8 000000ca lt __bad_interrupt gt ca 9a cf rjmp 204 0x0 5 23 5 Linker Map Files avr objdump is very useful but sometimes it s necessary to see information about the link that can only be generated by the linker A map file contains this information A map file is useful for monitoring the sizes of your code and data It also shows where modules are loaded and which modules were loaded from libraries It is yet another view of your application To get a map file I usually add Wl Map demo map to my link command Relink the application using the following command to generate demo map a portion of which is shown below avr gcc g mmcu at90s2313 Wl Map demo map o demo elf demo o Some points of interest in the demo map file are rela plt rela plt text 0x00000000 Oxce vectors vectors 0x00000000 0x16 build crt1 crts2313 0 0x00000000 _ vectors 0x00000000 _ vector_default 0x00000016 _ ctors_start The text segmen
21. method is described how such constant data can be moved out to flash ROM How ever a constant string located in flash ROM is no longer a valid argument to pass to a function that expects a const char x type string since the AVR processor needs the special instruction LPM to access these strings Thus separate functions are needed that take this into account Many of the standard C library functions have equivalents available where one of the string arguments can be located in flash ROM Private func tions in the applications need to handle this too For example the following can be used to implement simple debugging messages that will be sent through a UART include lt inttypes h gt include lt avr io h gt include lt avr pgmspace h gt int uart_putchar char c if c An uart_putchar r loop_until_bit_is_set USR UDRE UDR c return 0 so it could be used for fdevopen too void debug_P const char addr ghar o while c pgm_read_byte addr uart_putchar c int main void Loinit initialize UART e debug_P PSTR foo was here n return 0 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 135 Note By convention the suffix _P to the function name is used as an indication that this function is going to accept a program space string Note also the use of the PSTR macro Back to FAQ
22. tunable 5 18 5 3 charx __malloc_heap_end malloc tunable 5 18 5 4 charx __malloc_heap_start malloc tunable 5 18 5 5 charx __malloc_heap_start amp __heap_start malloc tunable Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 5 18 5 6 charx __malloc_heap_start malloc tunable 5 18 5 7 size_t__malloc_margin malloc tunable 5 18 5 8 size_t__malloc_margin 32 malloc tunable 5 18 5 9 size_t ___ malloc_margin malloc tunable 5 19 Strings 5 19 1 Detailed Description include lt string h gt The string functions perform string operations on NULL terminated strings Note If the strings you are working on resident in program space flash you will need to use the string functions described in Program Space String Utilities Functions void memccpy void const void x int size_t void x memchr const void x int size_t _ ATTR_ PURE int memcmp const void const void x size_t __ ATTR_PURE void x memcpy void const void size_t void x memmove void x const void x size_t void x memset void x int size_t int strcasecmp const char x const char __ ATTR_PURE char x strcat char x const char char x strchr const char x int __ATTR_PURE int stremp const char x const char x __ ATTR_PURE char x strcpy char x const char x size_t strlcat char x const char x size_t size_t strlcpy char const char siz
23. 0 1 r value I _SFR_IO_ADDR PORTD The last part of the asm instruction the clobber list is mainly used to tell the compiler about modifications done by the assembler code This part may be omitted all other parts are required but may be left empty If your assembler routine won t use any input or output operand two colons must still follow the assembler code string A good example is a simple statement to disable interrupts asm volatile cli 7 4 2 Assembler Code You can use the same assembler instruction mnemonics as you d use with any other AVR assembler And you can write as many assembler statements into one code string as you like and your flash memory is able to hold Note The available assembler directives vary from one assembler to another To make it more readable you should put each statement on a seperate line asm volatile nop n t nop n t nop n t nop n t DD The linefeed and tab characters will make the assembler listing generated by the com piler more readable It may look a bit odd for the first time but that s the way the compiler creates it s own assembler code Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 141 You may also make use of some special registers Symbol Register _ SREG__ Status register at address 0x3F _ SP_H__ Stack pointer high byte at address 0x3E SP Stack pointer low byte at address 0x3D
24. 2005 for avr libc by Doxygen 7 10 Using the GNU tools 173 Architecture MCU name Macro avr3 at43usb320 _ AVR_AT43USB320__ avr3 at43usb355 _ AVR_AT43USB355__ avr3 at76c711 __AVR_AT76C711__ avr4 atmega48 __AVR_ATmega48__ avr4 atmega8 _ AVR_ATmega8__ avr4 atmega8515 _ AVR_ATmega8515__ avr4 atmega8535 _ AVR_ATmega8535__ avr4 atmega88 __AVR_ATmega88__ avr5 at90can128 _ AVR_AT9OCAN128__ avr5 atmega 128 __AVR_ATmegal28__ avr5 atmega16 __AVR_ATmegal6__ avr5 atmegal61 __AVR_ATmegal61__ avr5 atmegal62 _ AVR_ATmegal62__ avr5 atmega 163 __AVR_ATmegal63__ avr5 atmega 165 __AVR_ATmegal65__ avr5 atmega 168 __AVR_ATmegal68__ avr5 atmegal69 _AVR_ATmegal69__ avr5 atmega32 __AVR_ATmega32__ avr5 atmega323 __AVR_ATmega323__ avr5 atmega325 __AVR_ATmega325__ avr5 atmega3250 _ AVR_ATmega3250__ avr5 atmega64 _ AVR_ATmega64__ avr5 atmega645 __AVR_ATmega645__ avr5 atmega6450 _ AVR_ATmega6450__ avr5 at94k AVR_AT94K e morder1 e morder2 Change the order of register assignment The default is 124 r25 r18 r19 120 r21 r22 r23 r30 r31 r26 r27 r28 r29 r17 r16 r15 r14 r13 r12 r11 r10 19 r8 r7 r6 r5 r4 r3 r2 r0 r1 Order 1 uses r18 r19 r20 r21 r22 r23 r24 r25 r30 r31 r26 r27 r28 r29 r17 r16 r15 r14 r13 r12 r11 r10 r9 r8 r7 r6 r5 r4 r3 r2 r0 rl Order 2 uses 125 r24 r23 r
25. 25 OXO0 0 118 Oe 94 7c 00 call Oxf8 You can clearly see that 0x0038 is correctly passed for the address of the io port Looking at the disassembled object code for the body of the function we can see that the function is indeed performing the operation we intended void set_bits_func_correct volatile uint8_t port uint8_t mask f8 fc 01 movw r30 r24 port mask fa 80 81 ld r24 Z Lo 86 2b or r24 r22 fe 80 83 st Z r24 100 08 95 ret Notice that we are accessing the io port via the LD and ST instructions The port parameter must be volatile to avoid a compiler warning Note Because of the nature of the IN and OUT assembly instructions they can not be used inside the function when passing the port in this way Readers interested in the details should consult the Instruction Set data sheet Finally we come to the macro version of the operation In this contrived example the macro is the most efficient method with respect to both execution speed and code size set_bits_macro PORTB Oxf0 Lies 88 b3 in r24 0x18 24 lle 80 6f ori r24 OxFO 240 120 88 bb out 0x18 r24 24 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 128 Of course in a real application you might be doing a lot more in your function which uses a passed by reference io port address and thus the use of a function over a macro could save you some code space but still at a cost of
26. 7 3 Frequently Asked Questions 133 Back to FAQ Index 7 3 18 How do I relocate code to a fixed address First the code should be put into a new named section This is done with a section attribute _attribute__ section bootloader In this example bootloader is the name of the new section This attribute needs to be placed after the prototype of any function to force the function into the new section void boot void __attribute__ section bootloader To relocate the section to a fixed address the linker flag section start is used This option can be passed to the linker using the W1 compiler option Wl section start bootloader 0x1E000 The name after section start is the name of the section to be relocated The number after the section name is the beginning address of the named section Back to FAQ Index 7 3 19 My UART is generating nonsense My ATmega128 keeps crashing Port F is completely broken Well certain odd problems arise out of the situation that the AVR devices as shipped by Atmel often come with a default fuse bit configuration that doesn t match the user s expectations Here is a list of things to care for All devices that have an internal RC oscillator ship with the fuse enabled that causes the device to run off this oscillator instead of an external crystal This often remains unnoticed until the first attempt is made to use something critical in timing like UART commun
27. 7 4 7 C Names Used in Assembler Code By default AVR GCC uses the same symbolic names of functions or variables in C and assembler code You can specify a different name for the assembler code by using a special form of the asm statement unsigned long value asm clock 3686400 This statement instructs the compiler to use the symbol name clock rather than value This makes sense only for external or static variables because local variables do not have symbolic names in the assembler code However local variables may be held in registers With AVR GCC you can specify the use of a specific register void Count void register unsigned char counter asm r3 some code asm volatile clr r3 more code The assembler instruction clr r3 will clear the variable counter AVR GCC will not completely reserve the specified register If the optimizer recognizes that the vari able will not be referenced any longer the register may be re used But the compiler Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 5 Using malloc 150 is not able to check wether this register usage conflicts with any predefined register If you reserve too many registers in this way the compiler may even run out of registers during code generation In order to change the name of a function you need a prototype declaration because the compiler will not accept the asm keyword in the function definition extern long C
28. 7 8 Using Sections in Assembler Code 162 29 Using Sections ine Code rcs ee ee ee ea RSS 162 7 8 Installing the GNU Tool Chain 0 163 781 Required Tools lt s sc chap css Sea ad So 164 232 Opiomal Tods ze 164 7 8 3 GNU Binutils for the AVR target 165 384 GCC forthe AVR target 00 ee 6 166 TAS AVR DIDS ooo Giba ee ew ana A 167 Yr Smib ee Bk e 167 re xi ke e 168 7 8 8 GDB forthe AVR target o 168 rr BRE 11 A amp Ace eee ee Swedes Beg 168 rz AYRES eee 169 7 9 Using the avrdude program 169 1 10 Using the GNU tools eRe o 171 7 10 1 Options for the C compiler avr gcc 0 0 0 171 7 10 2 Options for the assembler avr as 176 7 10 3 Controlling the linker aveld 178 OLI Tda LIE seger ee OS od tla Eee SRR 6 180 1 AVR Libc The latest version of this document is always available from http savannah nongnu org projects avr libc Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 1 1 Supported Devices 2 The AVR Libc package provides a subset of the standard C library for Atmel AVR 8 bit RISC microcontrollers In addition the library provides the basic startup code needed by most applications There is a wealth of information in this document which goes beyond simply describ ing the interfaces and routines provided by the library We hope that this document provides enough information t
29. AVR controller series It should be kept in mind that these de mos serve mainly educational purposes and are normally not directly suitable for use in any production environment Usually they have been kept as simple as sufficient to demonstrate one particular feature Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 84 The simple project is somewhat like the Hello world application for a microcon troller about the most simple project that can be done It is explained in good detail to allow the reader to understand the basic concepts behind using the tools on an AVR microcontroller The Example using the two wire interface TWT project explains the use of the two wire hardware interface also known as I2C that is present on many AVR controllers Modules e groupA simple project e groupExample using the two wire interface TWI 5 23 A simple project At this point you should have the GNU tools configured built and installed on your system In this chapter we present a simple example of using the GNU tools in an AVR project After reading this chapter you should have a better feel as to how the tools are used and how a Makefile can be configured 5 23 1 The Project This project will use the pulse width modulator PWM to ramp an LED on and off every two seconds An AT90S2313 processor will be used as the controller The circuit for this demonstration is shown in the schemati
30. Chain 163 void my_init_portb void outb PORTB Oxff outb DDRB Oxff 7 8 Installing the GNU Tool Chain Note This discussion was taken directly from Rich Neswold s document See Acknowl edgments This discussion is Unix specific FIXME troth 2002 08 13 we need a volunteer to add windows specific notes to these instructions This chapter shows how to build and install a complete development environment for the AVR processors using the GNU toolset The default behaviour for most of these tools is to install every thing under the usr local directory In order to keep the AVR tools separate from the base system it is usually better to install everything into usr local avr If the usr local avr directory does not exist you should create it before trying to install anything You will need root access to install there If you don t have root access to the system you can alternatively install in your home directory for exam ple in SHOME local avr Where you install is a completely arbitrary decision but should be consistent for all the tools You specify the installation directory by using the prefix dir option with the configure script It is important to install all the AVR tools in the same directory or some of the tools will not work correctly To ensure consistency and simplify the discussion we will use SPREF IX to refer to whatever directory you wish to install in You can set this as an
31. Controls a LED that can be directly connected from OC1 OC1A to GND The brightness of the LED is controlled with the PWM After each period of the PWM the PWM value is either incremented or decremented that s all SId demo c v 1 4 2004 07 21 21 03 07 joerg_wunsch Exp clude lt inttypes h gt clude lt avr io h gt clude lt avr interrupt h gt clude lt avr signal h gt if defined __AVR_AT90S2313__ 10 10 10 ba H H oO HE onaQaaQaaaar raaddcieaaradaiaaaaradda Se de de de de de SE de SE SE SE OSE SE OSE OSE 4 GE SE OSE SE SE EE oO a Q fine OC1 PB3 fine OCR OCR1 fine DDROC DD defined __AV ine OC1 PB1 ine DDROC DD ine OCR OCR1 defined __AV defined __AV defined __AV fine OC1 PD5 fine DDROC DD Fh FH Fh d d d i d d d i defined __AV fine OCR OCRIA RB R_AT90S2333__ RB R_AT90S4414_ R_AT90S4434__ R_ATmegal63__ RD R_ATmega8__ OC1 PB1 DDROC DD fine fine ine fine fine defined __AV fine OC1 PD5 fine DDROC DD fine fine fine defined __AV fine OC1 PB5 fine DDROC DD fine fine fine h H efined COM11 OCR OCRIA PWM10 WGM10 PWM11 WGM11 OCR OCRIA PWM10 WGM10 PWM11 WGM11 RB R_ATmega32__ RD R_ATmega64__ RB OCR OCRIA PWM10 WGM10 PWM11 WGM11 fine XCOM11 COM11 defined COM1A1 fine XCOM11 COM1A1 defined __AVR_AT90S4433__ defined __AVR_AT90S8515__ defined __AVR_AT90S8535__ defined __AVR_ATmeg
32. Note 16 _BV TWEN send stop condition Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 105 Wrapper around ee24xx_write_page that repeats calling this function until either an error has been returned or all bytes have been written Ey int ee24xx_write_bytes uint16_t eeaddr int len uint8_t buf int rv total total 0 do if DEBUG printf Calling ee24xx_write_page d Sd p eeaddr len buf endif rv ee24xx_write_page eeaddr len buf if DEBUG printf gt din rv endif if rv 1 return 1 eeaddr rv len rv buf rv total rv while len gt 0 return total void error void printf error TWI status x n twst exit 0 void main void uint16_t a int rv uint8_t b 16 uint8_t x ioinit fdevopen uart_putchar NULL 0 for a 0 a lt 256 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 106 printf S 04x a rv ee24xx_read_bytes a 16 b if Gey error if rv lt 16 printf warning short read d n rv a rv for x 0 x lt rv x printf 02x b x putchar An define EE_WRITE addr str ee24xx_write_bytes addr sizeof str 1 str rv EE WRITE 55 The quick brown fox jumps over the lazy do
33. Sc ns ee eb Ok GS ee ES 85 5 23 3 Compiling and Linking 0 0 0 88 5 23 4 Examining the Object File 88 253 Limker Map PUES lt x se oe we ta e ew ag a i 92 223 0 Intel Hex Files sc Lae ave SRS eee Ee es 93 323 7 Make Build th Project lt lt coos 6 ars 94 Example using the two wire interface TWI 96 5 24 1 Introduction into TWI 96 5 24 2 The TW example project lt ee o 97 5 24 3 The Senica Code so o cee oe DE we ee ao 97 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen CONTENTS iv 6 avr libc Data Structure Documentation 6 1 6 2 div Struct Reference lt lt lt a eee ee SE a o A eS 611 Detailed Descriphon oe 2 zao e es s ts es 0 1 2 Field Documentation ee socs e ee a ee idiv t Stivet Reference ocios bea eh eR RS 62 1 Detaled Description lt sees bin ee bes 62 2 Field Documentation ecos ico 7 avr libc Page Documentation TA 12 13 Acknowledgments cn o a ag AR avr libc and assembler programs 0 0 Tel ii eee 22 Anyokine the coupler 24 6 e ra 4 e i Re Tao O nod ON 7 2 4 Pseudo ops and operators o e Frequently Asked Questions e Tad PAQ TAE 2 4 2 hk eee SESE BES SHAS 7 3 2 My program doesn t recognize a variable updated within an iiterfupt routine cocoa 7 3 3 I get undefined reference to for functions like sinQ 7 3 4 How to permanently bind
34. Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 21 Special function registers 82 the compiler can optimize this into the use of an sbi instruction of course provided the target address is within the allowable range for this instruction and the right hand side of the expression is a constant value known at compile time The advantage of using the memory mapped paradigm in C programs is that it makes the programs more portable to other C compilers for the AVR platform Some people might also feel that this is more readable For example the following two statements would be equivalent outb DDRD inb DDRD amp LCDBITS DDRD amp LCDBITS The generated code is identical for both Whitout optimization the compiler strictly generates code following the memory mapped paradigm while with optimization turned on code is generated using the faster and smaller in out MCU instructions Note that special care must be taken when accessing some of the 16 bit timer IO reg isters where access from both the main program and within an interrupt context can happen See Why do some 16 bit timer registers sometimes get trashed Modules e groupAdditional notes from lt avr sfr_defs h gt Bit manipulation define _BV bit 1 lt lt bit IO register bit manipulation define bit_is_set sfr bit SFR_BYTE sfr amp _BV bit define bit_is_clear sfr bit _SFR_BYTE sfr amp _BV bit e define loop_until_bit_is_set
35. Usbic 0 SL mne rjmp 1b no outputs I _SFR_IO_ADDR port I bit 7 4 6 C Stub Functions Macro definitions will include the same assembler code whenever they are referenced This may not be acceptable for larger routines In this case you may define a C stub function containing nothing other than your assembler code void delay uint8_t ms uint16_t cnt asm volatile Xin L dli Ant mov A0 A2 n t mov B0 B2 An L_dl2 n t sbiw A0 1 n t brne L_dl2 n t dec 1 n t brne L_dli n t amp w cnt r ms r delay_count i Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 149 The purpose of this function is to delay the program execution by a specified number of milliseconds using a counting loop The global 16 bit variable delay_count must contain the CPU clock frequency in Hertz divided by 4000 and must have been set before calling this routine for the first time As described in the clobber section the routine uses a local variable to hold a temporary value Another use for a local variable is a return value The following function returns a 16 bit value read from two successive port addresses uint16_t inw uint8_t port uint16_t result asm volatile in 580 31 lat in BO 1 1 r result I _SFR_IO_ADDR port i return result Note inw is supplied by avr libc
36. _ tmp _reg__ Register r0 used for temporary storage zero_reg Register rl always zero Register rO may be freely used by your assembler code and need not be restored at the end of your code It s a good idea to use __tmp_reg__ and __zero_reg instead of rO or r1 just in case a new compiler version changes the register usage definitions 7 4 3 Input and Output Operands Each input and output operand is described by a constraint string followed by a C expression in parantheses AVR GCC 3 3 knows the following constraint characters Note The most up to date and detailed information on contraints for the avr can be found in the gcc manual The x register is r27 126 the y register is r29 r28 and the z register is r31 r30 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 142 Constraint Used for Range a Simple upper registers r16 to r23 b Base pointer registers y Z pairs d Upper register rl6tor31 e Pointer register pairs X Y Z G Floating point constant 0 0 I 6 bit positive integer 0 to 63 constant J 6 bit negative integer 63 to 0 constant K Integer constant 2 L Integer constant 0 l Lower registers r0 to r15 M 8 bit integer constant 0 to 255 N Integer constant 1 O Integer constant 8 16 24 P Integer constant 1 q Stack pointer register SPH SPL r Any register r0 to r31 t Temporary re
37. __malloc_heap_end 66 feof 46 __malloc_heap_start 66 ferror 46 __malloc_margin 67 fgetc 46 abort 58 fgets 46 abs 58 FILE 44 atof 58 fprintf 46 atoi 58 fprintf_P 47 atol 58 fputc 47 bsearch 59 fputs 47 calloc 59 fputs_P 47 div 59 fread 47 DTOSTR_ALWAYS_SIGN 57 fscanf 47 DTOSTR_PLUS_SIGN 57 fscanf_P 47 DTOSTR_UPPERCASE 57 fwrite 47 dtostre 59 getc 44 dtostrf 60 getchar 44 exit 60 gets 48 free 60 printf 48 itoa 60 printf_P 48 labs 61 putc 44 Idiv 61 putchar 44 Itoa 61 puts 48 malloc 62 puts_P 48 qsort 62 scanf 48 rand 62 scanf_P 48 RAND_MAX 57 snprintf 48 rand_r 62 snprintf_P 48 random 63 RANDOM_MAX 57 random_r 63 realloc 63 srand 63 srandom 63 strtod 63 strtol 64 strtoul 64 ultoa 65 utoa 66 avr_string Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen INDEX 184 memccpy 68 memchr 68 memcmp 68 memcpy 69 memmove 69 memset 69 strcasecmp 69 strcat 70 strchr 70 stremp 70 strcpy 70 strlcat 71 stricpy 71 strlen 71 strlwr 71 strncasecmp 72 strncat 72 strcmp 72 strncpy 72 strnlen 73 strrchr 73 strrev 73 strsep 73 strstr 74 strtok_r 74 strupr 74 avr_watchdog wdt_disable 27 wdt_enable 28 wdt_reset 28 WDTO_120MS 28 WDTO_15MS 28 WDTO_IS 28 WDTO_250MS 28 WDTO_2S 28 WDTO_30MS 29 WDTO_500MS 29 WDTO_60MS 29 avrdude usage 168 avrprog usage 1
38. a buffer overflow Conversion is done using the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 67 The ultoa function returns the pointer passed as s 5 18 4 30 char utoa unsigned int __val char x __s int __radix Convert an unsigned integer to a string The function utoa converts the unsigned integer value from val into an ASCII repre sentation that will be stored under s The caller is responsible for providing sufficient storage in s Note The minimal size of the buffer s depends on the choice of radix For example if the radix is 2 binary you need to supply a buffer with a minimal length of 8 x sizeof unsigned int 1 characters i e one character for each bit plus one for the string terminator Using a larger radix will require a smaller minimal buffer size Warning If the buffer is too small you risk a buffer overflow Conversion is done using the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a The utoa function returns the pointer passed as s 5 18 5 Variable Documentation 5 18 5 1 charx __malloc_heap_end malloc tunable 5 18 5 2 charx __malloc_heap_end amp _heap_end malloc
39. a loss of preci sion See random for an alternate set of functions that retains full 32 bit precision 5 18 4 20 int rand_r unsigned long ctx Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 64 Variant of rand that stores the context in the user supplied variable located at ct x instead of a static library variable so the function becomes re entrant 5 18 4 21 long random void The random function computes a sequence of pseudo random integers in the range of 0 to RANDOM_MAX as defined by the header file lt stdlib h gt The srandom function sets its argument seed as the seed for a new sequence of pseudo random numbers to be returned by rand These sequences are repeatable by calling srandom with the same seed value If no seed value is provided the functions are automatically seeded with a value of 1 5 18 4 22 long random_r unsigned long ctx Variant of random that stores the context in the user supplied variable located at ct x instead of a static library variable so the function becomes re entrant 5 18 4 23 void realloc void __ptr size_t __size The realloc function tries to change the size of the region allocated at pt r to the new size value It returns a pointer to the new region The returned pointer might be the same as the old pointer or a pointer to a completely different region The contents of the returned region up to either the old or t
40. a variable to a register 7 3 5 How to modify MCUCR or WDTCR early 7 3 6 What is all this _BVO stuff about Tay Canluse Cee onthe AVR ooo 7 3 8 Shouldn t I initialize all my variables 7 3 9 Why do some 16 bit timer registers sometimes get trashed 7 3 10 How do I use a define d constant in an asm statement 7 3 11 Why does the PC randomly jump around when single stepping 7 3 12 How do I trace an assembler file in avr gdb 7 3 13 How do I pass an IO port as a parameter to a function 7 3 14 What registers are used by the C compiler 110 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen CONTENTS v 7 3 15 How do I put an array of strings completely in ROM 129 7 3 16 How to use external RAM 131 Far Which Nag 10 USE o coe saoe Ba se ets Rs 132 7 3 18 How do I relocate code to a fixed address 133 7 3 19 My UART is generating nonsense My ATmegal28 keeps crashing Port F is completely broken 133 7 3 20 Why do all my foo bar strings eat up the SRAM 134 7 3 21 Why does the compiler compile an 8 bit operation that uses bitwise operators into a 16 bit operation in assembly 135 7 3 22 How to detect RAM memory and variable overlap problems 135 7 3 23 Is it really impossible to program the ATtinyXX in C 136 7 3 24 What is this clock skew detected mess
41. active master has released the bus Note 10 Next the device slave is going to be reselected using a so called repeated start con dition which is meant to guarantee that the bus arbitration will remain at the current master using the same slave address SLA but this time with read intent R W bit set to 1 in order to request the device slave to start transfering data from the slave to the master in the next packet Note 11 If the EEPROM device is still busy writing one or more cells after a previous write request it will simply leave its bus interface drivers at high impedance and does not respond to a selection in any way at all The master selecting the device will see the high level at SDA after transfering the SLA R W packet as a NACK to its selection request Thus the select process is simply started over effectively causing a repeated start condition until the device will eventually respond This polling procedure is recommended in the 24Cxx datasheet in order to minimize the busy wait time when writing Note that in case a device is broken and never responds to a selection e g since it is no longer present at all this will cause an infinite loop Thus the maximal number of iterations made until the device is declared to be not responding at all and an error is returned will be limited to MAX_ITER Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 109
42. an explicit space in the format e Matches a nonempty sequence of characters from the specified set of accepted characters the next pointer must be a pointer to char and there must be enough room for all the characters in the string plus a terminating NUL character The usual skip of leading white space is suppressed The string is to be made up of characters in or not in a particular set the set is defined by the characters between the open bracket character and a close bracket character The set excludes those characters if the first character after the open bracket is a circum flex To include a close bracket in the set make it the first character after the Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 55 open bracket or the circumflex any other position will end the set The hyphen character is also special when placed between two other characters it adds all intervening characters to the set To include a hyphen make it the last character before the final close bracket For instance 0 9 means the set of every thing except close bracket zero through nine and hyphen The string ends with the appearance of a character not in the or with a circumflex in set or when the field width runs out e p Matches a pointer value as printed by p in printf the next pointer must be a pointer to void e n Nothing is expected instead the number of characters consum
43. at location 0x60 The next available address in the bss segment is location 0x63 so the application uses 3 bytes of uninitialized data The eeprom segment where EEPROM variables are stored starts at location 0x0 The next available address in the eeprom segment is also location 0x0 so there aren t any EEPROM variables 5 23 6 Intel Hex Files We have a binary of the application but how do we get it into the processor Most if not all programmers will not accept a GNU executable as an input file so we need to do a little more processing The next step is to extract portions of the binary and save the information into hex files The GNU utility that does this is called avr objcopy The ROM contents can be pulled from our project s binary and put into the file demo hex using the following command avr objcopy j text j data O ihex demo elf demo hex The resulting demo hex file contains 100000000AC063C062C061C060C05FCO5ECO5DCO46 1000100007C05BC0O5AC011241FBECFEDCDBF4FC07B Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 94 100020001F920F920FB60F9211242F938F939F93CD 0003000809160009927009719F0019731F514C05D 0004000809161009091620001969093620080938C 0005000610080916100909162008F5F9340A9F4EC 000600081E08093600011C08091610090916200F6 10007000019790936200809361008091610090915C 100080006200892B11F410926000809161009091C0 000900062009BBD8ABD9F918F912F910F900FBEE3 000A000
44. char __c PROGMEM s amp __c 0 e define pgm_read_byte_near address_short __LPM uintl6_t address_short define pgm_read_word_near address_short t address_short define pgm_read_dword_near address_short t address_short __LPM_word uint16_ __LPM_dword uint16_ Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 7 Program Space String Utilities 20 define pgm_read_byte_far address_long _ ELPM uint32_t address_long define pgm_read_word_far address_long __ELPM_word uint32_ t address_long define pgm_read_dword_far address_long __ELPM_dword uint32_ t address_long define pgm_read_byte address_short pgm_read_byte_near address_short define pgm_read_word address_short pgm_read_word_near address_short define pgm_read_dword address_short pgm_read_dword_near address_short define PGM_P const prog_char define PGM_VOID_P const prog_void x Functions 5 7 2 void x memcpy_P void x PGM_VOID_P size_t int strcasecmp_P const char x PGM_P _ ATTR_PURE char x strcat_P char x PGM_P int stremp_P const char x PGM_P _ ATTR_PURE char strepy_P char x PGM_P size_t strlcat_P char x PGM_P size_t size_t strlcpy_P char x PGM_P size_t size_t strlen_P PGM_P __ATTR_CONST int strncasecmp_P const char x PGM_P size_t _ ATTR_PURE char x strncat_P char x PGM_P size_t int strnemp_P const char x PGM_P size_t _ ATTR_PURE char x strnc
45. characters of s1 Parameters sl A pointer to a string in the devices SRAM s2 A pointer to a string in the devices Flash n The maximum number of bytes to compare Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 7 Program Space String Utilities 25 Returns The strcasecmp_P function returns an integer less than equal to or greater than zero if sl or the first n bytes thereof is found respectively to be less than to match or be greater than s2 5 7 3 10 char x strncat_P char x dest PGM_P src size_t len Concatenate two strings The strncat_P function is similar to strncat except that the src string must be located in program space flash Returns The strncat_P function returns a pointer to the resulting string dest 5 7 3 11 int strncmp_P const char s1 PGM_P s2 size_t n The strncmp_PQ function is similar to stremp_P except it only compares the first at most n characters of s1 and s2 Returns The strncmp_P function returns an integer less than equal to or greater than zero if sl or the first n bytes thereof is found respectively to be less than to match or be greater than s2 5 7 3 12 char x strncpy_P char dest PGM_P src size_t n The strncpy_P function is similar to strepy_P except that not more than n bytes of src are copied Thus if there is no null byte among the first n bytes of src the result will not be null terminated In the case whe
46. communication is indicated by an asserted TWINT bit in Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 108 TWCR An interrupt would be generated if allowed After performing any actions that are needed for the next communication step the interrupt condition must be man ually cleared by setting the TWINT bit Unlike with many other interrupt sources this would even be required when using a true interrupt routine since as soon as TWINT is re asserted the next bus transaction will start Note 9 Since the TWI bus is multi master capable there is potential for a bus contention when one master starts to access the bus Normally the TWI bus interface unit will detect this situation and will not initiate a start condition while the bus is busy However in case two masters were starting at exactly the same time the way bus arbitration works there is always a chance that one master could lose arbitration of the bus during any transmit operation A master that has lost arbitration is required by the protocol to immediately cease talking on the bus in particular it must not initiate a stop condition in order to not corrupt the ongoing transfer from the active master In this example upon detecting a lost arbitration condition the entire transfer is going to be restarted This will cause a new start condition to be initiated which will normally be delayed until the currently
47. cope with all of these con straints and offers some tuning options that can be used if there are more resources available than in the default configuration 7 5 2 Internal vs external RAM Obviously the constraints are much harder to satisfy in the default configuration where only internal RAM is available Extreme care must be taken to avoid a stack heap collision both by making sure functions aren t nesting too deeply and don t require too much stack space for local variables as well as by being cautious with allocating too much dynamic memory If external RAM is available it is strongly recommended to move the heap into the ex ternal RAM regardless of whether or not the variables from the data and bss sections are also going to be located there The stack should always be kept in internal RAM Some devices even require this and in general internal RAM can be accessed faster since no extra wait states are required When using dynamic memory allocation and stack and heap are separated in distinct memory areas this is the safest way to avoid a stack heap collision Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 5 Using malloc 152 7 5 3 Tunables for malloc There are a number of variables that can be tuned to adapt the behavior of malloc to the expected requirements and constraints of the application Any changes to these tunables should be made before the very first call to malloc Note that s
48. decimal u or unsigned hexadecimal x and X notation The letters abcdef are used for x conversions the letters ABCDEF are used for X conversions The precision if any gives the minimum number of digits that must appear if the converted value requires fewer digits it is padded on the left with zeros Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 52 p The void argument is taken as an unsigned integer and converted similarly as a x command would do c The int argument is converted to an unsigned char and the resulting character is written s The char x argument is expected to be a pointer to an array of character type pointer to a string Characters from the array are written up to but not including a terminating NUL character if a precision is specified no more than the number specified are written If a precision is given no null character need be present if the precision is not specified or is greater than the size of the array the array must contain a terminating NUL character A is written No argument is converted The complete conversion specification is eE The double argument is rounded and converted in the format d ddde177dd where there is one digit before the decimal point char acter and the number of digits after it is equal to the precision if the precision is missing it is taken as 6 if the precision is zero no decimal point ch
49. don t specify the prefix option the tools will get installed in the usr local hierarchy i e the binaries will get installed in usr local bin the info pages get installed in usr local info etc Since these tools are chang ing frequently It is preferrable to put them in a location that is easily removed When configure is run it generates a lot of messages while it determines what is available on your operating system When it finishes it will have created several Makefiles that are custom tailored to your platform At this point you can build the project S make Note BSD users should note that the project s Makefile uses GNU make syntax This means FreeBSD users may need to build the tools by using gmake If the tools compiled cleanly you re ready to install them If you specified a destination that isn t owned by your account you ll need root access to install them To install make install You should now have the programs from binutils installed into SPREFIX bin Don t forget to set your PATH environment variable before going to build avr gcc 7 8 4 GCC for the AVR target Warning You must install avr binutils and make sure your path is set properly before in stalling avr gcc The steps to build avr gcc are essentially same as for binutils bunzip2 c gcc lt version gt tar bz2 tar xf cd gcc lt version gt mkdir obj avr cd obj avr configure prefix PREFIX target avr enable langu
50. environment variable if you wish as such using a Bourne like shell PREFIX HOME local avr export PREFIX Note Be sure that you have your PATH environment variable set to search the direc tory you install everything in before you start installing anything For example if you use prefix PREFIX you must have PREFIX bin in your exported PATH As such PATH SPATH SPREFIX bin export PATH Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 8 Installing the GNU Tool Chain 164 Warning If you have CC set to anything other than avr gcc in your environment this will cause the configure script to fail It is best to not have CC set at all Note It is usually the best to use the latest released version of each of the tools 7 8 1 Required Tools GNU Binutils http sources redhat com binutils Installation e GCC http gee giu org Installation AVR Libc http savannah gnu org projects avr libc Installation 7 8 2 Optional Tools You can develop programs for AVR devices without the following tools They may or may not be of use for you uisp http savannah gnu org projects uisp Installation e avrdude http savannah nongnu org projects avrdude Installation Usage Notes GDB http sources redhat com gdb Installation Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 8 Installing the GNU Tool Chain 165 Simulavr http
51. every thing seems correct but it isn t really The assembler code modifies the variable that ptr points to The compiler will not recognize this and may keep its value in any of the other registers Not only does the compiler work with the wrong value but the assembler code does too The C program may have modified the value too but the compiler didn t update the memory location for optimization reasons The worst thing you can do in this case is uint8_t s asm volatile in 0 _ SREG__ NANET cli Wrote ld _ tmp_reg__ al TAE inc __tmp_reg__ Tne st Sal __tmp_reg__ TAE out __SREG__ 0 MATINET amp r s e ptr memory The special clobber memory informs the compiler that the assembler code may mod ify any memory location It forces the compiler to update all variables for which the contents are currently held in a register before executing the assembler code And of course everything has to be reloaded again after this code In most situations a much better solution would be to declare the pointer destination itself volatile volatile uint8_t ptr This way the compiler expects the value pointed to by ptr to be changed and will load it whenever used and store it whenever modified Situations in which you need clobbers are very rare In most cases there will be better ways Clobbered registers will force the compiler to store their values before and reload them after your assembler code Avoiding
52. execution speed Care should be taken when such an indirect port access is going to one of the 16 bit IO registers where the order of write access is critical like some timer registers All versions of avr gcc up to 3 3 will generate instructions that use the wrong access order in this situation since with normal memory operands where the order doesn t matter this sometimes yields shorter code Seehttp mail nongnu org archive html avr libc dev 2003 01 msg00044 html for a possible workaround avr gcc versions after 3 3 have been fixed in a way where this optimization will be disabled if the respective pointer variable is declared to be volatile so the correct behaviour for 16 bit IO ports can be forced that way Back to FAQ Index 7 3 14 What registers are used by the C compiler Data types char is 8 bits int is 16 bits long is 32 bits Long long is 64 bits float and double are 32 bits this is the only supported floating point format pointers are 16 bits function pointers are word addresses to allow addressing the whole 128K program memory space on the ATmega devices with gt 64 KB of flash ROM There is a mint 8 option see Options for the C compiler avr gcc to make int 8 bits but that is not supported by avr libc and violates C standards int must be at least 16 bits It may be removed in a future release Call used registers r18 r27 r30 r31 May be allocated by gcc for local data You may use them freely
53. g using eeprom_is_ready before attempting any actual I O This library will not work with the following devices since these devices have the EEPROM IO ports at different locations AT90CAN 128 ATmega48 ATmega88 ATmega165 ATmega168 ATmegal69 ATmega325 ATmega3250 ATmega645 ATmega6450 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 4 EEPROM handling 16 avr libc declarations define eeprom_is_ready bit_is_clear EECR EEWE define eeprom_busy_wait do while eeprom_is_ready uint8_t eeprom_read_byte const uint8_t addr uint16_t eeprom_read_word const uint16_t xaddr void eeprom_read_block void buf const void addr size_t n void eeprom_write_byte uint8_t addr uint8_t val void eeprom_write_word uint16_t addr uint16_t val void eeprom_write_block const void buf void addr size_t n IAR C compatibility defines e define _EEPUT addr val eeprom_write_byte uint8_t addr uint8_ t val e define _EEGET var addr var eeprom_read_byte uint8_t addr 5 4 2 Define Documentation 5 4 2 1 define _EEGET var addr var eeprom_read_ byte uint8_t addr Read a byte from EEPROM 5 4 2 2 define _EEPUT addr val eeprom_write_byte uint8_t x addr uint8_t val Write a byte to EEPROM 5 4 2 3 define eeprom_busy_wait do while eeprom_is_ready Loops until the eeprom is no longer busy Returns Nothing 5 4 2 4 define
54. in assembler subroutines Calling C subroutines can clobber any of them the caller is re sponsible for saving and restoring Call saved registers r2 r17 r28 r29 May be allocated by gcc for local data Calling C subroutines leaves them un changed Assembler subroutines are responsible for saving and restoring these registers if changed r29 r28 Y pointer is used as a frame pointer points to local data on stack if necessary Fixed registers r0 r1 Never allocated by gcc for local data but often used for fixed purposes Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 129 rO temporary register can be clobbered by any C code except interrupt handlers which save it may be used to remember something for a while within one piece of assembler code rl assumed to be always zero in any C code may be used to remember something for a while within one piece of assembler code but must then be cleared after use clr r1 This includes any use of the f mul s u instructions which return their result in rl r0 Interrupt handlers save and clear rl on entry and restore r1 on exit in case it was non zero Function call conventions Arguments allocated left to right r25 to r8 All arguments are aligned to start in even numbered registers odd sized arguments including char have one free register above them This allows making better use of the movw instruction on
55. is a word The AVR writes data to the buffer a word at a time but addresses the buffer per byte So increment your address by 2 between calls and send 2 data bytes in a word format The LSB of the data is written to the lower address the MSB of the data is written to the higher address 5 1 2 7 define boot_page_fill_safe address data _ _boot_eeprom_spm_safe boot_page_fill address data Same as boot_page_fill except it waits for eeprom and spm operations to complete before filling the page 5 1 2 8 define boot_page_write address __boot_page_write_normal address Write the bootloader temporary page buffer to flash page that contains address Note address is a byte address in flash not a word address 5 1 2 9 define boot_page_write_safe address data __boot_eeprom_spm_safe boot_page_wrte address data Same as boot_page_write except it waits for eeprom and spm operations to complete before writing the page 5 1 2 10 define boot_rww_busy _SPMREG amp _ uint8_t _BV _ COMMON_ASB Check if the RWW section is busy 5 1 2 11 define boot_rww_enable __boot_rww_enable Enable the Read While Write memory section Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 2 CRC Computations 11 5 1 2 12 define boot_rww_enable_safe address data __boot_eeprom_spm_ safe boot_rww_enable address data Same as boot_rww_enable except waits for eeprom and spm operations to comp
56. it s normally executing compiler generated code It s important that these registers as well as the status register get saved and restored The extra code needed to do this is enabled by tagging the interrupt function with __ attribute__ interrupt These details seem to make interrupt routines a little messy but all these details are handled by the Interrupt API An interrupt routine is defined with one of two macros INTERRUPTO and SIGNAL These macros register and mark the routine as an in terrupt handler for the specified peripheral The following is an example definition of a handler for the ADC interrupt include lt avr signal h gt INTERRUPT SIG_ADC user code here Refer to the chapter explaining assembler programming for an explanation about inter rupt routines written solely in assembler language If an unexpected interrupt occurs interrupt is enabled and no handler is installed which usually indicates a bug then the default action is to reset the device by jumping to Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 20 Interrupts and Signals 77 the reset vector You can override this by supplying a function named __vector_ default which should be defined with either SIGNAL or INTERRUPTO as such include lt avr signal h gt SIGNAL __vector_default user code here The interrupt is chosen by supplying one of the symbols in following table Note that
57. ms 60 ms 120 ms 250 ms 500 ms 1 s 2 s Symbolic constants are formed by the prefix WDTO_ followed by the time Example that would select a watchdog timer expiry of approximately 500 ms wdt_enable WDTO_500MS 5 10 2 6 define WDTO_1S 6 See WDTO_15MS 5 10 2 7 define WDTO_250MS 4 See WDTO_15MS Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 11 Character Operations 30 5 10 2 8 define WDTO_2S 7 See WDTO_15MS 5 10 2 9 define WDTO_30MS 1 See WDTO_15MS 5 10 2 10 define WDTO_500MS 5 See WDTO_15MS 5 10 2 11 define WDTO_60MS 2 WDTO_15MS 5 11 Character Operations 5 11 1 Detailed Description These functions perform various operations on characters include lt ctype h gt Character classification routines These functions perform character classification They return true or false status de pending whether the character passed to the function falls into the function s classifi cation i e isdigit returns true if its argument is any value 0 though 9 inclusive int isalnum int __c __ATTR_CONST int isalpha int __c __ ATTR_CONST int isascii int __c _ ATTR_CONST int isblank int __c _ ATTR_CONST int iscntrl int __c _ ATTR_CONST int isdigit Gint_c _ ATTR_CONST int isgraph int __c _ ATTR_CONST int islower int__c _ ATTR_CONST int isprint int __c _ ATTR_CONST int ispunct int __c _ ATTR_CONST int isspace int __c _ ATTR_CONST int isupper int
58. newer devices of the ATmega series contain builtin support for interfacing the microcontroller to a two wire bus called TWI This is essentially the same called I2C by Philips but that term is avoided in Atmel s documentation due to patenting issues For the original Philips documentation see http www semiconductors philips com buses i2c index html 5 24 1 Introduction into TWI The two wire interface consists of two signal lines named SDA serial data and SCL serial clock plus a ground line of course All devices participating in the bus are connected together using open drain driver circuitry so the wires must be terminated using appropriate pullup resistors The pullups must be small enough to recharge the line capacity in short enough time compared to the desired maximal clock fre quency yet large enough so all drivers will not be overloaded There are formulas in the datasheet that help selecting the pullups Devices can either act as a master to the bus i e they initiate a transfer or as a slave they only act when being called by a master The bus is multi master capable and a particular device implementation can act as either master or slave at different times Devices are addressed using a 7 bit address coordinated by Philips transfered as the first byte after the so called start condition The LSB of that byte is R W i e it determines whether the request to the slave is to read or write data during the next
59. occur 5 14 3 18 double log10 double __x The log function returns the logarithm of argument x to base 10 If the argument is less than or equal 0 a domain error will occur 5 14 3 19 double modf double __value double __iptr The modf function breaks the argument value into integral and fractional parts each of which has the same sign as the argument It stores the integral part as a double in the object pointed to by iptr The modf function returns the signed fractional part of value 5 14 3 20 double pow double __x double _ y The function pow returns the value of x to the exponent y 5 14 3 21 double sin double __x The sin function returns the sine of x measured in radians 5 14 3 22 double sinh double __x The sinh function returns the hyperbolic sine of x 5 14 3 23 double sqrt double __x The sqrt function returns the non negative square root of x 5 14 3 24 double square double __x The function square returns x x Note This function does not belong to the C standard definition 5 14 3 25 double tan double __x The tan function returns the tangent of x measured in radians Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 15 Setjmp and Longjmp 38 5 14 3 26 double tanh double _ x The tanh function returns the hyperbolic tangent of x 5 15 Setjmp and Longjmp 5 15 1 Detailed Description While the C language has the dreaded goto statem
60. or the first n bytes thereof is found respectively to be less than to match or be greater than s2 5 19 2 17 char x strncat char x dest const char x src size_t len Concatenate two strings The strncat function is similar to strcat except that only the first n characters of src are appended to dest Returns The strncat function returns a pointer to the resulting string dest 5 19 2 18 int strncmp const char s1 const char s2 size_t len Compare two strings The strncmp function is similar to stremp except it only compares the first at most n characters of sl and s2 Returns The strncmp function returns an integer less than equal to or greater than zero if sl or the first n bytes thereof is found respectively to be less than to match or be greater than s2 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 74 5 19 2 19 char x strncpy char dest const char src size_t len Copy a string The strncpy function is similar to strcpy except that not more than n bytes of src are copied Thus if there is no null byte among the first n bytes of src the result will not be null terminated In the case where the length of src is less than that of n the remainder of dest will be padded with nulls Returns The strncpy function returns a pointer to the destination string dest 5 19 2 20 size_t strnlen const char x src size_t len Determine the length
61. rjmp 192 Oxca a 5f cO rjmp 190 Oxca c 5e co rjmp 188 Oxca e 5d c0 rjmp 186 Oxca OSO do rjmp 14 0x20 2255b 60 rjmp 182 Oxca 42 5a 60 rjmp 180 Oxca 00000016 lt __ctors_end gt 6 11 24 eor rl rl 8 1f be out 0x3f rl 63 a cf ed ldi r28 OxDF 223 ca Sd bE out 0x3d r28 61 e 4f c0 rjmp 158 Oxbe 00000020 lt __vector_8 gt volatile uint16_t pwm Note 1 volatile uint8_t direction SIGNAL SIG_OVERFLOW1 Note 2 202 If Se push rl 225 OF 92 push r0 24 Of b6 irs HO Oxst 7 63 2063 UE DE push r0 28 11 24 eor rl rl a4 25 93 push r18 Algn ZO ZEFO Z E0 2 0 ZEFO 2 EZ 2 0 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 90 ser BE 3 push r24 2e 9f 93 push r25 switch direction Note 3 30 80 91 60 00 lds r24 0x0060 34 99 27 eor r25 r25 36 00 97 sbiw r24 0x00 0 38 19 50 breg 6 0x40 3a 01 97 sbiw r24 0x01 1 36 31 5 brne 76 Ox8a 3e 14 c0 rjmp 40 0x68 case UP if pwm 1023 40 80 91 61 00 lds r24 0x0061 44 90 91 62 00 lds r25 0x0062 48 01 96 adiw r24 0x01 1 4a 90 93 62 00 sts 0x0062 r25 de 80 93 61 00 sts 0x0061 r24 52 80 91 61 00 lds r24 0x0061 56 90 91 62 00 lds r25 0x0062 5a 8f 5f subi r24 OxFF 255 5er 93 40 Spi t257 0x037 3 5e a9 f4 brne 42 Ox8a direction DOWN 60 81 e0 ldi r24 0x01 1 62 80 93 60 00 sts 0x
62. sfr bit do while bit_is_clear sfr bit e define loop_until_bit_is_clear sfr bit do while bit_is_set sfr bit 5 21 2 Define Documentation 5 21 2 1 define_BV bit 1 lt lt bit include lt avr io h gt Converts a bit number into a byte value Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 22 Demo projects 83 Note The bit shift is performed by the compiler which then inserts the result into the code Thus there is no run time overhead when using _BV 5 21 2 2 define bit_is_clear sfr bit _SFR_BYTE sfr amp _BV bit include lt avr io h gt Test whether bit bit in IO register sfr is clear This will return non zero if the bit is clear and a 0 if the bit is set 5 21 2 3 define bit_is_set sfr bit SFR_BYTE sfr amp _BV bit include lt avr io h gt Test whether bit bit in IO register sfr is set This will return a 0 if the bit is clear and non zero if the bit is set 5 21 2 4 define loop_until_bit_is_clear sfr bit do while bit_is_set sfr bit include lt avr io h gt Wait until bit bit in IO register s fr is clear 5 21 2 5 define loop_until_bit_is_set sfr bit do while bit_is_clear sfr bit include lt avr io h gt Wait until bit bit in IO register s fr is set 5 22 Demo projects 5 22 1 Detailed Description Various small demo projects are provided to illustrate several aspects of using the open source utilities for the
63. snprintf char __s size_t __n const char x__fmt int snprintf_P char __s size_t __n const char x__fmt int vsprintf char __s const char __fmt va_list ap int vsprintf_P char __s const char __fmt va_list ap int vsnprintf char __s size_t __n const char __fmt va_list ap int vsnprintf_P char __s size_t __n const char __fmt va_list ap int fprintf FILE __stream const char __fmt int fprintf_P FILE x__stream const char __fmt int fputs const char x__str FILE x__stream int fputs_P const char __str FILE __stream int puts const char __str int puts_P const char __str size_t fwrite const void __ptr size_t __size size_t __nmemb FILE _ stream int fgetc FILE __stream int ungetc int __c FILE __stream char fgets char x__str int __size FILE x __ stream char gets char x__str size_t fread void __ ptr size_t__ size size_t__nmemb FILE __ stream void clearerr FILE __stream int feof FILE __stream Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 45 int ferror FILE __stream int vfscanf FILE __stream const char x__fmt va_list __ap int vfscanf_P FILE __stream const char x__fmt va_list __ap int fscanf FILE __stream const char __fmt int fscanf_P FILE x_ stream const char x__fmt int scanf const char __fmt int scanf_P const char x__fmt int
64. than 8 KB of ROM avr4 Enhanced CPU core up to 8 KB of ROM avr5 Enhanced CPU core more than 8 KB of ROM By default code is generated for the avr2 architecture Note that when only using mmcu architecture but no mmcu MCU type including the file lt avr io h gt cannot work since it cannot decide which device s definitions to select e mmcu MCU type The following MCU types are currently understood by avr gcc The table matches them against the corresponding avr gcc architecture name and shows the preprocessor symbol declared by the mmcu option Architecture MCU name Macro avrl at90s1200 __AVR_AT90S1200__ avr 1 attiny 11 __AVR_ATtiny11__ avrl attiny12 __AVR_ATtiny12__ avrl attiny 15 __AVR_ATtiny15__ avrl attiny28 __AVR_ATtiny28__ avr2 at90s2313 __AVR_AT90S2313__ avr2 at90s2323 __AVR_AT90S2323__ avr2 at90s2333 __AVR_AT90S2333__ avr2 at90s2343 __ AVR_AT90S2343__ avr2 attiny22 __AVR_ATtiny22__ avr2 attiny26 __AVR_ATtiny26__ avr2 at90s4414 _ AVR_AT90S4414__ avr2 at90s4433 __ AVR_AT90S4433__ avr2 at90s4434 __ AVR_AT90S4434__ avr2 at90s8515 __AVR_AT90S8515__ avr2 at90c8534 _ AVR_AT90C8534__ avr2 at90s8535 __ AVR_AT90S8535__ avr2 at86rf401 __AVR_AT86RF401__ avr2 attiny 13 __AVR_ATtiny13__ avr2 attiny2313 __AVR_ATtiny2313__ avr3 atmega 103 __AVR_ATmegal03__ avr3 atmega603 __AVR_ATmega603__ Generated on Tue Feb 15 16 09 56
65. that opens a stream for writing will cause the resulting stream to be aliased to both stdout and stderr Thus if the open was done with both read and write intent all three standard streams will be identical Note that these aliases are indistinguishable from each other thus calling fclose on such a stream will also effectively close all of its aliases note 3 All the printf and scanf family functions come in two flavours the standard name where the format string is expected to be in SRAM as well as a version with the suffix _P where the format string is expected to reside in the flash ROM The macro PSTR explained in Program Space String Utilities becomes very handy for declaring these format strings Note 1 It might have been possible to implement a device abstraction that is compatible with fopen but since this would have required to parse a string and to take all the information needed either out of this string or out of an additional table that would need to be provided by the application this approach was not taken Note 2 This basically follows the Unix approach if a device such as a terminal needs special handling it is in the domain of the terminal device driver to provide this functionality Thus a simple function suitable as put for fdevopen that talks to a UART interface might look like this int uart_putchar char c if c An uart_putchar r loop_until_bit_is_set UCSRA UD
66. the enhanced core If too many those that don t fit are passed on the stack Return values 8 bit in r24 not r25 16 bit in r25 r24 up to 32 bits in r22 r25 up to 64 bits in r18 r25 8 bit return values are zero sign extended to 16 bits by the caller unsigned char is more efficient than signed char just clr r25 Argu ments to functions with variable argument lists printf etc are all passed on stack and char is extended to int Warning There was no such alignment before 2000 07 01 including the old patches for gcc 2 95 2 Check your old assembler subroutines and adjust them accordingly Back to FAQ Index 7 3 15 How do I put an array of strings completely in ROM There are times when you may need an array of strings which will never be modified In this case you don t want to waste ram storing the constant strings The most obvious and incorrect thing to do is this include lt avr pgmspace h gt PGM_P array 2 PROGMEM ROO Bar int main void char buf 32 strcpy_P buf array 1 return 0 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 130 The result is not want you want though What you end up with is the array stored in ROM while the individual strings end up in RAM in the data section To work around this you need to do something like this include lt avr pgmspace h gt const char foo PROGMEM Foo cons
67. to checkout multiple source trees in a single directory without having them clobber each other If you don t know how to do this you probably shouldn t be making releases or cutting branches Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 6 Release Numbering and Methodology 156 7 6 2 1 Creating a cvs branch The following steps should be taken to cut a branch in cvs 1 Check out a fresh source tree from cvs HEAD 2 Update the NEWS file with pending release number and commit to cvs HEAD Change Changes since avr libc lt last_release gt to Changes in avr libc lt this_relelase gt 3 Set the branch point tag setting lt major gt and lt minor gt accordingly cvs tag avr libc lt major gt _ lt minor gt branchpoint 4 Create the branch cvs tag b avr lib lt major gt _ lt minor gt branch 5 Update the package version in configure in and commit configure in to cvs HEAD Change minor number to next odd value 6 Update the NEWS file and commit to cvs HEAD Add Changes since avr libc lt this_release gt 7 Check out a new tree for the branch CVS CO r avr lib lt major gt _ lt minor gt branch 8 Update the package version in configure in and commit configure in to cvs branch Change the patch number to 90 to denote that this now a branch leading up to a release Be sure to leave the lt date gt part of the version 9 Bring the build system up to date b
68. void set_bits_func_wrong PORTB Oxaa set_bits_func_correct amp PORTB 0x55 set_bits_macro PORTB Oxf0 return 0 The first function will generate object code which is not even close to what is intended The major problem arises when the function is called When the compiler sees this call it will actually pass the value of the PORTB register using an IN instruction instead of passing the address of PORTB e g memory mapped io addr of 0x38 io port 0x18 for the mega128 This is seen clearly when looking at the disassembly of the call Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 127 set_bits_func_wrong PORTB Oxaa 10a 6a ea ldi r22 OxAA 7 TO 106 88 b3 in r24 0x18 24 10e Oe 94 65 00 call Oxca So the function once called only sees the value of the port register and knows nothing about which port it came from At this point whatever object code is generated for the function by the compiler is irrelevant The interested reader can examine the full disassembly to see that the function s body is completely fubar The second function shows how to pass by reference the memory mapped address of the io port to the function so that you can read and write to it in the function Here s the object code generated for the function call set_bits_func_correct amp PORTB 0x55 112 65 e5 1di r22 0x55 85 114 88 e3 ldi r24 0x38 556 116 90 e0 1di
69. with wide or multi byte characters Returns The strchr function returns a pointer to the matched character or NULL if the character is not found 5 19 2 10 int stremp const char x s1 const char s2 Compare two strings The stremp function compares the two strings sl and s2 Returns The stremp function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 72 5 19 2 11 char x strcpy char x dest const char src Copy a string The strcpy function copies the string pointed to by src including the terminating 0 character to the array pointed to by dest The strings may not overlap and the destination string dest must be large enough to receive the copy Returns The strcpy function returns a pointer to the destination string dest Note If the destination string of a strcpy is not large enough that is if the programmer was stupid lazy and failed to check the size before copying then anything might happen Overflowing fixed length strings is a favourite cracker technique 5 19 2 12 size_t strlcat char x dst const char x src size_t siz Concatenate two strings Appends src to string dst of size siz unlike strncat siz is the full size of dst not space left At most siz 1 characters will be copied Always NULL terminates un
70. 0060 r24 66 11 c0 rjmp 34 Ox8a break case DOWN if pwm 0 68 80 91 61 00 lds r24 0x0061 6c 90 91 62 00 lds r25 0x0062 TOs 01197 sbiw r24 0x01 1 72 90 93 62 00 sts 0x0062 r25 76 80 93 61 00 sts 0x0061 r24 7a 80 91 61 00 lds r24 0x0061 7e 90 91 62 00 lds r25 0x0062 82 89 2b or r24 r25 84 11 4 brne 4 Ox8a direction UP 86 10 92 60 00 sts 0x0060 rl break OCR pwm Note 4 8a 80 91 61 00 lds r24 0x0061 8e 90 91 62 00 lds r25 0x0062 92 9b bd out Ox2b r25 43 94 8a bd out 0x2a r24 42 96 gt SF 91 pop r25 98 8 91 pop r24 Jat 24 81 pop r18 9c Of 90 pop EO 9e Of be out Ox3 r 063 a0 Of 90 pop ro az 16 94 pop rl Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 91 a4 18 95 reti 000000a6 lt ioinit gt void ioinit void Note 5 tmrl is 10 bit PWM TCCRIA _BV PWM10 _BV PWM11 _BV XCOM11 a6 83 e8 ldi r24 0x83 131 a8 8f bd out 0x2f r24 47 tmrl running on full MCU clock TCCRIB _BV CS10 aa 81 e0 ldi r24 0x01 1 ac 8e bd out 0x2e r24 46 set PWM value to 0 OCR 0 ae 1b bc out 0x2b rl 43 b0 la bc out 0x2a rl 42 enable OC1 and PB2 as output DDROC _BV OC1 b2 82 e0 ldi r24 0x02 2 b4 87 bb out Ox17 24 23 timer_enable_int _BV TOIE1 enable interrupts sei int main void ioinit
71. 0F901F90189583E88FBD81E08EBD1BBCIB 000B0001ABC82E087BB84E089BF78940895CFEDB5 0C00COOODOEODEBFCDBFEFDFFFCF9ACF56 00000001FF The j option indicates that we want the information from the text and data segment extracted If we specify the EEPROM segment we can generate a hex file that can be used to program the EEPROM avr objcopy j eeprom change section Ima eeprom 0 O ihex demo elf demo_eeprom hex The resulting demo_eeprom hex file contains 00000001FF which is an empty hex file which is expected since we didn t define any EEPROM variables 5 23 7 Make Build the Project Rather than type these commands over and over they can all be placed in a make file To build the demo project using make save the following in a file called Makefile Note This Makefile can only be used as input for the GNU version of make PRG demo OBJ demo o MCU_TARGET atmega8 OPTIMIZE 02 DEF S LIBS You should not have to change anything below here CE avr gcc Override is only needed by avr lib build system override CFLAGS g Wall OPTIMIZE mmcu MCU_TARGET DEFS Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 95 override LDFLAGS W1 Map PRG map OBJCOPY avr objcopy OBJDUMP avr objdump all PRG elf lst text eeprom S PRG elf OBJ CC CFLAGS S LDFLAGS o LIBS clean fm rf o S PRG elf eps png pd
72. 15 Idiv_t Idiv long __num long __denom The Idiv function computes the value num denom and returns the quotient and re mainder in a structure named 1div_t that contains two long integer members named quot and rem 5 18 4 16 char Itoa long int __val char x __s int _ radix Convert a long integer to a string The function Itoa converts the long integer value from val into an ASCII represen tation that will be stored under s The caller is responsible for providing sufficient storage in s Note The minimal size of the buffer s depends on the choice of radix For example if the radix is 2 binary you need to supply a buffer with a minimal length of 8 sizeof long int 1 characters i e one character for each bit plus one for the string terminator Using a larger radix will require a smaller minimal buffer size Warning If the buffer is too small you risk a buffer overflow Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 63 Conversion is done using the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a If radix is 10 and val is negative a minus sign will be prepended The ltoa function returns the pointer passed as s 5 18 4 17 void malloc size_t __ size The malloc function allocates size bytes of memory If malloc fails a NULL pointer is returned
73. 22 r21 120 r19 r18 r30 r31 r26 r27 r28 r29 r17 r16 r15 r14 r13 r12 r11 r10 r9 r8 r7 r6 r5 r4 r3 r2 r1 rO e mint8 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 174 Assume int to be an 8 bit integer Note that this is not really supported by avr libc so it should normally not be used The default is to use 16 bit integers e mno interrupts Generates code that changes the stack pointer without disabling interrupts Normally the state of the status register SREG is saved in a temporary register interrupts are disabled while changing the stack pointer and SREG is restored e mcall prologues Use subroutines for function prologue epilogue For complex functions that use many registers that needs to be saved restored on function entry exit this saves some space at the cost of a slightly increased execution time e minit stack nnnn Set the initial stack pointer to nnnn By default the stack pointer is initialized to the symbol __stack which is set to RAMEND by the run time initialization code e mtiny stack Change only the low 8 bits of the stack pointer e mno tablejump Do not generate tablejump instructions By default jump tables can be used to op timize switch statements When turned off sequences of compare statements are used instead Jump tables are usually faster to execute on average but in particular for switch state
74. 68 bit_is_clear avr_sfr 82 bit_is_set avr_sfr 82 boot_is_spm_interrupt avr_boot 7 boot_lock_bits_set avr_boot 8 boot_lock_bits_set_safe avr_boot 8 boot_page_erase avr_boot 8 boot_page_erase_safe avr_boot 8 boot_page_fill avr_boot 8 boot_page_fill_safe avr_boot 9 boot_page_write avr_boot 9 boot_page_write_safe avr_boot 9 boot_rww_busy avr_boot 9 boot_rww_enable avr_boot 9 boot_rww_enable_safe avr_boot 9 boot_spm_busy avr_boot 10 boot_spm_busy_wait avr_boot 10 boot_spm_interrupt_disable avr_boot 10 boot_spm_interrupt_enable avr_boot 10 Bootloader Support Utilities 6 BOOTLOADER_SECTION avr_boot 10 bsearch avr_stdlib 59 Busy wait delay loops 12 calloc avr_stdlib 59 ceil avr_math 34 Character Operations 29 clearerr avr_stdio 45 cli Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen INDEX 185 avr_interrupts 78 cos avr_math 34 cosh avr_math 34 CRC Computations 10 ctype isalnum 30 isalpha 30 isascii 30 isblank 30 iscntrl 30 isdigit 30 isgraph 30 islower 30 isprint 30 ispunct 31 isspace 31 isupper 31 isxdigit 31 toascii 31 tolower 31 toupper 31 Demo projects 82 disassembling 87 div avr_stdlib 59 div_t 109 quot 109 rem 109 DTOSTR_ALWAYS_SIGN avr_stdlib 57 DTOSTR_PLUS_SIGN avr_stdlib 57 DTOSTR_UPPERCASE avr_stdlib 57 dtostre avr_stdlib 59 dtostrf avr_stdlib 60 EDOM avr_errno 32
75. 7 an output TCCR2 _BV COM20 _BV CTC2 _BV CS20 DDRD _BV PD7 Back to FAQ Index 7 3 7 Can I use C on the AVR Basically yes C is supported assuming your compiler has been configured and compiled to support it of course Source files ending in cc cpp or C will automati cally cause the compiler frontend to invoke the C compiler Alternatively the C compiler could be explicitly called by the name avr c However there s currently no support for libstdc the standard support library needed for a complete C implementation This imposes a number of restrictions on the C programs that can be compiled Among them are e Obviously none of the C related standard functions classes and template classes are available The operators new and delete are not implemented attempting to use them will cause the linker to complain about undefined external references This could perhaps be fixed Some of the supplied include files are not C safe i e they need to be wrapped into extern TO This could certainly be fixed too Exceptions are not supported Since exceptions are enabled by default in the C frontend they explicitly need to be turned off using fno exceptions in the compiler options Failing this the linker will complain about an undefined external reference to__ gx x_personality_sj0 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Qu
76. AGS I lt hdr_path gt LDFLAGS L lt lib_path gt configure prefix PREFIX 7 9 Using the avrdude program Note This section was contributed by Brian Dean bsdtbsdhome com The avrdude program was previously called avrprog The name was changed to avoid confusion with the avrprog program that Atmel ships with AvrStudio avrdude is a program that is used to update or read the flash and EEPROM memories of Atmel AVR microcontrollers on FreeBSD Unix It supports the Atmel serial pro gramming protocol using the PC s parallel port and can upload either a raw binary file Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 9 Using the avrdude program 170 or an Intel Hex format file It can also be used in an interactive mode to individually update EEPROM cells fuse bits and or lock bits if their access is supported by the Atmel serial programming protocol The main flash instruction memory of the AVR can also be programmed in interactive mode however this is not very useful because one can only turn bits off The only way to turn flash bits on is to erase the entire memory using avrdude s e option avrdude is part of the FreeBSD ports system To install it simply do the following cd usr ports devel avrdude make install Once installed avrdude can program processors using the contents of the hex file specified on the command line In this example the file main hex is burned into the flash memory
77. Back to FAQ Index 7 3 6 What is all this__BV stuff about When performing low level output work which is a very central point in microcon troller programming it is quite common that a particular bit needs to be set or cleared in some IO register While the device documentation provides mnemonic names for the various bits in the IO registers and the AVR device specific IO definitions reflect these names in definitions for numerical constants a way is needed to convert a bit number usually within a byte register into a byte value that can be assigned directly to the register However sometimes the direct bit numbers are needed as well e g in an sbi call so the definitions cannot usefully be made as byte values in the first place So in order to access a particular bit number as a byte value use the _BV macro Of course the implementation of this macro is just the usual bit shift which is done Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 121 by the compiler anyway thus doesn t impose any run time penalty so the following applies _BV 3 gt 1 lt lt 3 gt 0x08 However using the macro often makes the program better readable BV stands for bit value in case someone might ask you Example clock timer 2 with full IO clock CS2x 0b001 toggle OC2 output on compare match COM2x 0b01 and clear timer on compare match CTC2 1 Make OC2 PD
78. D 103 EEPROMs are only capable of writing one page simultaneously so care must be taken to not cross a page boundary within one write cycle The amount of data one page consists of varies from manufacturer to manufacturer some vendors only use 8 byte pages for the smaller devices and 16 byte pages for the larger devices while other vendors generally use 16 byte pages We thus use the smallest common denominator of 8 bytes per page declared by the macro PAGE_SIZE above The function simply returns after writing one page returning the actual number of data byte written It is up to the caller to re invoke it in order to write further data A FF F F F F F F F int ee24xx_write_page uint16_t eeaddr int len uint8_t buf uint8_t sla n 0 int rv 0 uint16_t endaddr if eeaddr len lt eeaddr PAGE_SIZE 1 endaddr eeaddr len else endaddr eeaddr PAGE_SIZE 1 1 len endaddr eeaddr patch high bits of EEPROM address into SLA sla TWI_SLA_24CXX eeaddr gt gt 8 amp 0x07 lt lt 1 restart if n gt MAX_ITER return 1 begin Note 15 TWCR _BV TWINT _BV TWSTA _BV TWEN send start condition while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_REP_START OK but should not happen case TW_START break case TW_MT_ARB_LOST goto begin default retu
79. EEPROM handling 14 eeprom_busy_wait avr_eeprom 15 eeprom_is_ready avr_eeprom 15 eeprom_read_block avr_eeprom 16 eeprom_read_byte avr_eeprom 16 eeprom_read_word avr_eeprom 16 eeprom_write_block avr_eeprom 16 eeprom_write_byte avr_eeprom 16 eeprom_write_word avr_eeprom 16 EMPTY _INTERRUPT avr_interrupts 78 enable_external_int avr_interrupts 79 EOF avr_stdio 44 ERANGE avr_errno 32 Example using the two wire interface TWI 95 exit avr_stdlib 60 exp avr_math 34 fabs avr_math 34 FAQ 117 fclose avr_stdio 45 fdevopen avr_stdio 45 feof avr_stdio 46 ferror avr_stdio 46 fgetc avr_stdio 46 fgets avr_stdio 46 FILE Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen INDEX 186 avr_stdio 44 floor avr_math 35 fmod avr_math 35 fprintf avr_stdio 46 fprintf_P avr_stdio 47 fputc avr_stdio 47 fputs avr_stdio 47 fputs_P avr_stdio 47 fread avr_stdio 47 free avr_stdlib 60 frexp avr_math 35 fscanf avr_stdio 47 fscanf_P avr_stdio 47 fwrite avr_stdio 47 General utilities 55 getc avr_stdio 44 getchar avr_stdio 44 gets avr_stdio 48 installation 162 installation avarice 168 installation avr libc 166 installation avrdude 167 installation avrprog 167 installation binutils 164 installation gcc 165 Installation gdb 167 installation simulavr 167 installation uisp 166 intl6_t avr_stdint 40
80. Index 7 3 21 Why does the compiler compile an 8 bit operation that uses bitwise oper ators into a 16 bit operation in assembly Bitwise operations in Standard C will automatically promote their operands to an int which is by default 16 bits in avr gcc To work around this use typecasts on the operands including literals to declare that the values are to be 8 bit operands This may be especially important when clearing a bit var amp mask wrong way The bitwise not operator will also promote the value in mask to an int To keep it an 8 bit value typecast before the not operator var amp unsigned char mask Back to FAQ Index 7 3 22 How to detect RAM memory and variable overlap problems You can simply run avr nm on your output ELF file Run it with the n option and it will sort the symbols numerically by default they are sorted alphabetically Look for the symbol _end that s the first address in RAM that is not allocated by a variable avr gcc internally adds 0x800000 to all data bss variable addresses so please ignore this offset Then the run time initialization code initializes the stack pointer by default to point to the last avaialable address in internal SRAM Thus the region between _ end and the end of SRAM is what is available for stack If your application uses malloc which e g also can happen inside printf the heap for dynamic memory is also located there See Us
81. Interrupt4 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 20 Interrupts and Signals Signal Name Description SIG_INTERRUPTS External Interrupt5 SIG_INTERRUPT6 External Interrupt6 SIG_INTERRUPT7 External Interrupt7 SIG_OUTPUT_COMPAREO Output Compare0 Interrupt SIG_OUTPUT_COMPAREIA Output Compare1 A Interrupt SIG_OUTPUT_COMPAREIB Output Compare1 B Interrupt SIG_OUTPUT_COMPAREIC Output Compare1 C Interrupt SIG_OUTPUT_COMPARE2 Output Compare2 Interrupt SIG_OUTPUT_COMPARE3A Output Compare3 A Interrupt SIG_OUTPUT_COMPARE3B Output Compare3 B Interrupt SIG_OUTPUT_COMPARE3C Output Compare3 C Interrupt SIG_OVERFLOWO Overflow0 Interrupt SIG_OVERFLOW1 Overflow 1 Interrupt SIG_OVERFLOW2 Overflow2 Interrupt SIG_OVERFLOW3 Overflow3 Interrupt SIG_PIN SIG_PIN_CHANGEO SIG_PIN_CHANGE1 SIG_RDMAC SIG_SPI SPI Interrupt SIG_SPM_READY Store program memory ready SIG_SUSPEND_RESUME SIG_TDMAC SIG_UARTO SIG_UARTO_DATA SIG_UARTO_RECV SIG_UARTO_TRANS SIG_UARTI SIG_UART1_DATA SIG_UART1_RECV SIG_UARTI_TRANS SIG_UART_DATA SIG_UART_RECV SIG_UART_TRANS SIG_USARTO_DATA SIG_USARTO_RECV SIG_USARTO_TRANS SIG_USART1_DATA SIG_USART1_RECV SIG_USART1_TRANS SIG_USB_HW ART 0 Data Register Empty Interrupt ART 0 Receive Complete Interrupt ART 0 Transmit Complete Interrupt ajaja ART 1 Data Register Empty Inter
82. RE UDR c return 0 Note 3 This implementation has been chosen because the cost of maintaining an alias is considerably smaller than the cost of maintaining full copies of each stream Yet providing an implementation that offers the complete set of standard streams was deemed to be useful Not only that writing printf instead of fprintf mystream saves typing work but since avr gcc needs to re sort to pass all arguments of variadic functions on the stack as opposed to passing them in registers for functions that take a fixed number of parameters the ability to pass one parameter less by implying st din will also save some execution time Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 44 Defines define FILE struct __file define stdin __iob 0 define stdout __iob 1 define stderr __iob 2 define EOF 1 define putc __c __ stream fputc __c __ stream define putchar __c fputc __c stdout define getc __stream fgetc __stream define getchar fgetc stdin Functions int fclose FILE __ stream int vfprintf FILE __stream const char x__fmt va_list __ap int vfprintf_P FILE __stream const char x__fmt va_list __ap int fputc int __c FILE __stream int printf const char __fmt int printf_P const char __fmt int sprintf char __s const char x__fmt int sprintf P char __s const char __fmt int
83. Sometimes it is convenient to think of the initN and finiN sections as functions but in reality they are just symbolic names which tell the linker where to stick a chunk of code which is not a function Notice that the examples for asm and C can not be called as functions and should not be jumped into The initN sections are executed in order from 0 to 9 init0 Weakly bound to __init If user defines __init it will be jumped into immedi ately after a reset initi Unused User definable Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 7 Memory Sections 161 init2 In C programs weakly bound to initialize the stack init3 Unused User definable init4 Copies the data section from flash to SRAM Also sets up and zeros out the bss sec tion In Unix like targets data is normally initialized by the OS directly from the executable file Since this is impossible in an MCU environment avr gcc instead takes care of appending the data variables after text in the flash ROM image init4 then defines the code weakly bound which takes care of copying the contents of data from the flash to SRAM init5 Unused User definable init6 Unused for C programs but used for constructors in C programs init7 Unused User definable init8 Unused User definable init9 Jumps into main 7 7 7 The finiN Sections These sections are used to define the exit code executed af
84. TROL_REG r uint8_t _BV _WD_CHANGE_BIT BV WDE MEE N Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 10 Watchdog timer handling 29 Disable the watchdog timer if possible This attempts to turn off the Enable bit in the watchdog control register See the datasheet for details 5 10 2 2 define wdt_enable timeout _wdt_write timeout Enable the watchdog timer configuring it for expiry after t imeout which is a com bination of the WDPO through WDP2 bits to write into the WDTCR register For those devices that have a WDTCSR register it uses the combination of the WDPO through WDP 3 bits See also the symbolic constants WDTO_15MS et al 5 10 2 3 define wdt_reset __asm volatile__ wdr Reset the watchdog timer When the watchdog timer is enabled a call to this instruction is required before the timer expires otherwise a watchdog initiated device reset will occur 5 10 2 4 define WDTO_120MS 3 See WDTO_15MS 5 10 2 5 define WDTO_15MS 0 Symbolic constants for the watchdog timeout Since the watchdog timer is based on a free running RC oscillator the times are approximate only and apply to a supply voltage of 5 V At lower supply voltages the times will increase For older devices the times will be as large as three times when operating at Vcc 3 V while the newer devices e g ATmegal28 ATmega8 only experience a negligible change Possible timeout values are 15 ms 30
85. _ val char __ width char __prec char x__s Defines define RAND_MAX 0x7FFF Typedefs typedef int __compar_fn_t const void const void x Functions __inline__ void abort void _ ATTR_NORETURN_ int abs int _1 __ATTR_CONST long labs long __i _ ATTR_CONST void bsearch const void __key const void __base size_t __nmemb size_t size int __compar const void const void div_t div int _ num int _ denom __asm__ __divmodhi4 _ ATTR_ CONST__ Idiv_t Idiv long __num long __denom __asm__ __divmodsi4 __ATTR_ CONST__ void qsort void x __base size_t __nmemb size_t __size __compar_fn_t _ compar long strtol const char __nptr char __endptr int __ base unsigned long strtoul const char __nptr char __endptr int __ base Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 58 e __inline__ long atol const char __nptr _ ATTR_PURE e __inline__ int atoi const char __nptr _ ATTR_PURE void exit int __ status _ ATTR_NORETURN_ void x malloc size_t__size __ATTR_MALLOC__ void free void x__ ptr void x calloc size_t __nele size_t__size __ATTR_MALLOC__ void x realloc void __ ptr size_t__size __ATTR_MALLOC__ double strtod const char __nptr char x x__endptr double atof const char __nptr int rand void void srand unsigned int __seed int rand_r unsigned long ctx Variables size_t__malloc_ma
86. __c _ ATTR_CONST int isxdigit int__c _ ATTR_CONST Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 11 Character Operations 31 Character convertion routines If c is not an unsigned char value or EOF the behaviour of these functions is undefined e int toascii int __c _ ATTR_CONST int tolower int__c _ ATTR_CONST e int toupper int __c __ATTR_CONST 5 11 2 Function Documentation 5 11 2 1 intisalnum int ___c Checks for an alphanumeric character It is equivalent to isalpha c isdigit c 5 11 2 2 int isalpha int __c Checks for an alphabetic character It is equivalent to isupper c islower c 5 11 2 3 int isascii int __c Checks whether c is a 7 bit unsigned char value that fits into the ASCII character set 5 11 2 4 int isblank int __c Checks for a blank character that is a space or a tab 5 11 2 5 intiscntrl int ___c Checks for a control character 5 11 2 6 int isdigit int __c Checks for a digit 0 through 9 5 11 2 7 int isgraph int __c Checks for any printable character except space 5 11 2 8 int islower int __c Checks for a lower case character Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 12 System Errors errno 32 5 11 2 9 int isprint int __c Checks for any printable character including space 5 11 2 10 int ispunct int __c Checks for any print
87. __iob 2 Stream destined for error output Unless specifically assigned identical to stdout If stderr should point to another stream the result of another fdevopen must be explicitly assigned to it without closing the previous st derr since this would also close stdout 5 17 2 8 define stdin __iob 0 Stream that will be used as an input stream by the simplified functions that don t take a stream argument The first stream opened with read intent using fdevopen will be assigned to stdin 5 17 2 9 define stdout __iob 1 Stream that will be used as an output stream by the simplified functions that don t take a stream argument The first stream opened with write intent using fdevopen will be assigned to both stdin and stderr 5 17 3 Function Documentation 5 17 3 1 void clearerr FILE x __ stream Clear the error and end of file flags of st ream 5 17 3 2 int fclose FILE x __ stream This function closes st ream and disallows and further IO to and from it It currently always returns 0 for success 5 17 3 3 FILE fdevopen int put char int x get void int opts __attribute_ _ unused This function is a replacement for fopen It opens a stream for a device where the actual device implementation needs to be provided by the application If successful a pointer to the structure for the opened stream is returned Reasons for a possible failure currently include that neither the put n
88. _interrupt_disable _SPM_REG amp uint8_t _ BV SPMIE define boot_is_spm_interrupt _SPM_REG amp uint8_t _BV SPMIE define boot_rww_busy _SPM_REG amp uint8_t _ BV _COMMON_ASB define boot_spm_busy _SPM_REG amp uint8_t _BV SPMEN define boot_spm_busy_wait do while boot_spm_busy define boot_page_fill address data __boot_page_fill_normal address data define boot_page_erase address __ boot_page_erase_normal address define boot_page_write address __ boot_page_write_normal address define boot_rww_enable __boot_rww_enable define boot_lock_bits_set lock_bits __ boot_lock_bits_set lock_bits define boot_page_fill_safe address data __boot_eeprom_spm_safe boot_ page_fill address data define boot_page_erase_safe address data __ boot_eeprom_spm_safe boot_ page_erase address data define boot_page_write_safe address data __ boot_eeprom_spm_safe boot_ page_wrte address data define boot_rww_enable_safe address data boot_eeprom_spm_safe boot_rww_enable address data define boot_lock_bits_set_safe address data boot_eeprom_spm_safe boot_lock_bits_set address data Define Documentation 5 1 2 1 define boot_is_spm_interrupt _SPM_REG amp uint8_t _ BV SPMIE Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 1 Bootloader Support Utilities 9 Check if the SPM interrupt is enabled 5 1 2 2 define boot
89. _lock_bits_set lock_bits __boot_lock_bits_set lock_bits Set the bootloader lock bits Parameters lock_bits A mask of which Boot Loader Lock Bits to set Note In this context a set bit will be written to a zero value For example to disallow the SPM instruction from writing to the Boot Loader memory section of flash you would use this macro as such boot_lock_bits_set _BV BLB12 And to remove any SPM restrictions you would do this boot_lock_bits_set 0 5 1 2 3 define boot_lock_bits_set_safe address data __boot_eeprom_spm_ safe boot_lock_bits_set address data Same as boot_lock_bits_set except waits for eeprom and spm operations to complete before setting the lock bits 5 1 2 4 define boot_page_erase address __boot_page_erase_normal address Erase the flash page that contains address Note address is a byte address in flash not a word address 5 1 2 5 define boot_page_erase_safe address data __boot_eeprom_spm_safe boot_page_erase address data Same as boot_page_erase except it waits for eeprom and spm operations to complete before erasing the page Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 1 Bootloader Support Utilities 10 5 1 2 6 define boot_page_fill address data __boot_page fill normal address data Fill the bootloader temporary page buffer for flash address with data word Note The address is a byte address The data
90. a needs to be explicitly requested using 1m See also the entry in the FAQ explaining this Conventionally Makefiles use the make macro LDLIBS to keep track of 1 and possibly L options that should only be appended to the C compiler command line Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 11 Todo List 180 when linking the final binary In contrast the macro LDF LAGS is used to store other command line options to the C compiler that should be passed as options during the linking stage The difference is that options are placed early on the command line while libraries are put at the end since they are to be used to resolve global symbols that are still unresolved at this point Specific linker flags can be passed from the C compiler command line using the W1 compiler option see above This option requires that there be no spaces in the appended linker option while some of the linker options above like Map or def sym would require a space In these situations the space can be replaced by an equal sign as well For example the following command line can be used to compile foo c into an executable and also produce a link map that contains a cross reference list in the file foo map avr gcc O o foo out Wl Map fo0 map Wl cref foo c Alternatively a comma as a placeholder will be replaced by a space before passing the option to the linker So for a device with external SRAM the following co
91. able character which is not a space or an alphanumeric character 5 11 2 11 int isspace int __c Checks for white space characters For the avr libc library these are space form feed f newline n carriage return r horizontal tab 1 and vertical tab Av 5 11 2 12 int isupper int _ c Checks for an uppercase letter 5 11 2 13 int isxdigit int __c Checks for a hexadecimal digits ie oneof0123456789abcdefABCDERE 5 11 2 14 int toascii int __c Converts c to a 7 bit unsigned char value that fits into the ASCII character set by clearing the high order bits Warning Many people will be unhappy if you use this function This function will convert accented letters into random characters 5 11 2 15 int tolower int __c Converts the letter c to lower case if possible 5 11 2 16 int toupper int _ c Converts the letter c to upper case if possible 5 12 System Errors errno 5 12 1 Detailed Description include lt errno h gt Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 13 Integer Type conversions 33 Some functions in the library set the global variable errno when an error occurs The file lt errno h gt provides symbolic names for various error codes Warning The errno global variable is not safe to use in a threaded or multi task system A race condition can occur if a task is interrupted between the call which sets error and when the task examin
92. abs and labs functions are builtins of gcc 5 18 4 3 double atof const char x __nptr The atof function converts the initial portion of the string pointed to by nptr to double representation It is equivalent to calling strtod nptr char NULL 5 18 4 4 int atoi const char x string Convert a string to an integer The atoi function converts the initial portion of the string pointed to by nptr to integer representation It is equivalent to int strtol nptr char NULL 10 except that atoi does not detect errors Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 60 5 18 4 5 long int atol const char string Convert a string to a long integer The atol function converts the initial portion of the string pointed to by st ringp to integer representation It is equivalent to strtol nptr char NULL 10 except that atol does not detect errors 5 18 4 6 void bsearch const void __key const void x __ base size_t __nmemb size_t __ size int __compar const void x const void The bsearch function searches an array of nmemb objects the initial member of which is pointed to by base for a member that matches the object pointed to by key The size of each member of the array is specified by size The contents of the array should be in ascending sorted order according to the compar ison function referenced by compar The compar rou
93. ages c c disable n1s make make install UN 117 17 Y YH Ur To save your self some download time you can alternatively download only the gcc core lt version gt tar bz2 and gcc c lt version gt tar bz2 parts of the gcc Also if you don t need C support you only need the core part and should only enable the C language support Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 8 Installing the GNU Tool Chain 167 Note Early versions of these tools did not support C The stdc libs are not included with C for AVR due to the size limitations of the devices 7 8 5 AVR Libc Warning You must install avr binutils avr gcc and make sure your path is set properly before installing avr libc Note If you have obtained the latest avr libc from cvs you will have to run the reconf script before using either of the build methods described below To build and install avr libc gunzip c avr libc lt version gt tar gz cd avr libc lt version gt doconf domake cd build make install UN 107 17 1 MH Ur Note The doconf script will automatically use the SPREFIX environment variable if you have set and exported it Alternatively you could do this shown for consistency with binutils and gcc gunzip c avr libe lt version gt tar gz tar xf cd avr libc lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install a Ur Ur UF UF Ur Ur
94. al28__ ror Don t know what kind of MCU you are compiling for Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 87 error need either COM1A1 or COMI1 endif enum UP DOWN volatile uint16_t pwm Note 1 volatile uint8_t direction SIGNAL SIG_OVERFLOW1 Note 2 switch direction Note 3 case UP if pwm 1023 direction DOWN break case DOWN if pwm 0 direction UP break OCR pwm Note 4 void ioinit void Note 5 tmrl is 10 bit PWM TCCRIA _BV PWM10 _BV PWM11 _BV XCOM11 tmrl running on full MCU clock TCCRIB _BV CS10 set PWM value to 0 OCR 0 enable OC1 and PB2 as output DDROC _BV OC1 timer_enable_int _BV TOIE1 enable interrupts sei int main void rinit G loop forever the interrupts are doing the rest for Note 6 r Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 88 return 0 5 23 3 Compiling and Linking This first thing that needs to be done is compile the source When compiling the compiler needs to know the processor type so the mmcu option is specified The Os option will tell the compiler to optimize the code for efficient space usage at the possible expense of code execution speed The g is used to embed debug info The debug
95. alc void asm CALCULATE Calling the function Calc will create assembler instructions to call the function CALCULATE 7 4 8 Links For a more thorough discussion of inline assembly usage see the gcc user manual The latest version of the gcc manual is always available here http gcc gnu org onlinedocs 7 5 Using malloc 7 5 1 Introduction On a simple device like a microcontroller implementing dynamic memory allocation 1s quite a challenge Many of the devices that are possible targets of avr libc have a minimal amount of RAM The smallest parts supported by the C environment come with 128 bytes of RAM This needs to be shared between initialized and uninitialized variables sections data and bss the dynamic memory allocator and the stack that is used for calling subroutines and storing local automatic variables Also unlike larger architectures there is no hardware supported memory management which could help in separating the mentioned RAM regions from being overwritten by each other The standard RAM layout is to place data variables first from the beginning of the internal RAM followed by bss The stack is started from the top of internal RAM growing downwards The so called heap available for the dynamic memory allocator will be placed beyond the end of bss Thus there s no risk that dynamic memory will ever collide with the RAM variables unless there were bugs in the implementation of the allocator
96. am execution contin ues as if the corresponding call of setimp had just returned the value __ ret Note longjmp cannot cause 0 to be returned If longjmp is invoked with a second argument of 0 1 will be returned instead Parameters __jmpb Information saved by a previous call to setjmp __ret Value to return to the caller of setjmp Returns This function never returns 5 15 2 2 int setjmp jmp_buf __jmpb Save stack context for non local goto include lt setjmp h gt setjmp saves the stack context environment in __jmpb for later use by longjmp The stack context will be invalidated if the function which called setjmp returns Parameters __jmpb Variable of type jmp_buf which holds the stack information such that the environment can be restored Returns setimp returns O if returning directly and non zero when returning from longjmp using the saved context Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 16 Standard Integer Types 40 5 16 Standard Integer Types 5 16 1 Detailed Description include lt stdint h gt Use ulintN_t if you need exactly N bits Since these typedefs are mandated by the C99 standard they are preferred over rolling your own typedefs Note If avr gcc s mint8 option is used no 32 bit types will be available for all ver sions of GCC below 3 5 8 bit types e typedef signed char int8_t typedef unsigned char uint8_t 16 bit types
97. aracter appears An E conversion uses the letter E rather than e to introduce the exponent The exponent always contains two digits if the value is zero the exponent is 00 fF The double argument is rounded and converted to decimal notation in the format ddd dda where the number of digits after the decimal point character is equal to the precision specification If the precision is missing it is taken as 6 if the precision is explicitly zero no decimal point character appears If a decimal point appears at least one digit appears before it gG The double argument is converted in style or e or F or E for G conver sions The precision specifies the number of significant digits If the precision is missing 6 digits are given if the precision is zero it is treated as 1 Style e is used if the exponent from its conversion is less than 4 or greater than or equal to the precision Trailing zeros are removed from the fractional part of the result a decimal point appears only if it is followed by at least one digit S Similar to the s format except the pointer is expected to point to a program memory ROM string instead of a RAM string In no case does a non existent or small field width cause truncation of a numeric field if the result of a conversion is wider than the field width the field is expanded to contain the conversion result Since the full implementation of all the mentioned features becomes fairly
98. ard E g applying the function strlen to a literal string will normally cause the compiler to immediately replace that call by the actual length of the string while with f freestanding it will always call strlen at run time e funsigned char Make any unqualfied char type an unsigned char Without this option they default to a signed char e funsigned bitfields Make any unqualified bitfield type unsigned By default they are signed e fshort enums Allocate to an enum type only as many bytes as it needs for the declared range of possible values Specifically the enum type will be equivalent to the smallest integer type which has enough room fpack struct Pack all structure members together without holes 7 10 2 Options for the assembler avr as 7 10 2 1 Machine specific assembler options e mmcu architecture e mmcu MCU name avr as understands the same mmcu options as avr gcc By default avr2 is assumed but this can be altered by using the appropriate arch pseudo instruction inside the assembler source file Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 177 e mall opcodes Turns off opcode checking for the actual MCU type and allows any possible AVR opcode to be assembled e mno skip bug Don t emit a warming when trying to skip a 2 word instruction with a CPSE SBIC SBIS SBRC SBRS instruction Early AVR devices suffered from a hardware bug
99. arice since avr gdb needs one of these to run as a a remote target backend 7 8 9 Simulavr Simulavr also uses the configure system so to build and install Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 9 Using the avrdude program 169 gunzip c simulavr lt version gt tar gz tar xf cd simulavr lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install Note You might want to have already installed avr binutils avr gcc and avr libc if you want to have the test programs built in the simulavr source 7 8 10 AVaRice Note These install notes are not applicable to avarice 1 5 or older You probably don t want to use anything that old anyways since there have been many improvements and bug fixes since the 1 5 release AVaRice also uses the configure system so to build and install gunzip c avarice lt version gt tar gz tar xf cd avarice lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install UN UN 107 UN UN 147 Ur Note AVaRice uses the bfd library for accessing various binary file formats You may need to tell the configure script where to find the lib and headers for the link to work This is usually done by invoking the configure script like this Replace lt hdr_path gt with the path to the b d h file on your system Replace lt 1ib_ path gt with the path to 1ibb d a on your system CPPFL
100. as 40 210 2 Typedef Documentation lt lt s cs pre o kod Se RES 41 Standard TO facilities o s so s cce a o SE Re 42 3 17 1 Detailed Description lt o crear erpresst 42 5 17 2 Define Documentation e ak e eere e ees 45 517 3 Function Documentation lt i ee 4 es sa e tee e eA 46 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen CONTENTS iii 5 18 320 5 21 ee 5 23 5 24 General utilities oie cis pt be e Ee eae 56 3 18 1 Detailed Descripfion e ee eos pss RA ee es 56 2 18 2 Defne Documentation ce 24 a ea kie optog BA Bes 58 5 18 3 Typedef Documentation c cs cas rip eee a 59 5 18 4 Function Documentation osoa e 59 5 18 5 Variable Documentation 67 bid ow ma ma a nepar 68 5 19 1 Detailed Description 2 2 ee ao a ees 68 5 19 2 Function Documentation lt e ae res seest 69 intemupts and Signals lt lt sopo na aa e SR E 76 5 20 1 Detailed Description lt ea ce eas 76 5 20 2 Define Documentation lt lt lt a a cere teessa 79 5 20 3 Function Documentation 264 4 re 4 0 Re 81 Special function register s sioe cacao wa SRS a aka 81 5 21 1 Detailed Description lt s soos A eR a 81 5 212 Define Documentation s oos c era o cerie bane un 82 DEMO PIRI 2 cora ee a ga ada ee E G 83 5 22 1 Detailed Description lt c eroaa 865 bee Ra 83 A simple POOJE E ia ee a E ee a a 84 Hi Te Piece 2 0 es SE edits BAM Es 84 ii gt dk goa
101. asm volatile sbi PORTB 0x07 you get a compilation error Error constant value required PORTB is a precompiler definition included in the processor specific file included in avr io h As you may know the precompiler will not touch strings and PORTB instead of 0x18 gets passed to the assembler One way to avoid this problem is Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 124 asm volatile sbi 0 0x07 I _SFR_IO_ADDR PORTB Note avr io h already provides a sbi macro definition which can be used in C pro grams Back to FAQ Index 7 3 11 Why does the PC randomly jump around when single stepping through my program in avr gdb When compiling a program with both optimization O and debug information g which is fortunately possible in avr gcc the code watched in the debugger is opti mized code While it is not guaranteed very often this code runs with the exact same optimizations as it would run without the g switch This can have unwanted side effects Since the compiler is free to reorder code ex ecution as long as the semantics do not change code is often rearranged in order to make it possible to use a single branch instruction for conditional operations Branch instructions can only cover a short range for the target PC 63 through 64 words from the current PC If a branch instruction cannot be used directly the compiler needs to work ar
102. ata Typically this includes access to the current timer counter value register TCNTn the input capture register ICRn and write access to the output compare registers OCRnM Refer to the actual datasheet for each device s set of registers that involves the TEMP register When accessing one of the registers that use TEMP from the main application and possibly any other one from within an interrupt routine care must be taken that no access from within an interrupt context could clobber the TEMP register data of an in progress transaction that has just started elsewhere To protect interrupt routines against other interrupt routines it s usually best to use the SIGNAL macro when declaring the interrupt function and to ensure that interrupts are still disabled when accessing those 16 bit timer registers Within the main program access to those registers could be encapsulated in calls to the cli and sei macros If the status of the global interrupt flag before accessing one of those registers is uncertain something like the following example code can be used uint16_t read_timerl void uint8_t sreg uint16_t val sreg SREG cli val TCNT1 SREG sreg return val Back to FAQ Index 7 3 10 How do I use a define d constant in an asm statement So you tried this asm volatile sbi 0x18 0x07 Which works When you do the same thing but replace the address of the port by its macro name like this
103. atan 34 atan2 34 ceil 34 cos 34 cosh 34 exp 34 fabs 34 floor 35 fmod 35 frexp 35 inverse 35 isinf 35 isnan 35 Idexp 35 log 35 log10 36 M_PI 33 M_SQRT2 33 modf 36 pow 36 sin 36 sinh 36 sqrt 36 square 36 tan 36 tanh 36 avr_parity parity_even_bit 17 avr_pgmspace memcpy_P 21 PGM_P 19 pgm_read_byte 19 pgm_read_byte_far 19 pgm_read_byte_near 20 pgm_read_dword 20 pgm_read_dword_far 20 pgm_read_dword_near 20 pgm_read_word 20 pgm_read_word_far 21 pgm_read_word_near 21 PGM_VOID_P 21 PSTR 21 strcasecmp_P 21 strcat_P 22 stremp_P 22 strepy_P 22 strlcat_P 22 strlcpy_P 23 strlen_P 23 strncasecmp_P 23 strncat_P 24 strncmp_P 24 strncpy_P 24 strnlen_P 24 avr_sfr _BV 81 bit_is_clear 82 bit_is_set 82 loop_until_bit_is_clear 82 loop_until_bit_is_set 82 avr_sleep set_sleep_mode 26 sleep_mode 26 avr_stdint int16_t 40 int32_t 40 int64_t 40 int8_t 40 intptr_t 40 uint16_t 40 uint32_t 40 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen sprintf 49 sprintf_P 49 sscanf 49 sscanf_P 49 stderr 44 stdin 45 stdout 45 ungetc 49 vfprintf 49 vfprintf_P 52 vfscanf 52 INDEX 183 uint64_t 40 vfscanf_P 54 uint8_t 40 vsnprintf 55 uintptr_t 40 vsnprintf_P 55 avr_stdio vsprintf 55 clearerr 45 vsprintf_P 55 EOF 44 avr_stdlib fclose 45 __compar_fn_t 58 fdevopen 45
104. avr libc Reference Manual 1 2 3 Generated by Doxygen 1 3 6 Tue Feb 15 16 09 51 2005 CONTENTS i Contents 1 AVR Libe 1 1 1 Supported Devices lt o oo be ea eA ee a 2 2 avr libc Module Index 21 avtlibeModul s oe aa a ek wee ee ee a Ee N 3 avr libc Data Structure Index 6 3 1 avr libc Data Structures oo ee ee eee eee 6 4 avr libc Page Index 4 1 ave libe Related Pa e 45 6 24 ea sde e a 6 5 avr libc Module Documentation 7 5 1 Bootloader Support Utilities 0 0 7 211 Detailed Description se oo essi Ge a eR oS 7 51 2 Define Documentation 2 65 est o eere ees 8 32 CRC COmputauons s coc eR Re a S 11 32 1 Detailed Description lt ad ce bb rides SR RES 11 5 2 2 Function Documentation 12 5 3 Busy wait delay loops 13 231 Detailed Description lt e ce ecc seses see ey Ai Res 13 53 2 Function Documentation xo Kees a eae as 14 34 EEPROM handing e ce oea le eS a ES 15 5 4 1 Detailed Description 15 5 4 2 Define Documentation oaoa 16 5 4 3 Function Documentation oaoa a 17 5 5 AVR device specific IO definitions osoo 17 30 Panty bit generalom or e be he eee Bee i Eee BEES 18 361 Detailed Description se lt 456s e535 4 oe Fe epee S 18 5 6 2 Define Documentation o os lt ssa reses erates 18 5 7 Program Space String Utilities aooaa 19 Generated on Tue Feb 15 16 09 56 2005 for avr lib
105. avr size program part of binutils coming from a Unix background doesn t account for the data initialization space added to the text section so in order to know how much flash the final program will consume one needs to add the values for both text and data but not bss while the amount of pre allocated SRAM is the sum of data and bss 7 72 The data Section This section contains static data which was defined in your code Things like the fol lowing would end up in data char err_str Your program has died a horrible death struct point pt 1 1 It is possible to tell the linker the SRAM address of the beginning of the data section This is accomplished by adding W1 Tdata addr to the avr gcc command used to the link your program Not that addr must be offset by adding 0x800000 the to real SRAM address so that the linker knows that the address is in the SRAM memory space Thus if you want the data section to start at 0x1100 pass 0x801100 at the address to the linker offset explained Note When using mal loc in the application which could even happen inside library calls additional adjustments are required 7 7 3 The bss Section Uninitialized global or static variables end up in the bss section 7 7 4 The eeprom Section This is where eeprom variables are stored 7 7 5 The noinit Section This sections is a part of the bss section What makes the noinit section special is that var
106. b and stabstr sections hold the debugging information and won t make it into the ROM file An even more useful option is S This option disassembles the binary file and inter sperses the source code in the output This method is much better in my opinion than using the S with the compiler because this listing includes routines from the libraries and the vector table contents Also all the fix ups have been satisfied In other words the listing generated by this option reflects the actual code that the processor will run Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project avr objdump h S demo elf gt demo lst Here s the output as saved in the demo 1st file demo elf file format elf32 avr Sections Idx Name Size VMA LMA File off 0 text 000000cc 00000000 00000000 00000094 CONTENTS ALLOC LOAD READONLY CODE 1 data 00000000 00800060 000000cc 00000160 CONTENTS ALLOC LOAD DATA 2 bss 00000003 00800060 00800060 00000160 ALLOC 3 noinit 00000000 00800063 00800063 00000160 CONTENTS 4 eeprom 00000000 00810000 00810000 00000160 CONTENTS 5 stab 000005d0 00000000 00000000 00000160 CONTENTS READONLY DEBUGGING 6 stabstr 000005c2 00000000 00000000 00000730 CONTENTS READONLY DEBUGGING Disassembly of section text 00000000 lt __vectors gt 0 Oa co rjmp 20 0x16 2 23 63 00 rjmp 198 Oxca 4 62 c0 rjmp 196 Oxca 6 61 c0 rjmp 194 Oxca 8 60 co
107. be utilized 7 2 2 Invoking the compiler For the purpose described in this document the assembler and linker are usually not invoked manually but rather using the C compiler frontend avr gcc that in turn will call the assembler and linker as required This approach has the following advantages Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 2 avr libc and assembler programs 113 e There is basically only one program to be called directly avr gcc regardless of the actual source language used The invokation of the C preprocessor will be automatic and will include the appropriate options to locate required include files in the filesystem The invokation of the linker will be automatic and will include the appropri ate options to locate additional libraries as well as the application start up code crt XXX o and linker script Note that the invokation of the C preprocessor will be automatic when the filename provided for the assembler file ends in S the capital letter s This would even apply to operating systems that use case insensitive filesystems since the actual decision is made based on the case of the filename suffix given on the command line not based on the actual filename from the file system Alternatively the language can explicitly be specified using the x assembler with cpp option 7 2 3 Example program The following annotated example features a simple 100 kHz square wave ge
108. c by Doxygen CONTENTS ii 5 8 5 9 Sul 5 12 513 5 14 5 7 1 Detailed Description lt lt cc seseo do 19 3142 Demme Documentaci n oe sses appa anpas se a 20 5 43 Function Documentation lt lt css E a 22 Additional notes from lt avr sfr_defs h gt 26 Power Management and Sleep Modes 27 59 1 Detailed Description s soe saci sins ee bees 27 5 9 2 Fun tion Documentation os s s 64 5 8 6 ewe es 27 Watchdog timer handling o o 28 5 10 1 Detailed Description lt se soe on socia a 28 5 10 2 Define Documentation oaoa 28 Character Operations lt lt se sce a A ent un 30 SILI Detailed Description so cerea be eA ee os 30 5 11 2 Fanciton Documentation e o o e lt s ap eacee a Ra 31 System Errors ENO eas Eor eb Gee R e a o 32 5 12 1 Detailed Description lt se soros esca ee GS 32 5122 Define Docunientation ooo baw as 33 Integer Type conversions s s coe soed eee ee ee ko eS 33 billi Me 33 5 14 1 Detaled Description gt ss cintas ea crese 33 5 14 2 Define Documentation s s e o e sace e a ee ea a 34 5 14 3 Function Documentation aoao 35 Setjmp and Longjmp ec sectes rro dediats t Eey 38 5 15 1 Detailed D scripti n lt o co se gao eepe Oe 38 5 15 2 Funcion Documentation os scs 66455 ee ee eR eS 39 Standard Integer Types ee teea dewe 40 5 16 1 Detailed Description gt lt lt cp RR A
109. c diagram If you have a development kit you should be able to use it rather than build the circuit for this project VCC MN IC1 R1 19 SCK PB7 Ba E LO RESET MISO PB6 I 20K a a c2 Gi 3 MOSI PB5 117 db Sai T H XTAL2 PB4 16 R2 D1 18pe E OCI PB3 gt AF XTALI PB2 bia See note 7 Na iL P 20 voc AIN1 PB1 13 END pa AINO PBO 2 Sa IcP PD6 HH T1 PD5 2 GND To PDA 8 INT1 PD3 H1 GND INTO PD2 H TxD PD1 H3 RXD PDO 4 AT90S2313P Figure 1 Schematic of circuit for demo project Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 85 The source code is given in demo c For the sake of this example create a file called demo c containing this source code Some of the more important parts of the code are Note 1 The PWM is being used in 10 bit mode so we need a 16 bit variable to remember the current value Note 2 SIGNAL is a macro that marks the function as an interrupt routine In this case the function will get called when the timer overflows Setting up interrupts is explained in greater detail in Interrupts and Signals Note 3 This section determines the new value of the PWM Note 4 Here s where the newly computed value is loaded into the PWM register Since we are in an interrupt routine it is safe to use a 16 bit assignment to the register Outside of an
110. ce Returns The strcpy_P function returns a pointer to the destination string dest Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 7 Program Space String Utilities 24 5 7 3 6 size_t strlcat_P char dst PGM_P size_t siz Concatenate two strings The strlcat_P function is similar to strlcat except that the src string must be located in program space flash Appends src to string dst of size siz unlike strncat siz is the full size of dst not space left At most siz 1 characters will be copied Always NULL terminates unless siz lt strlen dst Returns The strlcat_P function returns strlen src MIN siz strlen initial dst If retval gt siz truncation occurred 5 7 3 7 size_t strlepy_P char x dst PGM_P size_t siz Copy a string from progmem to RAM Copy src to string dst of size siz At most siz 1 characters will be copied Always NULL terminates unless siz 0 Returns The strlcpy_P function returns strlen src If retval gt siz truncation occurred 5 7 3 8 size_t strlen_P PGM_P src The strlen_P function is similar to strlen except that src is a pointer to a string in program space Returns The strlen function returns the number of characters in src 5 7 3 9 int strncasecmp_P const char x s1 PGM_P s2 size_t n Compare two strings ignoring case The strncasecmp_P function is similar to strcasecmp_P except it only compares the first n
111. cess the IO registers is not available It would be slower than using in out instructions anyway Since the operation to reload TCCNTO is time critical it is even performed before saving SREG Obviously this requires that the instructions involved would not change any of the flag bits in SREG Note 9 Interrupt routines must not clobber the global CPU state Thus it is usually necessary to save at least the state of the flag bits in SREG Note that this serves as an example here only since actually all the following instructions would not modify SREG either but that s not commonly the case Also it must be made sure that registers used inside the interrupt routine do not conflict with those used outside In the case of a RAM less device like the AT90S1200 this can only be done by agreeing on a set of registers to be used exclusively inside the interrupt routine there would not be any other chance to save a register anywhere If the interrupt routine is to be linked together with C modules care must be taken to follow the register usage guidelines imposed by the C compiler Also any register modified inside the interrupt sevice needs to be saved usually on the stack Note 10 As explained in Interrupts and Signals a global catch all interrupt handler that gets all unassigned interrupt vectors can be installed using the name __vector_ default This must be global and obviously should end in a ret i instr
112. change in a future release This file declares the standard IO facilities that are implemented in avr libc Due to the nature of the underlying hardware only a limited subset of standard IO is im plemented There is no actual file implementation available so only device IO can be performed Since there s no operating system the application needs to provide enough details about their devices in order to make them usable by the standard IO facilities Due to space constraints some functionality has not been implemented at all like some of the printf conversions that have been left out Nevertheless potential users of this implementation should be warned the printf and scanf families of functions although usually associated with presumably simple things like the famous Hello world program are actually fairly complex which causes their inclusion to eat up a fair amount of code space Also they are not fast due to the nature of interpreting the format string at run time Whenever possible resorting to the sometimes non standard predetermined conversion facilities that are offered by avr libc will usually cost much less in terms of speed and code size In order to allow programmers a code size vs functionality tradeoff the function vfprintf which is the heart of the printf family can be selected in different flavours using linker options See the documentation of vfprintf for a detailed description The same applies to vfscanf an
113. cision is zero no decimal point character appears If flags has the DTOSTRE_UPPERCASE bit set the letter E rather than e will be used to introduce the exponent The exponent always contains two digits if the value is zero the exponent is 00 If flags has the DTOSTRE_ALWAYS_SIGN bit set a space character will be placed into the leading position for positive numbers If flags has the DTOSTRE_PLUS_SIGN bit set a plus sign will be used instead of a space character in this case The dtostre function returns the pointer to the converted string s 5 18 4 10 char dtostrf double __val char __width char __prec char x __s The dtostrf function converts the double value passed in val into an ASCII repre sentationthat will be stored under s The caller is responsible for providing sufficient storage in s Conversion is done in the format d ddd The minimum field width of the output string including the and the possible sign for negative values is given in width and prec determines the number of digits after the decimal sign The dtostrf function returns the pointer to the converted string s 5 18 4 11 void exit int __ status The exit function terminates the application Since there is no environment to re turn to status is ignored and code execution will eventually reach an infinite loop thereby effectively halting all code processing In a C context global destructors will be called b
114. clobbers gives the compiler more freedom while optimizing your code 7 4 5 Assembler Macros In order to reuse your assembler language parts it is useful to define them as macros and put them into include files AVR Libc comes with a bunch of them which could be found in the directory avr include Using such include files may produce compiler warnings if they are used in modules which are compiled in strict ANSI mode To avoid that you can write __asm__ instead of asm and __volatile__ instead of volatile These are equivalent aliases Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 148 Another problem with reused macros arises if you are using labels In such cases you may make use of the special pattern which is replaced by a unique number on each asm statement The following code had been taken from avr include iomacros h define loop_until_bit_is_clear port bit __asm__ __volatile_ L_ sbic 0 1 Ant rjmp L_ no outputs I _SFR_IO_ADDR port I bit When used for the first time L_ may be translated to L_1404 the next usage might create L_1405 or whatever In any case the labels became unique too Another option is to use Unix assembler style numeric labels They are explained in How do I trace an assembler file in avr gdb The above example would then look like define loop_until_bit_is_clear port bit __asm__ _ _volatile__ I
115. cmp_P avr_pgmspace 21 strcat avr_string 70 strcat_P avr_pgmspace 22 strchr avr_string 70 strcmp avr_string 70 stremp_P avr_pgmspace 22 strcpy avr_string 70 strcpy_P Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen INDEX 189 avr_pgmspace 22 Strings 67 strlcat avr_string 71 strlcat_P avr_pgmspace 22 strlcpy avr_string 71 strlcpy_P avr_pgmspace 23 strlen avr_string 71 strlen_P avr_pgmspace 23 strlwr avr_string 71 strncasecmp avr_string 72 strncasecmp_P avr_pgmspace 23 strncat avr_string 72 strncat_P avr_pgmspace 24 strncmp avr_string 72 strncmp_P avr_pgmspace 24 strncpy avr_string 72 strncpy_P avr_pgmspace 24 strnlen avr_string 73 strnlen_P avr_pgmspace 24 strrchr avr_string 73 strrev avr_string 73 strsep avr_string 73 strstr avr_string 74 strtod avr_stdlib 63 strtok_r avr_string 74 strtol avr_stdlib 64 strtoul avr_stdlib 64 strupr avr_string 74 supported devices System Errors errno 31 tan avr_math 36 tanh avr_math 36 timer_enable_int avr_interrupts 80 toascii ctype 31 tolower ctype 31 tools optional 163 tools required 163 toupper ctype 31 uintl6_t avr_stdint 40 uint32_t avr_stdint 40 uint64_t avr_stdint 40 uint8_t avr_stdint 40 uintptr_t avr_stdint 40 ultoa avr_stdlib 65 ungetc avr_stdio 49 utoa avr_stdlib 66 vfp
116. cycles There is also an option to have devices using 10 bit addresses but that is not covered by this example Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 97 5 24 2 The TWI example project The ATmega TWI hardware supports both master and slave operation This example will only demonstrate how to use an AVR microcontroller as TWI master The imple mentation is kept simple in order to concentrate on the steps that are required to talk to a TWI slave so all processing is done in polled mode waiting for the TWI interface to indicate that the next processing step is due by setting the TWINT interrupt bit If it is desired to have the entire TWI communication happen in background all this can be implemented in an interrupt controlled way where only the start condition needs to be triggered from outside the interrupt routine There is a variety of slave devices available that can be connected to a TWI bus For the purpose of this example an EEPROM device out of the industry standard 24Cxx series has been chosen where xx can be one of 01 02 04 08 or 16 which are available from various vendors The choice was almost arbitrary mainly triggered by the fact that an EEPROM device is being talked to in both directions reading and writing the slave device so the example will demonstrate the details of both Usually there is probably not much need to add more EEPROM t
117. d the scanf family of functions The standard streams stdin stdout and stderr are provided but contrary to the C standard since avr libc has no knowledge about applicable devices these streams are not already pre initialized at application startup Also since there is no notion of file whatsoever to avr libc there is no function fopen that could be used to associate a stream to some device See note 1 Instead the function fdevopen is provided to associate a stream to a device where the device needs to provide a function to send a character to receive a character or both There is no differentiation between text and binary streams inside avr libc Character n is sent literally down to the device s put function If the device requires a carriage return r character to be sent before the linefeed its put routine must implement this see note 2 It should be noted that the automatic conversion of a newline character into a carriage return newline sequence breaks binary transfers If binary transfers are desired no automatic conversion should be performed but instead any string that aims to issue a CR LF sequence must use r n explicitly For convenience the first call to fdevopen that opens a stream for reading Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 43 will cause the resulting stream to be aliased to stdin Likewise the first call to fdevopen
118. ddress The address is in the program space 5 7 2 7 define pgm_read_dword_near address_short __LPM_ dword uint16_t address_short Read a double word from the program space with a 16 bit near address Note The address is a byte address The address is in the program space Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 7 Program Space String Utilities 22 5 7 2 8 define pgm_read_word address_short pgm_read_word_ near address_short Read a word from the program space with a 16 bit near address Note The address is a byte address The address is in the program space 5 7 2 9 define pgm_read_word_far address_long ELPM_word uint32_ t address_long Read a word from the program space with a 32 bit far address Note The address is a byte address The address is in the program space 5 7 2 10 define pgm_read_word_near address_short __ LPM_word uint16_ t address_short Read a word from the program space with a 16 bit near address Note The address is a byte address The address is in the program space 5 7 2 11 define PGM_VOID_P const prog_void x Used to declare a generic pointer to an object in program space 5 7 2 12 define PSTR s static char __c PROGMEM s _c 0 Used to declare a static pointer to a string in program space 5 7 3 Function Documentation 5 7 3 1 void x memcpy_P void x dest PGM_VOID_P src size_t n The memcpy_P funct
119. double atan double __x The atan function computes the principal value of the arc tangent of x The returned value is in the range 0 pi radians A domain error occurs for arguments not in the range 1 1 5 14 3 4 double atan2 double _ y double __x The atan2 function computes the principal value of the arc tangent of y x using the signs of both arguments to determine the quadrant of the return value The returned value is in the range pi pi radians If both x and y are zero the global variable errno is set to EDOM 5 14 3 5 double ceil double __x The ceil function returns the smallest integral value greater than or equal to x ex pressed as a floating point number 5 14 3 6 double cos double __x The cos function returns the cosine of x measured in radians 5 14 3 7 double cosh double __x The cosh function returns the hyperbolic cosine of x 5 14 3 8 double exp double _x The exp function returns the exponential value of x Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 14 Mathematics 36 5 14 3 9 double fabs double __x The fabs function computes the absolute value of a floating point number x 5 14 3 10 double floor double __x The floor function returns the largest integral value less than or equal to x expressed as a floating point number 5 14 3 11 double fmod double _ x double _ y The function fmod returns the floating point remaind
120. e Note that not all include files can be included into assembler sources Note 2 Assignment of registers to symbolic names used locally Another option would be to use a C preprocessor macro instead define work 16 Note 3 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 2 avr libc and assembler programs 115 Our bit number for the square wave output Note that the right hand side consists of a CPP macro which will be substituted by its value 6 in this case before actually being passed to the assembler Note 4 The assembler uses integer operations in the host defined integer size 32 bits or longer when evaluating expressions This is in contrast to the C compiler that uses the C type int by default in order to calculate constant integer expressions In order to get a 100 kHz output we need to toggle the PD6 line 200000 times per second Since we use timer 0 without any prescaling options in order to get the de sired frequency and accuracy we already run into serious timing considerations while accepting and processing the timer overflow interrupt the timer already continues to count When pre loading the TCCNTO register we therefore have to account for the number of clock cycles required for interrupt acknowledge and for the instructions to reload TCCNTO 4 clock cycles for interrupt acknowledge 2 cycles for the jump from the interrupt vector 2 cycles for the 2 instructions that reload TCCNTO
121. e JE Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWI 99 Note that the page size must be a power of two this simplifies the page boundary calculations below Ey define PAGE_SIZE 8 Saved TWI status register for error messages only We need to save it in a variable since the datasheet only guarantees the TWSR register to have valid contents while the TWINT bit in TWCR is set uint8_t twst Do all the startup time peripheral initializations UART for our debug test output and TWI clock el void ioinit void if F_CPU lt 1000000UL Note 4 Slow system clock double Baud rate to improve rate error UCSRA _BV U2X UBRR F_CPU 8 9600UL 1 9600 Bd else UBRR F_CPU 16 9600UL 1 9600 Bd endif UCSRB _BV TXEN tx enable initialize TWI clock 100 kHz clock TWPS 0 gt prescaler 1 if defined TWPS0O has prescaler megal28 amp newer TWSR 0 endif if F_CPU lt 3600000UL TWBR 10 smallest TWBR value see note 5 else TWBR F_CPU 100000UL 16 2 endif Note 6 Send character c down the UART Tx wait until tx holding register is empty a7 int uart_putchar char c if c An uart_putchar Xr loop_until_bit_is_set UCSRA UDRE Generated on Tue Feb 15 16 09 56 2005 for avr
122. e letter A in either upper or lower case represents 10 B represents 11 and so forth with Z representing 35 If endptr is not NULL strtoul stores the address of the first invalid character in endpt r If there were no digits at all however strtoul stores the original value of nptr in endptr Thus if npt r is not 10 but xxendptr is 0 on return the entire string was valid The strtoul function return either the result of the conversion or if there was a lead ing minus sign the negation of the result of the conversion unless the original non negated value would overflow in the latter case strtoul returns ULONG_MAX and errno is set to ERANGE If no conversion could be performed 0 is returned 5 18 4 29 char ultoa unsigned long int __val char x __s int __radix Convert an unsigned long integer to a string The function ultoa converts the unsigned long integer value from val into an ASCII representation that will be stored under s The caller is responsible for providing suf ficient storage in s Note The minimal size of the buffer s depends on the choice of radix For example if the radix is 2 binary you need to supply a buffer with a minimal length of 8 x sizeof unsigned long int 1 characters i e one character for each bit plus one for the string terminator Using a larger radix will require a smaller minimal buffer size Warning If the buffer is too small you risk
123. e pessimization due to the code increasement The only other optimization turned on with 03 is frename registers which could rather be enabled manually instead A simple O option is equivalent to O1 Note also that turning off all optimizations will prevent some warnings from being issued since the generation of those warnings depends on code analysis steps that are only performed when optimizing unreachable code unused variables See also the appropriate FAQ entry for issues regarding debugging optimized code e Wa assembler options e W1 linker options Pass the listed options to the assembler or linker respectively g Generate debugging information that can be used by avr gdb Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 176 e ffreestanding Assume a freestanding environment as per the C standard This turns off automatic builtin functions though they can still be reached by prepending __builtin_ to the actual function name It also makes the compiler not complain when main is declared with a void return type which makes some sense in a microcontroller environment where the application cannot meaningfully provide a return value to its environment in most cases main won t even return anyway However this also turns off all optimizations normally done by the compiler which assume that functions known by a certain name behave as described by the stand
124. e_t Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 69 e size_t strlen const char x __ATTR_PURE char x strlwr char x e int strncasecmp const char x const char x size_t __ ATTR_PURE char x strncat char x const char x size_t e int strncmp const char x const char x size_t _ ATTR_PURE char x strncpy char x const char x size_t e size_t strnlen const char x size_t __ATTR_PURE e char x strrchr const char x int __ATTR_PURE char x strrev char x e char x strsep char xx const char char x strstr const char x const char x __ ATTR_PURE char x strtok_r char x const char x char xx char x strupr char x 5 19 2 Function Documentation 5 19 2 1 void x memccpy void x dest const void x src int val size_t len Copy memory area The memccpy function copies no more than len bytes from memory area src to mem ory area dest stopping when the character val is found Returns The memccpy function returns a pointer to the next character in dest after val or NULL if val was not found in the first len characters of src 5 19 2 2 void x memchr const void x src int val size_t len Scan memory for a character The memchr function scans the first len bytes of the memory area pointed to by src for the character val The first byte to match val interpreted as an unsigned character stops the operation Returns The memchr
125. ed thus far from the input is stored through the next pointer which must be a pointer to int This is not a conversion although it can be suppressed with the x flag These functions return the number of input items assigned which can be fewer than provided for or even zero in the event of a matching failure Zero indicates that while there was input available no conversions were assigned typically this is due to an invalid input character such as an alphabetic character for a d conversion The value EOF is returned if an input failure occurs before any conversion such as an end of file occurs If an error or end of file occurs after conversion has begun the number of conversions which were successfully completed is returned By default all the conversions described above are available except the floating point conversions and the conversion These conversions will be available in the extended version provided by the library 1libscanf_f1t a Note that either of these conver sions requires the availability of a buffer that needs to be obtained at run time using malloc If this buffer cannot be obtained the operation is aborted returning the value EOF To link a program against the extended version use the following compiler flags in the link stage W1 u vfscanf lscanf_flt 1m A third version is available for environments that are tight on space This version is provided in the library 1ibscanf_min a and can be requested u
126. ed to the parameters passed via ap The format string fmt is scanned for conversion specifications Anything that doesn t comprise a conversion specification is taken as text that is matched literally against the input White space in the format string will match any white space in the data including none all other characters match only itself Processing is aborted as soon as the data and format string no longer match or there is an error or end of file condition on stream Most conversions skip leading white space before starting the actual conversion Conversions are introduced with the character Possible options can follow the e a x indicating that the conversion should be performed but the conversion result is to be discarded no parameters will be processed from ap e the character h indicating that the argument is a pointer to short int rather than int e the character 1 indicating that the argument is a pointer to long int rather than int for integer type conversions or a pointer to double for floating point conversions Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 54 In addition a maximal field width may be specified as a nonzero positive decimal integer which will restrict the conversion to at most this many characters from the input stream This field width is limited to at most 127 characters which is also the default value except for the c conversion tha
127. eeprom_is_ready bit_is_clear EECR EEWE Returns 1 if EEPROM is ready for a new read write operation 0 if not Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 5 AVR device specific IO definitions 17 5 4 3 Function Documentation 5 4 3 1 void eeprom_read_block void buf const void x addr size_t n Read a block of n bytes from EEPROM address addr to buf 5 4 3 2 uint8_t eeprom_read_byte const uint8_t addr Read one byte from EEPROM address addr 5 4 3 3 uint16_t eeprom_read_word const uint16_t x addr Read one 16 bit word little endian from EEPROM address addr 5 4 3 4 void eeprom_write_block const void buf void addr size_t n Write a block of n bytes to EEPROM address addr from buf 5 4 3 5 void eeprom_write_byte uint8_t x addr uint8_t val Write a byte val to EEPROM address addr 5 4 3 6 void eeprom_write_word uint16_t x addr uint16_t val Write a word val to EEPROM address addr 5 5 AVR device specific IO definitions include lt avr io h gt This header file includes the apropriate IO definitions for the device that has been spec ified by the mmcu compiler command line switch This is done by diverting to the appropriate file lt avr ioXXXX h gt which should never be included directly Some register names common to all AVR devices are defined directly within lt avr io h gt but most of the details come from the respective include file Note that this file always i
128. eet to see if it provides bootloader support Todo From email with Marek On smaller devices all except ATmega64 128 _ SPM_ REG is in the I O space accessible with the shorter in and out instructions since the boot loader has a limited size this could be an important optimization API Usage Example The following code shows typical usage of the boot API include lt inttypes h gt include lt avr interrupt h gt include lt avr pgmspace h gt void boot_program_page uint32_t page uint8_t buf uint16_t i uint8_t sreg Disable interrupts sreg SREG cli eeprom_busy_wait boot_page_erase page boot_spm_busy_wait Wait until the memory is erased for i 0 i lt SPM_PAGESIZE i 2 Set up little endian word uint16_t w buf w buf lt lt 8 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 1 Bootloader Support Utilities 8 boot_page_fill page i w boot_page_write page Store buffer in flash page boot_spm_busy_wait Wait until the memory is written Reenable RWW section again We need this if we want to jump back to the application after bootloading boot_rww_enable Re enable interrupts if they were ever enabled SREG sreg Defines 5 1 2 define BOOTLOADER_SECTION __attribute__ section bootloader define boot_spm_interrupt_enable _SPM_REG uint8_t _BV SPMIE define boot_spm
129. efault value of__malloc_margin is set to 32 7 5 4 Implementation details Dynamic memory allocation requests will be returned with a two byte header prepended that records the size of the allocation This is later used by free The returned address points just beyond that header Thus if the application accidentally writes before the returned memory region the internal consistency of the memory al locator is compromised The implementation maintains a simple freelist that accounts for memory blocks that have been returned in previous calls to free Note that all of this memory is considered to be successfully added to the heap already so no further checks against stack heap collisions are done when recycling memory from the freelist Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 5 Using malloc 154 The freelist itself is not maintained as a separate data structure but rather by modifying the contents of the freed memory to contain pointers chaining the pieces together That way no additional memory is reqired to maintain this list except for a variable that keeps track of the lowest memory segment available for reallocation Since both a chain pointer and the size of the chunk need to be recorded in each chunk the minimum chunk size on the freelist is four bytes When allocating memory first the freelist is walked to see if it could satisfy the request If there s a chunk available on the freelist that wi
130. efore halting execution 5 18 4 12 void free void __ptr The free function causes the allocated memory referenced by ptr to be made avail able for future allocations If ptr is NULL no action occurs 5 18 4 13 charx itoa int __val char x __ s int __radix Convert an integer to a string The function itoa converts the integer value from val into an ASCII representation that will be stored under s The caller is responsible for providing sufficient storage in S Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 62 Note The minimal size of the buffer s depends on the choice of radix For example if the radix is 2 binary you need to supply a buffer with a minimal length of 8 x sizeof int 1 characters i e one character for each bit plus one for the string terminator Using a larger radix will require a smaller minimal buffer size Warning If the buffer is too small you risk a buffer overflow Conversion is done using the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a If radix is 10 and val is negative a minus sign will be prepended The itoa function returns the pointer passed as s 5 18 4 14 long labs long __i The labs function computes the absolute value of the long integer i Note The abs and labs functions are builtins of gcc 5 18 4
131. el before since it then takes this label as the name of a new function that appears to have been entered Thus the best practice to avoid this confusion is to only use non local labels when declaring a new function and restrict anything else to local labels Local labels consist just of a number only References to these labels consist of the number followed by the letter b for a backward reference or f for a forward reference These local labels may be re used within the source file references will pick the closest label with the same number and given direction Example myfunc push r16 push rl7 push r18 push YL push YH eor r16 rl6 start loop ldi YL lo8 sometable 1di YH hi8 sometable rjmp E jump to loop test at end Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 126 IRS ld r17 Y loop continues here breq WE return from myfunc prematurely inc r16 2 cmp rl6 18 brlo 1b jump back to top of loop al pop YH pop YL pop r18 pop r17 pop r16 ret Back to FAQ Index 7 3 13 How do I pass an IO port as a parameter to a function Consider this example code include lt inttypes h gt include lt avr io h gt void set_bits_func_wrong volatile uint8_t port uint8_t mask port mask void set_bits_func_correct volatile uint8_t port uint8_t mask port mask define set_bits_macro port mask port mask int main
132. ent it can only be used to jump to a label in the same local function In order to jump directly to another non local function the C library provides the setjmp and longjmp functions setjmp and longjmp are useful for dealing with errors and interrupts encountered in a low level subroutine of a program Note setimp and longjmp make programs hard to understand and maintain If possi ble an alternative should be used longjmp can destroy changes made to global register variables see How to per manently bind a variable to a register For a very detailed discussion of setimp longjmp see Chapter 7 of Advanced Pro gramming in the UNIX Environment by W Richard Stevens Example include lt setjmp h gt jmp_buf env int main void i if setjmp env handle error main processing loop which calls foo some where void foo void blah blah blah if err longjmp env 1 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 15 Setjmp and Longjmp 39 Functions int setimp mp_buf __jmpb void longjmp jmp_buf __jmpb int __ret __ATTR_NORETURN__ 5 15 2 Function Documentation 5 15 2 1 void longjmp jmp_buf __jmpb int __ret Non local jump to a saved stack context include lt setjmp h gt longjmp restores the environment saved by the last call of setimp with the corre sponding __jmpb argument After longjmp is completed progr
133. ents 5 17 3 38 int vsprintf_P char x __s const char x __fmt va_list ap Variant of vsprintf that uses a fmt string that resides in program memory 5 18 General utilities 5 18 1 Detailed Description include lt stdlib h gt This file declares some basic C macros and functions as defined by the ISO standard plus some AVR specific extensions Data Structures struct div_t struct ldiv_t Non standard i e non ISO C functions define RANDOM_MAX 0x7FFFFFFF e char x itoa int __val char __s int __radix e char x ltoa long int __val char __s int __radix Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 57 char x utoa unsigned int __ val char x__s int __radix char x ultoa unsigned long int __val char x__s int __ radix long random void void srandom unsigned long __ seed long random_r unsigned long ctx Conversion functions for double arguments Note that these functions are not located in the default library 1ibc a but in the mathematical library 1 ilbm a So when linking the application the 1m option needs to be specified define DTOSTR_ALWAYS_SIGN 0x01 x put or for positives define DTOSTR_PLUS_SIGN 0x02 x put rather than x define DTOSTR_UPPERCASE 0x04 x put E rather e x char x dtostre double __val char x__s unsigned char __prec unsigned char __ flags char x dtostrf double _
134. er of x y 5 14 3 12 double frexp double __value int x __exp The frexp function breaks a floating point number into a normalized fraction and an integral power of 2 It stores the integer in the int object pointed to by exp The frexp function returns the value x such that x is a double with magnitude in the interval 1 2 1 or zero and value equals x times 2 raised to the power x exp If value is zero both parts of the result are zero 5 14 3 13 double inverse double The function inverse returns 1 x Note This function does not belong to the C standard definition 5 14 3 14 int isinf double __x The function isinf returns 1 if the argument x is either positive or negative infinity otherwise 0 5 14 3 15 int isnan double __x The function isnan returns 1 if the argument x represents a not a number NaN object otherwise 0 5 14 3 16 double Idexp double __x int __ exp The Idexp function multiplies a floating point number by an integral power of 2 The Idexp function returns the value of x times 2 raised to the power exp If the resultant value would cause an overflow the global variable errno is set to ERANGE and the value NaN is returned Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 14 Mathematics 37 5 14 3 17 double log double __x The log function returns the natural logarithm of argument x If the argument is less than or equal 0 a domain error will
135. erhaps rounds up the current time to the next sec ond when calculating the timestamp of an updated file in case the current time cannot be represented in FAT s terms this causes a situation where make sees a file coming from the future Since all make decisions are based on file timestamps and their dependencies make warns about this situation Solution don t use inferior file systems operating systems Neither Unix file systems nor HPFS aka NTFS do experience that problem Workaround after saving the file wait a second before starting make Or simply ignore the warning If you are paranoid execute a make clean all to make sure everything gets rebuilt In networked environments where the files are accessed from a file server this message can also happen if the file server s clock differs too much from the network client s clock In this case the solution is to use a proper time keeping protocol on both sys tems like NTP As a workaround synchronize the client s clock frequently with the server s clock Back to FAQ Index Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 137 7 3 25 Why are many interrupt flags cleared by writing a logical 1 Usually each interrupt has its own interrupt flag bit in some control register indicating the specified interrupt condition has been met by representing a logical in the respec tive bit position When working with
136. es errno If another task changes errno during this time the result will be incorrect for the interrupted task Defines define EDOM 33 define ERANGE 34 5 12 2 Define Documentation 5 12 2 1 define EDOM 33 Domain error 5 12 2 2 define ERANGE 34 Range error 5 13 Integer Type conversions include lt inttypes h gt This header file includes the exact width integer definitions from lt stdint h gt and extends them with additional facilities provided by the implementation 5 14 Mathematics 5 14 1 Detailed Description include lt math h gt This header file declares basic mathematics constants and functions Note In order to access the functions delcared herein it is usually also required to addi tionally link against the library 1ibm a See also the related FAQ entry Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 14 Mathematics 34 Defines define M_PI 3 141592653589793238462643 e define M_SQRT2 1 4142135623730950488016887 Functions double cos double __x _ ATTR_CONST double fabs double __x _ ATTR_CONST double fmod double __x double __y _ ATTR_CONST double modf double __ value double __iptr double sin double __x _ ATTR_CONST double sqrt double __x _ ATTR_CONST double tan double __x _ ATTR_CONST double floor double __ x _ ATTR_CONST double ceil double __x _ ATTR_CONST double frexp double __ value int __exp double Idexp double __x i
137. estions 122 Constructors and destructors are supported though including global ones When programming C in space and runtime sensitive environments like microcon trollers extra care should be taken to avoid unwanted side effects of the C calling conventions like implied copy constructors that could be called upon function invo cation etc These things could easily add up into a considerable amount of time and program memory wasted Thus casual inspection of the generated assembler code using the S compiler option seems to be warranted Back to FAQ Index 7 3 8 Shouldn t I initialize all my variables Global and static variables are guaranteed to be initialized to 0 by the C standard avr gcc does this by placing the appropriate code into section init4 see The initN Sections With respect to the standard this sentence is somewhat simplified because the standard allows for machines where the actual bit pattern used differs from all bits being 0 but for the AVR target in general all integer type variables are set to 0 all pointers to a NULL pointer and all floating point variables to 0 0 As long as these variables are not initialized i e they don t have an equal sign and an initialization expression to the right within the definition of the variable they go into the bss section of the file This section simply records the size of the variable but otherwise doesn t consume space neither within the object fi
138. evice signature 0xle9101 avrdude gt The command displays a list of valid commands avrdude gt gt gt gt Valid commands dump dump memory dump lt memtype gt lt addr gt lt N Bytes gt read alias for dump write write memory write lt memtype gt lt addr gt lt b1 gt lt b2 gt lt bN gt erase perform a chip erase sig display device signature bytes part display the current part information send send a raw command send lt b1 gt lt b2 gt lt b3 gt lt b4 gt help help ES help quit quit Use the part command to display valid memory types for use with the dump and write commands avrdude gt 7 10 Using the GNU tools This is a short summary of the AVR specific aspects of using the GNU tools Normally the generic documentation of these tools is fairly large and maintained in texinfo files Command line options are explained in detail in the manual page 7 10 1 Options for the C compiler avr gcc 7 10 1 1 Machine specific options for the AVR The following machine specific options are recognized by the C compiler frontend mmcu architecture Compile code for architecture Currently known architectures are Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 172 avrl Simple CPU core only assembler support avr2 Classic CPU core up to 8 KB of ROM avr3 Classic CPU core more
139. f bak rm rf 1lst map EXTRA_CLEAN_FILES lst PRG 1st S lst elf OBJDUMP h S lt gt Rules for building the text rom images text hex bin srec hex PRG hex bin PRG bin srec PRG srec elf OBJCOPY j text j data O ihex lt sa hex oo srec elf S OBJCOPY j text j data O srec lt oo bin elf S OBJCOPY j text j data O binary lt Se Rules for building the eeprom rom images eeprom ehex ebin esrec ehex PRG _eeprom hex ebin PRG _eeprom bin esrec PRG _eeprom srec o _eeprom hex elf S OBJCOPY j S_eeprom srec elf S OBJCOPY j _eeprom bin elf S OBJCOPY j eeprom c eeprom c eeprom c Every thing below here is used by the casual user FIG2DEV fig2dev hange section lma hange section lma hange section lma eeprom 0 O eeprom 0 O eeprom 0 0O by avr libc s build system and ihex lt S srec lt binary lt a can be ignored Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 96 EXTRA_CLEAN_FILES hex bin srec dox eps png pdf eps PRG eps png PRG png pdf PRG pdf eps fig S FIG2DEV L eps lt e pdt fig S FIG2DEV L pdf lt png fig FIG2DEV L png lt SG 5 24 Example using the two wire interface TWI Some
140. fforts we wouldn t have a terrific free set of tools to develop AVR projects We all owe thanks to The GCC Team which produced a very capable set of development tools for an amazing number of platforms and processors Denis Chertykov denisc overta ru for making the AVR specific changes to the GNU tools Denis Chertykov and Marek Michalkiewicz marekm linux org pl for developing the standard libraries and startup code for AVR GCC Uros Platise for developing the AVR programmer tool uisp Joerg Wunsch joerg FreeBSD ORG for adding all the AVR development tools to the FreeBSD http www freebsd org ports tree and for pro viding the basics for the demo project Brian Dean bsdtbsdhome com for developing avrdude an alternative to uisp and for contributing documentation which describes how to use it Avr dude was previously called avrprog Eric Weddington eric evcohs com for maintaining the WinAVR pack age and thus making the continued improvements to the Opensource AVR toolchain available to many users Rich Neswold for writing the original avr tools document which he graciously allowed to be merged into this document and his improvements to the demo project Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 2 avr libc and assembler programs 112 Theodore A Roth for having been a long time maintainer of many of the tools AVR Libc the AVR port of GDB AVaRICE uisp avrdude
141. g Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 7 Program Space String Utilities 19 teor 0 __tmp_reg__ n t mov __tmp_reg__ 0 n t lsr zo mne lsr so AVE eor 0 __tmp_reg__ r _t 0 unsigned char val 2 ro i _t 1 gt gt 1 1 Returns 1 if val has an odd number of bits set 5 7 Program Space String Utilities 5 7 1 Detailed Description tinclude lt avr io h gt tinclude lt avr pgmspace h gt POLO E IO IAEA GF The functions in this module provide interfaces for a program to access data stored in program space flash memory of the device In order to use these functions the target device must support either the LPM or ELPM instructions Note These functions are an attempt to provide some compatibility with header files that come with TAR C to make porting applications between different compilers easier This is not 100 compatibility though GCC does not have full support for multiple address spaces yet If you are working with strings which are completely based in ram use the stan dard string functions described in Strings If possible put your constant tables in the lower 64K and use pgm_read_byte_ near or pgm_read_word_near instead of pgm_read_byte_far or pgm_read_ word_far since it is more efficient that way and you can still use the upper 64K for executable code Defines e define PSTR s static
142. g if rv lt 0 error printf Wrote d bytes n rv for a 0 a lt 256 printf s 04x a rv ee24xx_read_bytes a 16 b if rv lt 0 error LE hy 16 printf warning short read d n rv a rv for x 0 x lt rv x printf 02x b x putchar n printf done n Note 1 The header file lt compat twi h gt contains some macro definitions for symbolic constants used in the TWI status register These definitions match the names used in the Atmel datasheet except that all names have been prefixed with TW_ Note 2 The clock is used in timer calculations done by the compiler for the UART baud rate and the TWI clock rate Note 3 The address assigned for the 24Cxx EEPROM consists of 1010 in the upper four bits The following three bits are normally available as slave sub addresses allowing to Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 107 operate more than one device of the same type on a single bus where the actual sub address used for each device is configured by hardware strapping However since the next data packet following the device selection only allows for 8 bits that are used as an EEPROM address devices that require more than 8 address bits 24C04 and above steal subaddress bits and use them for the EEPROM cell address bits 9 to 11 as re quired This example s
143. gister r0 w Special upper register r24 r26 r28 r30 pairs x Pointer register pair X X 127 126 y Pointer register pair Y y 129 r28 Z Pointer register pair Z z r31 r30 These definitions seem not to fit properly to the AVR instruction set The author s as sumption is that this part of the compiler has never been really finished in this version but that assumption may be wrong The selection of the proper contraint depends on the range of the constants or registers which must be acceptable to the AVR instruction they are used with The C compiler doesn t check any line of your assembler code But it is able to check the constraint against your C expression However if you specify the wrong constraints then the compiler may silently pass wrong code to the assem bler And of course the assembler will fail with some cryptic output or internal errors For example if you specify the constraint r and you are using this register with an ori instruction in your assembler code then the compiler may select any register This will fail if the compiler chooses r2 to r15 It will never choose r0 or r1 because these are uses for special purposes That s why the correct constraint in that case is d On the other hand if you use the constraint M the compiler will make sure that you don t pass anything else but an 8 bit value Later on we will see how to pass multibyte expression results to the assembler code The followi
144. gisters listed above are defined 5 20 2 4 define INTERRUPT signame Value void signame void __attribute__ interrupt void signame void include lt avr signal h gt Introduces an interrupt handler function that runs with global interrupts initially en abled This allows interrupt handlers to be interrupted 5 20 2 5 define sei __asm volatile__ sei include lt avr interrupt h gt Enables interrupts by clearing the global interrupt mask This function actually com piles into a single line of assembly so there is no function call overhead 5 20 2 6 define SIGNAL signame Value void signame void __attribute__ signal void signame void include lt avr signal h gt Introduces an interrupt handler function that runs with global interrupts initially dis abled Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 21 Special function registers 81 5 20 3 Function Documentation 5 20 3 1 _ inline void timer_enable_int unsigned char ints static include lt avr interrupt h gt This function modifies the timsk register The value you pass via ints is device specific 5 21 Special function registers 5 21 1 Detailed Description When working with microcontrollers many of the tasks usually consist of controlling the peripherals that are connected to the device respectively programming the subsys tems that are contained in the controller which by itself c
145. he delimiter character or NULL if the end of the string was reached is stored in string An empty field i e one caused by two adjacent delimiter characters can be detected by comparing the location referenced by the pointer returned in string to 0 Returns The strtok_r function returns a pointer to the original value of string If xstringp is initially NULL strsep returns NULL 5 19 2 24 char x strstr const char s1 const char s2 Locate a substring The strstr function finds the first occurrence of the substring s2 in the string s1 The terminating 0 characters are not compared Returns The strstr function returns a pointer to the beginning of the substring or NULL if the substring is not found If s2 points to a string of zero length the function returns sl 5 19 2 25 char x strtok_r char x string const char delim char xx last Parses the string s into tokens strtok_r parses the string s into tokens The first call to strtok_r should have string as its first argument Subsequent calls should have the first argument set to NULL If a token ends with a delimiter this delimiting character is overwritten with a 10 and a pointer to the next character is saved for the next call to strtok_r The delimiter string delim may be different for each call last is a user allocated char pointer It must be the same while parsing the same string strtok_r is a reentrant version of strtok Returns
146. he new size value whatever is less will be identical to the contents of the old region even in case a new region had to be allocated It is acceptable to pass ptr as NULL in which case realloc will behave identical to malloc If the new memory cannot be allocated realloc returns NULL and the region at pt r will not be changed 5 18 4 24 void srand unsigned int __seed Pseudo random number generator seeding see rand 5 18 4 25 void srandom unsigned long __seed Pseudo random number generator seeding see random 5 18 4 26 double strtod const char x __nptr char xx __endptr The strtod function converts the initial portion of the string pointed to by nptr to double representation Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 65 The expected form of the string is an optional plus or minus sign followed by a sequence of digits optionally containing a decimal point character op tionally followed by an exponent An exponent consists of an E or e followed by an optional plus or minus sign followed by a sequence of digits Leading white space characters in the string are skipped The strtod function returns the converted value if any If endptr is not NULL a pointer to the character after the last character used in the conversion is stored in the location referenced by endpt r If no conversion is performed zero is returned and the
147. her intterupt define enable_external_int mask __EICR mask e __inline__ void timer_enable_int unsigned char ints Macros for writing interrupt handler functions e define SIGNAL signame define INTERRUPT signame e define EMPTY_INTERRUPT signame 5 20 2 Define Documentation 5 20 2 1 define cli __asm volatile__ cli include lt avr interrupt h gt Disables all interrupts by clearing the global interrupt mask This function actually compiles into a single line of assembly so there is no function call overhead 5 20 2 2 define EMPTY_INTERRUPT signame Value void signame void __attribute__ naked void signame void __asm__ __volatile__ reti Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 20 Interrupts and Signals 80 include lt avr signal h gt Defines an empty interrupt handler function This will not generate any prolog or epilog code and will only return from the ISR Do not define a function body as this will define it for you Example EMPTY_INTERRUPT SIG_ADC 5 20 2 3 define enable_external_int mask _EICR mask include lt avr interrupt h gt This macro gives access to the GIMSK register or EIMSK register if using an AVR Mega device or GICR register for others Although this macro is essentially the same as assigning to the register it does adapt slightly to the type of device being used This macro is unavailable if none of the re
148. hrough the C preprocessor first and have the assem bler generate line number debugging information for it the following command can be used S avr gcc c x assembler with cpp o foo o foo S Wa gstabs Note that on Unix systems that have case distinguishing file systems specifying a file name with the suffix S upper case letter S will make the compiler automatically assume x assembler with cpp while using s would pass the file directly to the assembler no preprocessing done 7 10 3 Controlling the linker avr 1d 7 10 3 1 Selected linker options While there are no machine specific options for avr ld a number of the standard options might be of interest to AVR users lname Locate the archive library named libname a and use it to resolve currently unresolved symbols from it The library is searched along a path that con sists of builtin pathname entries that have been specified at compile time e g usr local avr lib on Unix systems possibly extended by pathname entries as specified by L options that must precede the 1 options on the command line e Lpath Additional location to look for archive libraries requested by 1 options e defsym symbol expr Define a global symbol symbol using expr as the value M Print a linker map to stdout Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 179 e Map mapfile Print a linker map to mapfile e cref
149. iables and heap If dynamic memory should be placed in external RAM while keeping the variables in internal RAM something like the following could be used Note that for demonstration Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 5 Using malloc 153 purposes the assignment of the various regions has not been made adjacent in this example so there are holes below and above the heap in external RAM that remain completely unaccessible by regular variables or dynamic memory allocations shown in light bisque color in the picture below avr gcc Wl defsym __heap_start 0x802000 defsym __heap_end 0x803fff external RAM 8 xs s u ir amp on board RAM ZE k oo o o o SP 1 __malloc_heap_end __heap_end RAMEND brkval _ bss end _ malloc_heap_start __heap_start _ data _end __ bss start data start Figure 4 Internal RAM variables and stack external RAM heap If__malloc_heap_endis 0 the allocator attempts to detect the bottom of stack in order to prevent a stack heap collision when extending the actual size of the heap to gain more space for dynamic memory It will not try to go beyond the current stack limit decreased by __malloc_margin bytes Thus all possible stack frames of interrupt routines that could interrupt the current function plus all further nested function calls must not require more stack space or they will risk colliding with the data segment The d
150. iables which are defined as such int foo __attribute__ section noinit Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 7 Memory Sections 160 will not be initialized to zero during startup as would normal bss data Only uninitialized variables can be placed in the noinit section Thus the following code will cause avr gcc to issue an error int bar __attribute__ section noinit Oxaa It is possible to tell the linker explicitly where to place the noinit section by adding W1 section start noinit 0x802000 to the avr gcc command line at the linking stage For example suppose you wish to place the noinit section at SRAM address 0x2000 avr gcc Wl section start noinit 0x802000 Note Because of the Harvard architecture of the AVR devices you must manually add 0x800000 to the address you pass to the linker as the start of the section Oth erwise the linker thinks you want to put the noinit section into the text section instead of data bss and will complain Alternatively you can write your own linker script to automate this FIXME need an example or ref to dox for writing linker scripts 7 7 6 The initN Sections These sections are used to define the startup code from reset up through the start of main These all are subparts of the text section The purpose of these sections is to allow for more specific placement of code within your program Note
151. ication The ATmegal28 ships with the fuse enabled that turns this device into AT mega103 compatibility mode This means that some ports are not fully usable and in particular that the internal SRAM is located at lower addresses Since by default the stack is located at the top of internal SRAM a program compiled for an ATmega128 running on such a device will immediately crash upon the first function call or rather upon the first function return Devices with a JTAG interface have the JTAGEN fuse programmed by default This will make the respective port pins that are used for the JTAG interface un available for regular IO Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 134 Back to FAQ Index 7 3 20 Why do all my foo bar strings eat up the SRAM By default all strings are handled as all other initialized variables they occupy RAM even though the compiler might warn you when it detects write attempts to these RAM locations and occupy the same amount of flash ROM so they can be initialized to the actual string by startup code The compiler can optimize multiple identical strings into a single one but obviously only for one compilation unit i e a single C source file That way any string literal will be a valid argument to any C function that expects a const char x argument Of course this is going to waste a lot of SRAM In Program Space String Utilities a
152. imization First there s no universal definition for better with optimization often being a speed vs code size tradeoff See the detailed discus sion for which option affects which part of the code generation A test case was run on an ATmega128 to judge the effect of compiling the library itself using different optimization levels The following table lists the results The test case consisted of around 2 KB of strings to sort Test 1 used qsort using the standard library stremp test 2 used a function that sorted the strings by their size thus had two calls to strlen per invocation When comparing the resulting code size it should be noted that a floating point version of fvprintf was linked into the binary in order to print out the time elapsed which is entirely not affected by the different optimization levels and added about 2 5 KB to the code Optimization Size of text Time for test 1 Time for test 2 flags 03 6898 903 us 19 7 ms 02 6666 972 us 20 1 ms Os 6618 955 us 20 1 ms Os 6474 972 us 20 1 ms mcall prologues The difference between 955 us and 972 us was just a single timer tick so take this with a grain of salt So generally it seems Os mcall prologues is the most universal best opti mization level Only applications that need to get the last few percent of speed benefit from using 03 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen
153. imply assumes all subaddress bits are 0 for the smaller devices so the EO El and E2 inputs of the 24Cxx must be grounded Note 4 For slow clocks enable the 2 x U SJART clock multiplier to improve the baud rate error This will allow a 9600 Bd communication using the standard 1 MHz calibrated RC oscillator See also the Baud rate tables in the datasheets Note 5 The datasheet explains why a minimum TWBR value of 10 should be maintained when running in master mode Thus for system clocks below 3 6 MHz we cannot run the bus at the intented clock rate of 100 kHz but have to slow down accordingly Note 6 This function is used by the standard output facilities that are utilized in this example for debugging and demonstration purposes Note 7 In order to shorten the data to be sent over the TWI bus the 24Cxx EEPROMs support multiple data bytes transfered within a single request maintaining an internal address counter that is updated after each data byte transfered successfully When reading data one request can read the entire device memory if desired the counter would wrap around and start back from 0 when reaching the end of the device Note 8 When reading the EEPROM a first device selection must be made with write intent R W bit set to 0 indicating a write operation in order to transfer the EEPROM ad dress to start reading from This is called master transmitter mode Each completion of a particular step in TWI
154. info is useful for disassemblies and doesn t end up in the hex files so I usually specify it Finally the c tells the compiler to compile and stop don t link This demo is small enough that we could compile and link in one step However real world projects will have several modules and will typically need to break up the building of the project into several compiles and one link avr gcc g Os mmcu at90s2333 c demo c The compilation will create a demo o file Next we link it into a binary called demo elf avr gcc g mmcu at90s2333 o demo elf demo o It is important to specify the MCU type when linking The compiler uses the mmcu option to choose start up files and run time libraries that get linked together If this option isn t specified the compiler defaults to the 8515 processor environment which is most certainly what you didn t want 5 23 4 Examining the Object File Now we have a binary file Can we do anything useful with it besides put it into the processor The GNU Binutils suite is made up of many useful tools for manipulating object files that get generated One tool is avr objdump which takes information from the object file and displays it in many useful ways Typing the command by itself will cause it to list out its options For instance to get a feel of the application s size the h option can be used The output of this option shows how much space is used in each of the sections the sta
155. ing malloc The amount of stack required for your application cannot be determined that easily For example if you recursively call a function and forget to break that recursion the amount of stack required is infinite You can look at the generated assembler code avr gcc S there s a comment in each generated assembler file that tells Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 136 you the frame size for each generated function That s the amount of stack required for this function you have to add up that for all functions where you know that the calls could be nested Back to FAQ Index 7 3 23 Is it really impossible to program the ATtinyXX in C While some small AVRs are not directly supported by the C compiler since they do not have a RAM based stack and some do not even have RAM at all itis possible anyway to use the general purpose registers as a RAM replacement since they are mapped into the data memory region Bruce D Lightner wrote an excellent description of how to do this and offers this together with a toolkit on his web page http lightner net avr ATtinyAvrGcc html Back to FAQ Index 7 3 24 What is this clock skew detected messsage It s a known problem of the MS DOS FAT file system Since the FAT file system has only a granularity of 2 seconds for maintaining a file s timestamp and it seems that some MS DOS derivative Win9x p
156. ing passed in fmt The actual values to print are passed as a variable argument list ap vfprintf returns the number of characters written to stream or EOF in case of an error Currently this will only happen if st ream has not been opened with write intent The format string is composed of zero or more directives ordinary characters not which are copied unchanged to the output stream and conversion specifications each of which results in fetching zero or more subsequent arguments Each conversion Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 51 specification is introduced by the character The arguments must properly correspond after type promotion with the conversion specifier After the the following appear in sequence Zero or more of the following flags The value should be converted to an alternate form For c d i s and u conversions this option has no effect For o conversions the precision of the number is increased to force the first character of the output string to a zero except if a zero value is printed with an explicit precision of zero For x and X conversions a non zero result has the string Ox or OX for X conversions prepended to it 0 zero Zero padding For all conversions the converted value is padded on the left with zeros rather than blanks If a precision is given with a numeric conversion d i 0 u i x and X
157. instruction and it is clear that only this single interrupt request bit will be cleared There is no need to perform a read modify write cycle like an SBI instruction since all bits in these control registers are interrupt bits and writing a logical 0 to the remaining bits as it is done by the simple OUT instruction will not alter them so there is no risk of any race condition that might accidentally clear another interrupt request bit So instead of writing TIFR _BV TOVO wrong simply use TIFR _BV TOVO Back to FAQ Index 7 3 26 Why have programmed fuses the bit value 0 Basically fuses are just a bit in a special EEPROM area For technical reasons erased E E PROM cells have all bits set to the value 1 so unprogrammed fuses also have a logical 1 Conversely programmed fuse cells read out as bit value 0 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 138 Back to FAQ Index 7 3 27 Which AVR specific assembler operators are available See Pseudo ops and operators Back to FAQ Index 7 4 Inline Asm AVR GCC Inline Assembler Cookbook About this Document The GNU C compiler for Atmel AVR RISC processors offers to embed assembly language code into C programs This cool feature may be used for manually optimizing time critical parts of the software or to use specific processor instruction which are not available in the C language Because of a lack of documentati
158. interrupt the assignment should only be performed with interrupts disabled if there s a chance that an interrupt routine could also access this register or another register that uses TEMP see the appropriate FAQ entry Note 5 This routine gets called after a reset It initializes the PWM and enables interrupts Note 6 The main loop of the program does nothing all the work is done by the interrupt routine If this was a real product we d probably put a SLEEP instruction in this loop to conserve power Note 7 Early AVR devices saturate their outputs at rather low currents when sourcing cur rent so the LED can be connected directly the resulting current through the LED will be about 15 mA For modern parts at least for the ATmega 128 however Atmel has drastically increased the IO source capability so when operating at 5 V Vcc R2 is needed Its value should be about 150 Ohms When operating the circuit at 3 V it can still be omitted though 5 23 2 The Source Code THE BEER WARE LICENSE Revision 42 lt joerg FreeBSD ORG gt wrote this file As long as you retain this notice you can do whatever you want with this stuff If we meet some day and you think Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 86 A A A A FH in in in in this stuff is worth it you can buy me a beer in return Joerg Wunsch Simple AVR demonstration
159. interrupt handlers this interrupt flag bit usually gets cleared automatically in the course of processing the interrupt sometimes by just calling the handler at all sometimes e g for the U SJART by reading a particular hardware register that will normally happen anyway when processing the interrupt From the hardware s point of view an interrupt is asserted as long as the respective bit is set while global interrupts are enabled Thus it is essential to have the bit cleared before interrupts get re enabled again which usually happens when returning from an interrupt handler Only few subsystems require an explicit action to clear the interrupt request when using interrupt handlers The notable exception is the TWI interface where clearing the interrupt indicates to proceed with the TWI bus hardware handshake so it s never done automatically However if no normal interrupt handlers are to be used or in order to make extra sure any pending interrupt gets cleared before re activating global interrupts e g an external edge triggered one it can be necessary to explicitly clear the respective hardware interrupt bit by software This is usually done by writing a logical 1 into this bit position This seems to be illogical at first the bit position already carries a logical 1 when reading it so why does writing a logical to it clear the interrupt bit The solution is simple writing a logical to it requires only a single OUT
160. ion is similar to memcpy except the src string resides in pro gram space Returns The memcpy_P function returns a pointer to dest Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 7 Program Space String Utilities 23 5 7 3 2 int strcasecmp_P const char x s1 PGM_P s2 Compare two strings ignoring case The strcasecmp_P function compares the two strings sl and s2 ignoring the case of the characters Parameters sl A pointer to a string in the devices SRAM s2 A pointer to a string in the devices Flash Returns The strcasecmp_P function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 5 7 3 3 char x strcat_P char dest PGM_P src The strcat_P function is similar to strcat except that the src string must be located in program space flash Returns The strcat function returns a pointer to the resulting string dest 5 7 3 4 int stremp_P const char x s1 PGM_P s2 The stremp_P function is similar to stremp except that s2 is pointer to a string in program space Returns The stremp_P function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 5 7 3 5 char x strepy_P char dest PGM_P src The strcpy_P function is similar to strcpy except that src is a pointer to a string in program spa
161. ion will always return a false value 5 17 3 5 int ferror FILE x __ stream Test the error flag of stream This flag can only be cleared by a call to clearerr 5 17 3 6 int fgetc FILE x __ stream The function fgetc reads a character from st ream It returns the character or EOF in case end of file was encountered or an error occurred The routines feof or ferror must be used to distinguish between both situations 5 17 3 7 char fgets char x __ str int __size FILE x __stream Read at most size 1 bytes from st ream until a newline character was encoun tered and store the characters in the buffer pointed to by str Unless an error was encountered while reading the string will then be terminated with a NUL character If an error was encountered the function returns NULL and sets the error flag of stream which can be tested using ferror Otherwise a pointer to the string will be returned Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 48 5 17 3 8 int fprintf FILE x __ stream const char __fmt The function fprintf performs formatted output to stream See vfprintf for details 5 17 3 9 int fprintf_P FILE x __ stream const char __fmt Variant of fprintf that uses a fmt string that resides in program memory 5 17 3 10 int fputc int __c FILE __stream The function fputc sends the character c though given as type int to strea
162. l ldd r22 Y 33 0x21 84 Ja al ldd r23 Y 34 0x22 86 ce 01 movw r24 r28 88 01 96 adiw r24 0x01 1 8a Oc dod reall 24 Oxa4 This will finally copy the ROM string into the local buffer buf Variable p located at Y 33 is read and passed together with the address of buf Y 1 to strepy_P This will copy the string from ROM to buf Note that when using a compile time constant index omitting the first step reading the pointer from ROM via memcpy_P usually remains unnoticed since the compiler would then optimize the code for accessing array at compile time Back to FAQ Index 7 3 16 How to use external RAM Well there is no universal answer to this question it depends on what the external RAM is going to be used for Basically the bit SRE SRAM enable in the MCUCR register needs to be set in order to enable the external memory interface Depending on the device to be used and the application details further registers affecting the external memory operation like XMCRA and XMCRB and or further bits in MCUCR might be configured Refer to the datasheet for details If the external RAM is going to be used to store the variables from the C program i e the data and or bss segment in that memory area it is essential to set up the external memory interface early during the device initialization so the initialization of these variable will take place Refer to How to modify MCUCR or WDTCR early for a description h
163. large three different flavours of vfprintf can be selected using linker options The default vf printf implements all the mentioned functionality except floating point conversions A minimized version of vfprintf is available that only implements the very basic in teger and string conversion facilities but none of the additional options that can be Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 53 specified using conversion flags these flags are parsed correctly from the format spec ification but then simply ignored This version can be requested using the following compiler options Wl u vfprintf iprintf_min If the full functionality including the floating point conversions is required the follow ing options should be used WIl u viprintf lprintf_flt Im Limitations The specified width and precision can be at most 127 For floating point conversions trailing digits will be lost if a number close to DBL_MAX is converted with a precision gt 0 5 17 3 32 int vfprintf_P FILE x _ stream const char __fmt va_list __ap Variant of vfprintf that uses a fmt string that resides in program memory 5 17 3 33 int vfscanf FILE x __ stream const char x _ fmt va_list __ap Formatted input This function is the heart of the scanf family of functions Characters are read from st ream and processed in a way described by fmt Conver sion results will be assign
164. le nor within flash memory Of course being a variable it will consume space in the target s SRAM In contrast global and static variables that have an initializer go into the data section of the file This will cause them to consume space in the object file in order to record the initializing value and in the flash ROM of the target device The latter is needed since the flash ROM is the only way that the compiler can tell the target device the value this variable is going to be initialized to Now if some programmer wants to make doubly sure their variables really get a 0 at program startup and adds an initializer just containing 0 on the right hand side they waste space While this waste of space applies to virtually any platform C is implemented on it s usually not noticeable on larger machines like PCs while the waste of flash ROM storage can be very painful on a small microcontroller like the AVR So in general variables should only be explicitly initialized if the initial value is non Zero Back to FAQ Index 7 3 9 Why do some 16 bit timer registers sometimes get trashed Some of the timer related 16 bit IO registers use a temporary register called TEMP in the Atmel datasheet to guarantee an atomic access to the register despite the fact that Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 123 two separate 8 bit IO transfers are required to actually move the d
165. ler requires to setup the counter register pair Thus at a CPU speed of 1 MHz delays of up to about 262 1 milliseconds can be achieved 5 3 2 3 inline__ void _delay_ms double _ms static Perform a delay of __ms milliseconds using _delay_loop_2 The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency in Hertz Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 4 EEPROM handling 15 The maximal possible delay is 262 14 ms F_CPU in MHz 5 3 2 4 inline__ void _delay_us double _us static Perform a delay of __us microseconds using _delay_loop_1 The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency in Hertz The maximal possible delay is 768 us F_CPU in MHz 5 4 EEPROM handling 5 4 1 Detailed Description include lt avr eeprom h gt This header file declares the interface to some simple library routines suitable for han dling the data EEPROM contained in the AVR microcontrollers The implementation uses a simple polled mode interface Applications that require interrupt controlled EEPROM access to ensure that no time will be wasted in spinloops will have to deploy their own implementation Note All of the read write functions first make sure the EEPROM is ready to be ac cessed Since this may cause long delays if a write operation is still pending time critical applications should first poll the EEPROM e
166. less siz lt strlen dst Returns The strlcat function returns strlen src MIN siz strlen initial dst If retval gt siz truncation occurred 5 19 2 13 size_t strlcpy char x dst const char x src size_t siz Copy a string Copy src to string dst of size siz At most siz 1 characters will be copied Always NULL terminates unless siz 0 Returns The strlcpy function returns strlen src If retval gt siz truncation occurred 5 19 2 14 size_t strlen const char x src Calculate the length of a string The strlen function calculates the length of the string src not including the terminat ing 0 character Returns The strlen function returns the number of characters in src Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 73 5 19 2 15 char x strlwr char x string Convert a string to lower case The strlwr function will convert a string to lower case Only the upper case alphabetic characters A Z are converted Non alphabetic characters will not be changed Returns The strlwr function returns a pointer to the converted string 5 19 2 16 int strncasecmp const char x s1 const char x s2 size_t len Compare two strings ignoring case The strncasecmp function is similar to strcasecmp except it only compares the first n characters of sl Returns The strncasecmp function returns an integer less than equal to or greater than zero if sl
167. lete before enabling the RWW mameory 5 1 2 13 define boot_spm_busy _SPM_REG amp uint8_t _BV SPMEN Check if the SPM instruction is busy 5 1 2 14 define boot_spm_busy_wait do while boot_spm_busy Wait while the SPM instruction is busy 5 1 2 15 define boot_spm_interrupt_disable _SPM_REG amp uint8_t _ BV SPMIE Disable the SPM interrupt 5 1 2 16 define boot_spm_interrupt_enable _SPM_REG uint8_t _ BV SPMIE Enable the SPM interrupt 5 1 2 17 define BOOTLOADER SECTION _ attribute__ section boot loader Used to declare a function or variable to be placed into a new section called boot loader This section and its contents can then be relocated to any address such as the bootloader NRWW area at link time 5 2 CRC Computations 5 2 1 Detailed Description include lt avr crc16 h gt This header file provides a optimized inline functions for calculating 16 bit cyclic re dundancy checks CRC using common polynomials References Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 2 CRC Computations 12 See the Dallas Semiconductor app note 27 for 8051 assembler example and general CRC optimization suggestions The table on the last page of the app note is the key to understanding these implementations Jack Crenshaw s Impementing CRCs article in the January 1992 isue of Embed ded Systems Programming This may be difficult to find but it ex
168. libc by Doxygen 5 24 Example using the two wire interface TWD 100 UDR c return 0 Note 7 Read len bytes from EEPROM starting at eeaddr into buf This requires two bus cycles during the first cycle the device will be selected master transmitter mode and the address transfered Address bits exceeding 256 are transfered in the E2 E1 E0 bits subaddress bits of the device selector The second bus cycle will reselect the device repeated start condition going into master receiver mode and transfer the data from the device to the TWI master Multiple bytes can be transfered by ACKing the client s transfer The last transfer will be NACKed which the client will take as an indication to not initiate further transfers int ee24xx_read_bytes uint16_t eeaddr int len uint8_t buf E E EEC i E E JE E a OE uint8_t sla twcr n 0 int rv 0 patch high bits of EEPROM address into SLA sla TWI_SLA_24CXX eeaddr gt gt 8 amp 0x07 lt lt 1 Note 8 First cycle master transmitter mode restart if n gt MAX_ITER return 1 begin TWCR _BV TWINT _BV TWSTA _BV TWEN send start condition while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_REP_START OK but should not happen case TW_START break case TW_MT_ARB_LOST Note 9 goto begin default return 1 er
169. list Checks are first made whether the tail chunk is large enough to hold a chunk of its own at all otherwise realloc will simply do nothing and return the original region When growing the region it is first checked whether the existing allocation can be ex tended in place If so this is done and the original pointer is returned without copying any data contents As a side effect this check will also record the size of the largest chunk on the freelist If the region cannot be extended in place but the old chunk is at the top of heap and the above freelist walk did not reveal a large enough chunk on the freelist to satisfy the new request an attempt is made to quickly extend this topmost chunk and thus the heap so no need arises to copy over the existing data If there s no more space available in the heap same check is done as in malloc the entire request will fail Otherwise malloc will be called with the new request size the existing data will be copied over and free will be called on the old region Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 6 Release Numbering and Methodology 155 7 6 Release Numbering and Methodology 7 6 1 Release Version Numbering Scheme 7 6 1 1 Stable Versions A stable release will always have a minor number that is an even number This implies that you should be able to upgrade to a new version of the library with the same major and minor numbers without fear tha
170. little knowledge to the public in the hope to get enough response to improve this document Feel free to contact the author via e mail For the latest release check http www ethernut de Herne 17th of May 2002 Harald Kipp harald kipp at egnite de Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 139 Note As of 26th of July 2002 this document has been merged into the documentation for avr libc The latest version is now available at http savannah nongnu org projects avr libc 7 4 1 GCC asm Statement Let s start with a simple example of reading a value from port D asm in 0 1 r value I _SFR_IO_ADDR PORTD Each asm statement is devided by colons into up to four parts 1 The assembler instructions defined as a single string constant in 0 1 2 A list of output operands separated by commas Our example uses just one r value 3 A comma separated list of input operands Again our example uses one operand only I _SFR_IO_ADDR PORTD 4 Clobbered registers left empty in our example You can write assembler instructions in much the same way as you would write assem bler programs However registers and constants are used in a different way if they refer to expressions of your C program The connection between registers and C operands is specified in the second and third part of the asm instruction the list of input and output operands respectively
171. ll fit the request exactly it will be taken disconnected from the freelist and returned to the caller If no exact match could be found the closest match that would just satisfy the request will be used The chunk will normally be split up into one to be returned to the caller and another smaller one that will remain on the freelist In case this chunk was only up to two bytes larger than the request the request will simply be altered internally to also account for these additional bytes since no separate freelist entry could be split off in that case If nothing could be found on the freelist heap extension is attempted This is where _ malloc_margin will be considered if the heap is operating below the stack or where __malloc_heap_end will be verified otherwise If the remaining memory is insufficient to satisfy the request NULL will eventually be returned to the caller When calling free a new freelist entry will be prepared An attempt is then made to aggregate the new entry with possible adjacent entries yielding a single larger entry available for further allocations That way the potential for heap fragmentation is hopefully reduced A call to realloc first determines whether the operation is about to grow or shrink the current allocation When shrinking the case is easy the existing chunk is split and the tail of the region that is no longer to be used is passed to the standard free function for insertion into the free
172. m It returns the character or EOF in case an error occurred 5 17 3 11 int fputs const char x __ str FILE x __ stream Write the string pointed to by str to stream st ream Returns 0 on success and EOF on error 5 17 3 12 int fputs_P const char x __str FILE x __ stream Variant of fputs where st r resides in program memory 5 17 3 13 size_t fread void x _ ptr size_t __size size_t __nmemb FILE x _ stream Read nmemb objects size bytes each from st ream to the buffer pointed to by ptr Returns the number of objects successfully read i e nmemb unless an input error occured or end of file was encountered feof and ferror must be used to distinguish between these two conditions 5 17 3 14 int fscanf FILE x __ stream const char x __fmt The function f scanf performs formatted input reading the input data from st ream See vfscanf for details 5 17 3 15 int fscanf_P FILE x __ stream const char x _ fmt Variant of fscanf using a fmt string in program memory 5 17 3 16 size_t fwrite const void __ptr size_t __size size_t __nmemb FILE x _ stream Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 49 Write nmemb objects size bytes each to stream The first byte of the first object is referenced by ptr Returns the number of objects successfully written i e nmemb unless an output error occured 5 17 3 17 char gets char __st
173. ments where most of the jumps would go to the default label they might waste a bit of flash memory e mshort calls Use rjmp rcall limited range on gt 8K devices On avr2 and avr4 architec tures less than 8 KB or flash memory this is always the case On avr3 and avr5 architectures calls and jumps to targets outside the current function will by default use jmp call instructions that can cover the entire address range but that require more flash ROM and execution time e mrtl Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 175 Dump the internal compilation result called RTL into comments in the generated assembler code Used for debugging avr gcc e msize Dump the address size and relative cost of each statement into comments in the gen erated assembler code Used for debugging avr gcc e mdeb Generate lots of debugging information to stderr 7 10 1 2 Selected general compiler options The following general gcc options might be of some interest to AVR users On Optimization level n Increasing n is meant to optimize more an optimization level of O means no optimization at all which is the default if no O option is present The special option Os is meant to turn on all 02 optimizations that are not expected to increase code size Note that at 03 gcc attempts to inline all simple functions For the AVR target this will normally constitute a larg
174. mmand line would cause the linker to place the data segment at address 0x2000 in the SRAM avr gcc mmcu atmegal28 o foo out W1 Tdata 0x802000 See the explanation of the data section for why 0x800000 needs to be added to the ac tual value Note that unless a minit stack option has been given when compiling the C source file that contains the function main the stack will still remain in inter nal RAM through the symbol __ stack that is provided by the run time startup code This is probably a good idea anyway since internal RAM access is faster and even required for some early devices that had hardware bugs preventing them from using a stack in external RAM Note also that the heap for malloc will still be placed after all the variables in the data section so in this situation no stack heap collision can occur 7 11 Todo List Group avr_boot From email with Marek On smaller devices all except AT mega64 128 _ SPM_REG is in the I O space accessible with the shorter in and out instructions since the boot loader has a limited size this could be an important optimization Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen Index PATH 162 PREFIX 162 prefix 162 _BV avr_sfr 81 _EEGET avr_eeprom 15 _EEPUT avr_eeprom 15 _ compar_fn_t avr_stdlib 58 _ malloc_heap_end avr_stdlib 66 _ malloc_heap_start avr_stdlib 66 _ malloc_margin avr_stdlib 67 _crc16_update avr_crc 11 _crc_cci
175. mode function See the data sheet for your device for more details Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 10 Watchdog timer handling 28 5 10 Watchdog timer handling 5 10 1 Detailed Description include lt avr wdt h gt This header file declares the interface to some inline macros handling the watchdog timer present in many AVR devices In order to prevent the watchdog timer configura tion from being accidentally altered by a crashing application a special timed sequence is required in order to change it The macros within this header file handle the required sequence automatically before changing any value Interrupts will be disabled during the manipulation Note Depending on the fuse configuration of the particular device further restrictions might apply in particular it might be disallowed to turn off the watchdog timer Defines define wdt_reset __asm volatile__ wdr define wdt_disable define wdt_enable timeout _wdt_write timeout define WDTO_15MS 0 define WDTO_30MS 1 define WDTO_60MS 2 define WDTO_120MS 3 define WDTO_250MS 4 define WDTO_500MS 5 define WDTO_IS 6 define WDTO_2S 7 5 10 2 Define Documentation 5 10 2 1 define wdt_disable Value __asm__ _ volatile__ in tmp_reg__ SREG__ n t out 0 BLU Mne A out 0 _ zero_reg__ Ant out SREG__ __tmp_reg__ Ante no outputs I _SFR_IO_ADDR _WD_CON
176. mple If it isn t the assembler will complain I O address out of range 0 0x3f so this should be fairly safe If you do not define __ SFR_OFF SET so it will be 0x20 by default all special register addresses are defined as memory addresses so SREG is 0x5f and if code size and speed are not important and you don t like the ugly if above you can always use lds sts to access them But this will not work if _ SFR_OFFSET 0x20 so use a different macro defined only if __ SFR_OF FSET 0x20 for safety sts _SFR_ADDR SPMCR r24 In C programs all 3 combinations of _SFR_ASM_COMPAT and ___SFR_OFF SET are supported the _SFR_ADDR SPMCR macro can be used to get the address of the SPMCR register 0x57 or 0x68 depending on device 5 9 Power Management and Sleep Modes 5 9 1 Detailed Description include lt avr sleep h gt Use of the SLEEP instruction can allow your application to reduce it s power com sumption considerably AVR devices can be put into different sleep modes Refer to the datasheet for the details relating to the device you are using Sleep Functions void set_sleep_mode uint8_t mode void sleep_mode void 5 9 2 Function Documentation 5 9 2 1 void set_sleep_mode uint8_t mode Select a sleep mode 5 9 2 2 void sleep_mode void Put the device in sleep mode How the device is brought out of sleep mode depends on the specific mode selected with the set_sleep_
177. ncludes include lt avr sfr_defs h gt See Special function registers for the details Included are definitions of the IO register set and their respective bit values as specified in the Atmel documentation Note that Atmel is not very consistent in its naming conventions so even identical functions sometimes get different names on different devices Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 6 Parity bit generation 18 Also included are the specific names useable for interrupt function definitions as docu mented here Finally the following macros are defined 5 6 RAMEND A constant describing the last on chip RAM location XRAMEND A constant describing the last possible location in RAM This is equal to RA MEND for devices that do not allow for external RAM E2END A constant describing the address of the last EEPROM cell FLASHEND A constant describing the last byte address in flash ROM SPM_PAGESIZE For devices with bootloader support the flash pagesize in bytes to be used for the SPM instruction Parity bit generation 5 6 1 Detailed Description include lt avr parity h gt This header file contains optimized assembler code to calculate the parity bit for a byte Defines define parity_even_bit val 5 6 2 Define Documentation 5 6 2 1 define parity_even_bit val Value unsigned char _ t _asm_ mov _ tmp_reg_ 50 n t swap 20 n t O O
178. nerator using an AT90S1200 clocked with a 10 7 MHz crystal Pin PD6 will be used for the square wave output include lt avr io h gt Note 1 work 16 Note 2 tmp 17 inttmp 19 intsav 0 SQUARE PD6 Note 3 Note 4 tmconst 10700000 200000 100 kHz gt 200000 edges s fuzz 8 clocks in ISR until TCNTO is set section text global main Note 5 main rcall ioinit T3 rjmp lb Note 6 global SIG_OVERFLOWO Note 7 SIG_OVERFLOWO idi inttmp 256 tmconst fuzz Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 2 avr libc and assembler programs 114 out in sbic rjmp sbi rjmp lo cbi out reti Lloinit sbi Iar out Tai out ldi out sei ret FR_IO_ADD intsav _SF FR_IO_ADD FR_IO_ADD FR_IO_ADD FR_IO_ADD FR_IO_ADD work _BV T S FR_IO_ADD work _BV C S FR_IO_ADD work 256 S FR_IO_ADD R ICNTO R PORTD R PORTD R PORTD R SREG R DDRD OIEO R TIMSK S00 R TCCRO tmconst R TCNTO global __vector_default __vector_default reti end Note 1 int R_IO_ADDR SREG SQU SQU SQU ints SQUA wor wor wor tmp ARE ARE ARE av RE K tmr0 Note 8 Note 9 CK 1 Note 10 As in C programs this includes the central processor specific file containing the IO port definitions for the devic
179. ng table shows all AVR assembler mnemonics which require operands and the related contraints Because of the improper constraint definitions in version 3 3 they aren t strict enough There is for example no constraint which restricts integer Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 143 constants to the range 0 to 7 for bit set and bit clear operations Mnemonic Constraints Mnemonic Constraints adc rr add rr adiw wl and rr andi d M asr r belr I bld rI brbc Llabel brbs Llabel bset I bst rI cbi LI cbr dl com r cp rr cpc rr cpi d M cpse rr dec r elpm tz eor rr in rI inc r ld re Idd rb ldi d M Ids r label lpm bz Isl r Isr r mov rr movw rr mul rr neg r or rr ori d M out Lr pop r push r rol r ror r sbe rr sbci d M sbi LI sbic LI sbiw wl sbr d M sbre rn sbrs rI ser d st e r std b r sts label r sub rr subi d M swap r Constraint characters may be prepended by a single constraint modifier Contraints without a modifier specify read only operands Modifiers are Modifier Specifies Write only operand usually used for all output operands Read write operand not supported by inline assembler amp Register should be used for output only Output operands must be write only and the C expression result must be an lvalue which mea
180. ns that the operands must be valid on the left side of assignments Note that the compiler will not check if the operands are of reasonable type for the kind of operation used in the assembler instructions Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 144 Input operands are you guessed it read only But what if you need the same operand for input and output As stated above read write operands are not supported in inline assembler code But there is another solution For input operators it is possible to use a single digit in the constraint string Using digit n tells the compiler to use the same register as for the n th operand starting with zero Here is an example asm volatile swap 0 r value 0 value This statement will swap the nibbles of an 8 bit variable named value Constraint 0 tells the compiler to use the same input register as for the first operand Note however that this doesn t automatically imply the reverse case The compiler may choose the same registers for input and output even if not told to do so This is not a problem in most cases but may be fatal if the output operator is modified by the assembler code before the input operator is used In the situation where your code depends on different registers used for input and output operands you must add the amp constraint modifier to your output operand The following example demonstrates this problem asm
181. nt __exp __ATTR_CONST double exp double _x _ ATTR_CONST double cosh double __x _ ATTR_CONST double sinh double __x _ ATTR_CONST double tanh double __x _ ATTR_CONST double acos double __x _ ATTR_CONST double asin double __x _ ATTR_CONST double atan double __x _ ATTR_CONST double atan2 double __y double __x _ ATTR_CONST double log double __x _ ATTR_CONST double log10 double __x _ ATTR_CONST double pow double __x double __y _ ATTR_CONST int isnan double __x _ ATTR_CONST int isinf double __x _ ATTR_CONST double square double __x __ ATTR_CONST double inverse double _ ATTR_CONST 5 14 2 Define Documentation 5 14 2 1 define M_PI 3 141592653589793238462643 The constant pi 5 14 2 2 define M_SQRT2 1 4142135623730950488016887 The square root of 2 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 14 Mathematics 35 5 14 3 Function Documentation 5 14 3 1 double acos double __x The acos function computes the principal value of the arc cosine of x The returned value is in the range 0 pi radians A domain error occurs for arguments not in the range 1 1 5 14 3 2 double asin double __x The asin function computes the principal value of the arc sine of x The returned value is in the range 0 pi radians A domain error occurs for arguments not in the range 1 1 5 14 3 3
182. o an ATmega system that way the smallest possible AVR device that offers hardware TWI support is the ATmega8 which comes with 512 bytes of EEPROM which is equivalent to an 24C04 device The ATmegal28 already comes with twice as much EEPROM as the 24C16 would offer One exception might be to use an externally connected EEPROM device that is removable e g SDRAM PC memory comes with an integrated TWI EEPROM that carries the RAM configuration information 5 24 3 The Source Code PH mk at nos A abonosa A Banh ah nina da ap Se ee een E E THE BEER WARE LICENSE Revision 42 lt joerg FreeBSD ORG gt wrote this file As long as you retain this notice you can do whatever you want with this stuff If we meet some day and you think this stuff is worth it you can buy me a beer in return Joerg Wunsch MS Stee SS Ee eS eS ee Se eee SS ee ee ee ee ee Se SSE Soe eee ee See Se SS E Id twitest c v 1 2 2 2 2005 02 07 22 47 46 arcanum Exp Simple demo program that talks to a 24Cxx ISC EEPROM using the builtin TWI interface of an ATmega device io include lt inttypes h gt include lt stdio h gt include lt stdlib h gt include lt avr io h gt include lt compat twi h gt Note 1 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWI 98 define DEBUG 1 System clock in Hz KLA define F_CPU 14745600UL Note 2
183. o get a new AVR developer up to speed quickly using the freely available development tools binutils gcc avr libc and many others If you find yourself stuck on a problem which this document doesn t quite address you may wish to post a message to the avr gcc mailing list Most of the developers of the AVR binutils and gcc ports in addition to the devleopers of avr libc subscribe to the list so you will usually be able to get your problem resolved You can subscribe to the list at http www avrl org mailman listinfo avr gcc list Before posting to the list you might want to try reading the Frequently Asked Ques tions chapter of this document Note This document is a work in progress As such it may contain in correct information If you find a mistake please send an email to avr libc dev nongnu org describing the mistake Also send us an email if you find that a specific topic is missing from the document 1 1 Supported Devices The following is a list of AVR devices currently supported by the library AT90S Type Devices at90s1200 1 at90s2313 at90s2323 at90s2333 at90s2343 at90s4414 at90s4433 at90s4434 at90s8515 at90c8534 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 1 1 Supported Devices e at90s8535 at90can128 ATmega Type Devices atmega8 atmega 103 atmega128 atmega16 atmega161 atmega162 atmega163 atmegal65 atmegal68 atmega169 atmega32
184. of a fixed size string The strnlen function returns the number of characters in the string pointed to by src not including the terminating 0 character but at most len In doing this strnlen looks only at the first len characters at src and never beyond src len Returns The strnlen function returns strlen src if that is less than len or len if there is no O character among the first len characters pointed to by src 5 19 2 21 char x strrchr const char x src int val Locate character in string The strrchr function returns a pointer to the last occurrence of the character val in the string src Here character means byte these functions do not work with wide or multi byte characters Returns The strrchr function returns a pointer to the matched character or NULL if the character is not found 5 19 2 22 char x strrev char string Reverse a string The strrev function reverses the order of the string Returns The strrev function returns a pointer to the beginning of the reversed string Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 75 5 19 2 23 char strsep char xx string const char delim Parse a string into tokens The strsep function locates in the string referenced by string the first occurrence of any character in the string delim or the terminating 0 character and replaces it with a 10 The location of the next character after t
185. ome library functions might also use dynamic memory notably those from the Standard IO facili ties so make sure the changes will be done early enough in the startup sequence The variables __malloc_heap_start and __malloc_heap_end can be used to restrict the malloc function to a certain memory region These variables are stati cally initialized to point to__ heap_start and__ heap_end respectively where _ heap_start is filled in by the linker to point just beyond bss and__ heap_end is set to 0 which makes malloc assume the heap is below the stack If the heap is going to be moved to external RAM __malloc_heap_end must be adjusted accordingly This can either be done at run time by writing directly to this variable or it can be done automatically at link time by adjusting the value of the symbol __heap_end The following example shows a linker command to relocate the entire data and bss segments and the heap to location 0x1100 in external RAM The heap will extend up to address Oxffff avr gcc W1 Tdata 0x801100 defsym __heap_end 0x80ffff Note See explanation for offset 0x800000 See the chapter about using gcc for the w1 options 0x0100 on board RAM external RAM Ox10FF 0x1100 OxFFFF SP 1 _ _malloc_heap_end __ heap_end RAMEND brkval _ Malloc_heap_start __heap_start __bss_end _ data_en _ bss start data start Figure 3 Internal RAM stack only external RAM var
186. ommunicate with the circuitry connected to the controller The AVR series of microcontrollers offers two different paradigms to perform this task There s a separate IO address space available as it is known from some high level CISC CPUs that can be addressed with specific IO instructions that are applicable to some or all of the IO address space in out sbi etc The entire IO address space is also made available as memory mapped IO i e it can be accessed using all the MCU instructions that are applicable to normal data memory The IO register space is mapped into the data memory address space with an offset of 0x20 since the bottom of this space is reserved for direct access to the MCU registers Actual SRAM is available only behind the IO register area starting at either address 0x60 or 0x100 depending on the device AVR Libc supports both these paradigms While by default the implementation uses memory mapped IO access this is hidden from the programmer So the programmer can access IO registers either with a special function like outb include lt avr io h gt outb PORTA 0x33 or they can assign a value directly to the symbolic address PORTA 0x33 The compiler s choice of which method to use when actually accessing the IO port is completely independent of the way the programmer chooses to write the code So even if the programmer uses the memory mapped paradigm and writes PORTA 0x40 Generated on
187. on especially for the AVR version of the compiler it may take some time to figure out the implementation details by studying the compiler and assembler source code There are also a few sample programs available in the net Hopefully this document will help to increase their number It s assumed that you are familiar with writing AVR assembler programs because this is not an AVR assembler programming tutorial It s not a C language tutorial either Note that this document does not cover file written completely in assembler language refer to avr libc and assembler programs for this Copyright C 2001 2002 by egnite Software GmbH Permission is granted to copy and distribute verbatim copies of this manual provided that the copyright notice and this permission notice are preserved on all copies Permis sion is granted to copy and distribute modified versions of this manual provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one This document describes version 3 3 of the compiler There may be some parts which hadn t been completely understood by the author himself and not all samples had been tested so far Because the author is German and not familiar with the English language there are definitely some typos and syntax errors in the text As a programmer the author knows that a wrong documentation sometimes might be worse than none Any way he decided to offer his
188. or the get argument have been provided thus attempting to open a stream with no IO intent at all or that insufficient dynamic memory is available to establish a new stream Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 47 If the put function pointer is provided the stream is opened with write intent The function passed as put shall take one character to write to the device as argument and shall return 0 if the output was successful and a nonzero value if the character could not be sent to the device If the get function pointer is provided the stream is opened with read intent The function passed as get shall take no arguments and return one character from the device passed as an int type If an error occurs when trying to read from the device it shall return 1 If both functions are provided the stream is opened with read and write intent The first stream opened with read intent is assigned to st din and the first one opened with write intent is assigned to both stdout and stderr The third parameter opt s is currently unused but reserved for future extensions fdevopen uses calloc und thus malloc in order to allocate the storage for the new stream 5 17 3 4 int feof FILE x _ stream Test the end of file flag of st ream This flag can only be cleared by a call to clearerr Note Since there is currently no notion for end of file on a device this funct
189. ot fit into a single register the compiler will automatically assign enough registers to hold the entire operand In the assembler code you use A0 to refer to the lowest byte of the first operand A1 to the lowest byte of the second operand and so on The next byte of the first operand will be B0 the next byte SCO and so on This also implies that it is often neccessary to cast the type of an input operand to the desired size A final problem may arise while using pointer register pairs If you define an input operand e ptr and the compiler selects register Z 130 131 then SAO refers to r30 and B0 refers to r31 But both versions will fail during the assembly stage of the compiler if you explicitely need Z like in ld r24 Z If you write ld r24 a0 with a lower case a following the percent sign then the compiler will create the proper assembler line 7 4 4 Clobbers As stated previously the last part of the asm statement the list of clobbers may be omitted including the colon seperator However if you are using registers which had not been passed as operands you need to inform the compiler about this The following example will do an atomic increment It increments an 8 bit value pointed to by a pointer variable in one go without being interrupted by an interrupt routine or another thread in a multithreaded environment Note that we must use a pointer because the incremented value needs to be stored befo
190. ound it by combining a skip instruction together with a relative jump r jmp instruction which will need one additional word of ROM Another side effect of optimzation is that variable usage is restricted to the area of code where it is actually used So if a variable was placed in a register at the beginning of some function this same register can be re used later on if the compiler notices that the first variable is no longer used inside that function even though the variable is still in lexical scope When trying to examine the variable in avr gdb the displayed result will then look garbled So in order to avoid these side effects optimization can be turned off while debugging However some of these optimizations might also have the side effect of uncovering bugs that would otherwise not be obvious so it must be noted that turning off opti mization can easily change the bug pattern In most cases you are better off leaving optimizations enabled while debugging Back to FAQ Index 7 3 12 How do I trace an assembler file in avr gdb When using the g compiler option avr gcc only generates line number and other debug information for C and C files that pass the compiler Functions that don t have line number information will be completely skipped by a single step command in gdb This includes functions linked from a standard library but by default also functions defined in an assembler source file since the g compiler switch doe
191. ow to do this using few lines of assembler code or to the chapter about memory sections for an example written in C The explanation of malloc contains a discussion about the use of internal RAM vs external RAM in particular with respect to the various possible locations of the heap Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 132 area reserved for malloc It also explains the linker command line options that are required to move the memory regions away from their respective standard locations in internal RAM Finally if the application simply wants to use the additional RAM for private data storage kept outside the domain of the C compiler e g through a char variable initialized directly to a particular address it would be sufficient to defer the initializa tion of the external RAM interface to the beginning of main so no tweaking of the init section is necessary The same applies if only the heap is going to be located there since the application start up code does not affect the heap It is not recommended to locate the stack in external RAM In general accessing exter nal RAM is slower than internal RAM and errata of some AVR devices even prevent this configuration from working properly at all Back to FAQ Index 7 3 17 Which O flag to use There s a common misconception that larger numbers behind the O option might auto matically cause better opt
192. owever in particular for very short delays the overhead of setting up a hardware timer is too much compared to the overall delay time Two inline functions are provided for the actual delay algorithms Two wrapper functions allow the specification of microsecond and millisecond delays directly using the application supplied macro F_CPU as the CPU clock frequency in Hertz These functions operate on double typed arguments however when optimiza tion is turned on the entire floating point calculation will be done at compile time Functions e _ inline void _delay_loop_1 uint8_t __count e _ inline void _delay_loop_2 uint16_t __count e __inline__ void _delay_us double __us e _ imline_ void _delay_ms double __ms 5 3 2 Function Documentation 5 3 2 1 inline__ void _delay_loop_1 uint8_t__count static Delay loop using an 8 bit counter ___count so up to 256 iterations are possible The value 256 would have to be passed as 0 The loop executes three CPU cycles per iteration not including the overhead the compiler needs to setup the counter register Thus at a CPU speed of 1 MHz delays of up to 768 microseconds can be achieved 5 3 2 2 inline__ void _delay_loop_2 uint16_t __count static Delay loop using a 16 bit counter __count so up to 65536 iterations are possible The value 65536 would have to be passed as 0 The loop executes four CPU cycles per iteration not including the overhead the compi
193. plains CRC s in very clear and concise terms Well worth the effort to obtain a copy Functions e _ inline_ uintl6_t_crcl6_update uint16_t __crc uint8_t _ data e __inline__ uintl6_t __crc_xmodem_update uint16_t __crc uint8_t __ data e __inline__ uintl6_t _crce_ccitt_update uintl6_t__crc uint8_t__ data 5 2 2 Function Documentation 5 2 2 1 inline__ uint16_t _crc16_update uintl6_t _ crc uint8_t _ data static Optimized CRC 16 calcutation Polynomial x16 x15 x 2 1 0xa001 Initial value Oxffff This CRC is normally used in disk drive controllers 5 2 2 2 inline__ uint16_t _crc_ccitt_update uint16_t __crc uint8_t _ data static Optimized CRC CCITT calculation Polynomial x16 x12 x 5 1 0x8408 Initial value Oxffff This is the CRC used by PPP and IrDA See RFC1171 PPP protocol and IrDA IrLAP 1 1 Note Although the CCITT polynomial is the same as that used by the Xmodem protocol they are quite different The difference is in how the bits are shifted through the alorgithm Xmodem shifts the MSB of the CRC and the input first while CCITT shifts the LSB of the CRC and the input first The following is the equivalent functionality written in C Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 3 Busy wait delay loops 13 uint16_t crc_ccitt_update uintl6_t crc uint8_t data data 108 crc data data lt lt 4 return uint16_t data l
194. py_P char x PGM_P size_t size_t strnlen_P PGM_P size_t _ ATTR_CONST Define Documentation 5 7 2 1 define PGM_P const prog_char x Used to declare a variable that is a pointer to a string in program space 5 7 2 2 define pgm_read_byte address_short pgm_read_byte_near address_ short Read a byte from the program space with a 16 bit near address Note The address is a byte address The address is in the program space Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 7 Program Space String Utilities 21 5 7 2 3 define pgm_read_byte_far address_long _ ELPM uint32_ t address_long Read a byte from the program space with a 32 bit far address Note The address is a byte address The address is in the program space 5 7 2 4 define pgm_read_byte_near address_short _ LPM uint16_ t address_short Read a byte from the program space with a 16 bit near address Note The address is a byte address The address is in the program space 5 7 2 5 define pgm_read_dword address_short pgm_read_dword_ near address_short Read a double word from the program space with a 16 bit near address Note The address is a byte address The address is in the program space 5 7 2 6 define pgm_read_dword_far address_long _ ELPM_dword uint32_ t address_long Read a double word from the program space with a 32 bit far address Note The address is a byte a
195. r Similar to fgets except that it will operate on stream st din and the trailing newline if any will not be stored in the string It is the caller s responsibility to provide enough storage to hold the characters read 5 17 3 18 int printf const char __fmt The function printf performs formatted output to stream stderr See vfprintf for details 5 17 3 19 int printf_P const char x __fmt Variant of printf that uses a fmt string that resides in program memory 5 17 3 20 int puts const char x __str Write the string pointed to by st r and a trailing newline character to stdout 5 17 3 21 int puts_P const char __str Variant of puts where st r resides in program memory 5 17 3 22 int scanf const char __fmt The function scanf performs formatted input from stream st din See vfscanf for details 5 17 3 23 int scanf_P const char __fmt Variant of scanf where fmt resides in program memory 5 17 3 24 int snprintf char x __s size_t __n const char x __fmt Like sprintf but instead of assuming s to be of infinite size no more than n characters including the trailing NUL character will be converted to s Returns the number of characters that would have been written to s if there were enough space Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 50 5 17 3 25 int snprintf_P char x __s size_t __n const cha
196. r __fint Variant of snprint f that uses a fmt string that resides in program memory 5 17 3 26 int sprintf char __s const char __fmt Variant of printf that sends the formatted characters to string s 5 17 3 27 int sprintf_P char x __s const char x __fmt Variant of sprintf that uses a fmt string that resides in program memory 5 17 3 28 int sscanf const char x __buf const char x __fmt The function sscanf performs formatted input reading the input data from the buffer pointed to by buf See vfscanf for details 5 17 3 29 int sscanf_P const char x __buf const char x __fmt Variant of sscanf using a fmt string in program memory 5 17 3 30 int ungetc int __c FILE x __stream The ungetc function pushes the character c converted to an unsigned char back onto the input stream pointed to by stream The pushed back character will be returned by a subsequent read on the stream Currently only a single character can be pushed back onto the stream The ungetc function returns the character pushed back after the conversion or EOF if the operation fails If the value of the argument c character equals EOF the operation will fail and the stream will remain unchanged 5 17 3 31 int vfprintf FILE x _ stream const char __fimt va_list __ap vfprintf is the central facility of the print f family of functions It outputs values to stream under control of a format str
197. r each write operation Note 16 24Cxx devices can become write protected by strapping their WC pin to logic high Leaving it unconnected is explicitly allowed and constitutes logic low level i e no write protection In case of a write protected device all data transfer attempts will be NACKed by the device Note that some devices might not implement this Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 6 avr libc Data Structure Documentation 110 6 avr libc Data Structure Documentation 6 1 div_t Struct Reference 6 1 1 Detailed Description Result type for function div Data Fields int quot intrem 6 1 2 Field Documentation 6 1 2 1 int div_t quot The Quotient 6 1 2 2 int div_t rem The Remainder The documentation for this struct was generated from the following file stdlib h 6 2 Idiv_t Struct Reference 6 2 1 Detailed Description Result type for function Idiv Data Fields long quot long rem 6 2 2 Field Documentation 6 2 2 1 long Idiv_t quot The Quotient Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 avr libc Page Documentation 111 6 2 2 2 long Idiv_t rem The Remainder The documentation for this struct was generated from the following file stdlib h 7 avr libc Page Documentation 7 1 Acknowledgments This document tries to tie together the labors of a large group of people Without these individuals e
198. re interrupts are enabled Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 146 asm volatile moli ld r24 a0 ine 124 st a0 r24 sel ar ptr r24 n t n t n t n t n t The compiler might produce the following code eli ld r24 Z inc r24 st Z r24 sei One easy solution to avoid clobbering register r24 is to make use of the special tem porary register __tmp_reg__ defined by the compiler asm volatile cli ld _tmp_reg__ a0 inc __tmp_reg__ st a0 __tmp_reg__ sel e ptr n t n t n t n t n t The compiler is prepared to reload this register next time it uses it Another problem with the above code is that it should not be called in code sections where interrupts are disabled and should be kept disabled because it will enable interrupts at the end We may store the current status but then we need another register Again we can solve this without clobbering a fixed but let the compiler select it This could be done with the help of a local C variable uint8_t s asm volatile in 0 __SREG__ cli ld __tmp_reg__ o st Sal _ tmp_ out _ SREG__ amp r s an e ptr al inc __tmp_reg__ Teg 0 TANGA mne what Name ANNE ANNE Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 147 Now
199. re the length of src is less than that of n the remainder of dest will be padded with nulls Returns The strncpy_P function returns a pointer to the destination string dest 5 7 3 13 size_t strnlen_P PGM_P src size_t len Determine the length of a fixed size string The strnlen_P function is similar to strnlen except that src is a pointer to a string in program space Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 8 Additional notes from lt avr sfr_defs h gt 26 Returns The strnlen_P function returns strlen_P src if that is less than len or len if there is no 0 character among the first len characters pointed to by src 5 8 Additional notes from lt avr sfr_defs h gt The lt avr sfr_defs h gt file is included by all of the lt avr ioXXXX h gt files which use macros defined here to make the special function register definitions look like C variables or simple constants depending on the _SFR_ASM_COMPAT define Some examples from lt avr iom128 h gt to show how to define such macros define PORTA _SFR_108 0x1b define TCNT1 _SFR_I016 0x2c define PORTF _SFR_MEM8 0x61 define TCNT3 _SFR_MEM16 0x88 If _SFR_ASM_COMPAT is not defined C programs can use names like PORTA directly in C expressions also on the left side of assignment operators and GCC will do the right thing use short I O instructions if possible The __SFR_OFFSET definition is not used in any way in this case
200. rgin char x __malloc_heap_start e char x _ malloc_heap_end size_t__malloc_margin 32 size_t __malloc_margin char __malloc_heap_start amp __heap_start e char x __malloc_heap_start char __malloc_heap_end amp __heap_end e char x __malloc_heap_end 5 18 2 Define Documentation 5 18 2 1 define DTOSTR_ALWAYS_SIGN 0x01 x put or for positives Bit value that can be passed in flags to dtostre 5 18 2 2 define DTOSTR_PLUS_SIGN 0x02 x put rather than x Bit value that can be passed in flags to dtostre 5 18 2 3 define DTOSTR_UPPERCASE 0x04 put E rather e x Bit value that can be passed in flags to dtostre 5 18 2 4 define RAND_MAX 0x7FFF Highest number that can be generated by rand Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 59 5 18 2 5 define RANDOM_MAX 0x7FFFFFFF Highest number that can be generated by random 5 18 3 Typedef Documentation 5 18 3 1 typedef int __compar_fn_t const void const void x Comparision function type for qsort just for convenience 5 18 4 Function Documentation 5 18 4 1 _ inline void abort void The abort function causes abnormal program termination to occur In the limited AVR environment execution is effectively halted by entering an infinite loop 5 18 4 2 int abs int _ 1 The abs function computes the absolute value of the integer i Note The
201. rintf avr_stdio 49 vfprintf_P Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen INDEX 190 avr_stdio 52 vfscanf avr_stdio 52 vfscanf_P avr_stdio 54 vsnprintf avr_stdio 55 vsnprintf_P avr_stdio 55 vsprintf avr_stdio 55 vsprintf_P avr_stdio 55 Watchdog timer handling 27 wdt_disable avr_watchdog 27 wdt_enable avr_watchdog 28 wdt_reset avr_watchdog 28 WDTO_120MS avr_watchdog 28 WDTO_15MS avr_watchdog 28 WDTO_1S avr_watchdog 28 WDTO_250MS avr_watchdog 28 WDTO_2S avr_watchdog 28 WDTO_30MS avr_watchdog 29 WDTO_500MS avr_watchdog 29 WDTO_60MS avr_watchdog 29 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen
202. rn 1 error not in start condition NB do not send stop condition send SLA W TWDR sla TW_WRITE TWCR _BV TWINT _BV TWEN clear interrupt to start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWI 104 case TW_MT_SLA_ACK break case TW_MT_SLA_NACK goto restart case TW_MT_ARB_LOST goto begin default goto error TWDR eeaddr TWCR _BV TWINT _BV TWEN while TWCR amp _BV TWINT switch twst TW_STATUS case TW_MT_DATA_ACK break case TW_MT_DATA_NACK goto quit case TW_MT_ARB_LOST goto begin default goto error for len gt 0 len TWDR buf TWCR _BV TWINT _BV TW while TWCR amp _BV TWINT switch twst TW_STATUS case TW_MT_DATA_NACK goto error case TW_MT_DATA_ACK rv break default goto error quit TWCR _BV TWINT _BV TWSTO return rv error rv 1 goto quit EN nack during select device busy writing re arbitrate must send stop condition low 8 bits of addr clear interrupt to start transmission 0 wait for transmission must send stop condition start transmission 0 wait for transmission device write protected
203. ror not in start condition NB do not send stop condition Note 10 send SLA W Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWI 101 TWDR sla TW_WRITE TWCR _BV TWINT _BV TWEN while TWCR amp _BV TWINT switch twst TW_STATUS case TW_MT_SLA_ACK break case TW_MT_SLA_NACK goto restart case TW_MT_ARB_LOST goto begin default goto error TWDR eeaddr TWCR _BV TWINT _BV TWEN while TWCR amp _BV TWINT switch twst TW_STATUS case TW_MT_DATA_ACK break case TW_MT_DATA_NACK goto quit case TW_MT_ARB_LOST goto begin default goto error Note 12 Next cycle s TWCR _BV TWINT _BV TWSTA while TWCR _BV TWINT switch twst TW_STATUS case TW_START case TW_REP_START break case TW_MT_ARB_LOST goto begin default goto error send SLA R clear interrupt to start transmission 0 wait for transmission nack during select device busy writing Note 11 re arbitrate must send stop condition low 8 bits of addr clear interrupt to start transmission 0 wait for transmission must send stop condition master receiver mode _BV TWEN 0 send rep start condition wait for transmission OK but should no
204. rupt ART 1 Receive Complete Interrupt ART 1 Transmit Complete Interrupt ART Data Register Empty Interrupt ART Receive Complete Interrupt ART Transmit Complete Interrupt SART 0 Data Register Empty Interrupt SART 0 Receive Complete Interrupt SART 0 Transmit Complete Interrupt SART 1 Data Register Empty Interrupt SART 1 Receive Complete Interrupt SART 1 Transmit Complete Interrupt clcicicicicicicicicicica Global manipulation of the interrupt flag The global interrupt flag is maintained in the I bit of the status register SREG e define sei __asm volatile sei define cli __asm volatile__ cli Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 20 Interrupts and Signals 79 Allowing specific system wide interrupts In addition to globally enabling interrupts each device s particular interrupt needs to be enabled separately if interrupts for this device are desired While some devices maintain their interrupt enable bit inside the device s register set external and timer interrupts have system wide configuration registers Example Enable timer 1 overflow interrupts timer_enable_int _BV TOIE1 Do some work Disable all timer interrupts timer_enable_int 0 Note Be careful when you use these functions If you already have a different interrupt enabled you could inadvertantly disable it by enabling anot
205. s The memmove function returns a pointer to dest 5 19 2 6 void x memset void dest int val size_t len Fill memory with a constant byte The memset function fills the first len bytes of the memory area pointed to by dest with the constant byte val Returns The memset function returns a pointer to the memory area dest Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 19 Strings 71 5 19 2 7 int strcasecmp const char x s1 const char s2 Compare two strings ignoring case The strcasecmp function compares the two strings s1 and s2 ignoring the case of the characters Returns The strcasecmp function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 5 19 2 8 char x strcat char x dest const char x src Concatenate two strings The strcat function appends the src string to the dest string overwriting the 0 char acter at the end of dest and then adds a terminating 0 character The strings may not overlap and the dest string must have enough space for the result Returns The strcat function returns a pointer to the resulting string dest 5 19 2 9 char x strchr const char x src int val Locate character in string The strchr function returns a pointer to the first occurrence of the character val in the string src Here character means byte these functions do not work
206. s not apply to the assembler Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 125 So in order to debug an assembler input file possibly one that has to be passed through the C preprocessor it s the assembler that needs to be told to include line number information into the output file Other debug information like data types and variable allocation cannot be generated since unlike a compiler the assembler basically doesn t know about this This is done using the GNU assembler option gstabs Example avr as mmcu atmegal28 gstabs o foo o foo s When the assembler is not called directly but through the C compiler frontend either implicitly by passing a source file ending in S or explicitly using x assembler with cpp the compiler frontend needs to be told to pass the gstabs option down to the assembler This is done using Wa gstabs Please take care to only pass this option when compiling an assembler input file Otherwise the assembler code that results from the C compilation stage will also get line number information which confuses the debugger Note You can also use Wa gstabs since the compiler will add the extra for you Example EXTRA_OPTS Wall mmcu atmegal28 x assembler with cpp avr gcc Wa gstabs EXTRA_OPTS c o foo o foo S Also note that the debugger might get confused when entering a piece of code that has a non local lab
207. sage 136 7 3 25 Why are many interrupt flags cleared by writing a logical 1 137 7 3 26 Why have programmed fuses the bit value 0 137 7 3 27 Which AVR specific assembler operators are available 138 TA Tine AS m eee 138 741 GCC asm Sialement soe co ka ee tete Re eS 139 ioe Assembler Code s kn ce ee rar A Re 140 143 Inputand Output Operands 2 20 5 525 284 4 8 141 SAA COBOS 2 s e RR ES a a Ee 145 245 Assembler Macros 54 5555 SAG RES EES 147 TAG Stub PUNENONS es so egr aeei e eee ES 148 7 4 7 C Names Used in AssemblerCode 149 TAR LINKS ocene eee he ee ee a 150 Ao Usima MANG IJ lt ec nk eane i we ae WEES re RASS 150 ANE a ma eee 150 7 5 2 Internal vs external RAM 151 7 5 3 Tunables for malloc 152 254 Implementation details pc o o s corpua oranga 153 7 6 Release Numbering and Methodology 155 7 6 1 Release Version Numbering Scheme 155 dbz Releasing AVR LIBE gt lt lt 6 0 ordre 155 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 1 AVR Libc 1 7 1 Memory Sections 400 80 o o a eh ee Epa 158 rs ki foo I e 158 Tee Theta Sociis ce ed e e 159 Tela The DESDECUON ok a RARA ROSS 159 TIA The ESPTOM Section lt lt e aa cocaina 54 was 159 Tha LOS MOU Secon lt q GS a a o i Se N 159 fx Mil MLB i e e 160 TAF The MniN Sections os c cesset tepee ees 161 7
208. savannah gnu org projects simulavr Installation AVaRice http avarice sourceforge net Installation 7 8 3 GNU Binutils for the AVR target The binutils package provides all the low level utilities needed in building and ma nipulating object files Once installed your environment will have an AVR assembler avr as linker avr 1ad and librarian avr ar and avr ranlib In addi tion you get tools which extract data from object files avr objcopy dissassem ble object file information avr objdump and strip information from object files avr strip Before we can build the C compiler these tools need to be in place Download and unpack the source files bunzip2 c binutils lt version gt tar bz2 tar xf cd binutils lt version gt Note Replace with the version of the package you downloaded Note If you obtained a gzip compressed file gz use gunzip instead of bunzip2 It is usually a good idea to configure and build binutils in a subdirectory so as not to pollute the source with the compiled files This is recommended by the binutils developers mkdir obj avr cd obj avr The next step is to configure and build the tools This is done by supplying arguments to the configure script that enable the AVR specific options configure prefix PREFIX target avr disable nls Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 8 Installing the GNU Tool Chain 166 If you
209. se C on the AVR Shouldn t I initialize all my variables Why do some 16 bit timer registers sometimes get trashed How do I use a define d constant in an asm statement Why does the PC randomly jump around when single stepping through my pro gram in avr gdb How do I trace an assembler file in avr gdb How do I pass an IO port as a parameter to a function What registers are used by the C compiler How do I put an array of strings completely in ROM How to use external RAM Which O flag to use How do I relocate code to a fixed address My UART is generating nonsense My ATmega128 keeps crashing Port F is completely broken Why do all my foo bar strings eat up the SRAM Why does the compiler compile an 8 bit operation that uses bitwise operators into a 16 bit operation in assembly How to detect RAM memory and variable overlap problems Is it really impossible to program the ATtinyXX in C What is this clock skew detected messsage Why are many interrupt flags cleared by writing a logical 1 Why have programmed fuses the bit value 0 Which AVR specific assembler operators are available Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 119 7 3 2 My program doesn t recognize a variable updated within an interrupt rou tine When using the optimizer in a loop like the following one uint8_t flag while flag 0 the compiler
210. sing the following options in the link stage W1 u vfscanf lscanf_min lm In addition to the restrictions of the standard version this version implements no field width specification no conversion assignment suppression flag x no n specification and no general format character matching at all All characters in fmt that do not comprise a conversion specification will simply be ignored including white space that is normally used to consume any amount of white space in the input stream However the usual skip of initial white space in the formats that support it is implemented Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 56 5 17 3 34 int vfscanf_P FILE x __ stream const char x __ fmt va_list __ap Variant of vfscanf using a fmt string in program memory 5 17 3 35 int vsnprintf char _s size_t__n const char __fmt va_list ap Like vsprintf but instead of assuming s to be of infinite size no more than n characters including the trailing NUL character will be converted to s Returns the number of characters that would have been written to s if there were enough space 5 17 3 36 int vsnprintf_P char x __s size_t __n const char x _ fmt va_list ap Variant of vsnprintf that uses a fmt string that resides in program memory 5 17 3 37 int vsprintf char x __s const char x __ fmt va_list ap Like sprintf but takes a variable argument list for the argum
211. sscanf const char __buf const char x__fmt int sscanf_P const char x __ buf const char __fmt FILE fdevopen int put char int get void int opts _ attribute_ unused 5 17 2 Define Documentation 5 17 2 1 define EOF 1 EOF declares the value that is returned by various standard IO functions in case of an error Since the AVR platform currently doesn t contain an abstraction for actual files its origin as end of file is somewhat meaningless here 5 17 2 2 define FILE struct _ file FILE is the opaque structure that is passed around between the various standard IO functions 5 17 2 3 Hdefine getc __stream fgetc __stream The macro get c used to be a fast macro implementation with a functionality iden tical to fgetc For space constraints in avr libc it is just an alias for fgetc 5 17 2 4 define getchar void fgetc stdin The macro get char reads a character from stdin Return values and error handling is identical to fgetc 5 17 2 5 define putc __c _ stream fputc __c __ stream The macro putc used to be a fast macro implementation with a functionality iden tical to fputc For space constraints in avr libc it is just an alias for fputc 5 17 2 6 define putchar __c fputc __c stdout The macro put char sends character c to stdout Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 17 Standard IO facilities 46 5 17 2 7 define stderr
212. ssembler Code for more details Back to FAQ Index Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 120 7 3 5 How to modify MCUCR or WDTCR early The method of early initialization MCUCR WDTCR or anything else is different and more flexible in the current version Basically write a small assembler file which looks like this begin xram S include lt avr io h gt section init1 ax progbits idi r16 _BV SRE _BV SRW out _SFR_IO_ADDR MCUCR r16 end xram S Assemble it link the resulting xram o with other files in your program and this piece of code will be inserted in initialization code which is run right after reset See the linker script for comments about the new initN sections which one to use etc The advantage of this method is that you can insert any initialization code you want just remember that this is very early startup no stack and no __zero_reg__ yet and no program memory space is wasted if this feature is not used There should be no need to modify linker scripts anymore except for some very spe cial cases It is best to leave __stack at its default value end of internal SRAM faster and required on some devices like ATmegal61 because of errata and add W1 Tdata 0x801100 to start the data section above the stack For more information on using sections including how to use them from C code see Memory Sections
213. t lt 8 hi8 crc uint8_t data gt gt 4 uint16_t data lt lt 3 5 2 2 3 inline__ uint16_t _crc_xmodem_update uint16_t __crc uint8_t _ data static Optimized CRC XMODEM calculation Polynomial x 16 x 12 x 5 1 0x1021 Initial value 0x0 This is the CRC used by the Xmodem CRC protocol The following is the equivalent functionality written in C uint16_t crc_xmodem_update uint16_t crc uint8_t data int i cre cre uint16_t data lt lt 8 for i 0 i lt 8 i if cre amp 0x8000 ere cre lt lt 1 0x1021 else cre lt lt 1 return crc 5 3 Busy wait delay loops 5 3 1 Detailed Description define F_CPU 1000000UL 1 MHz define F_CPU 14 7456E6 include lt avr delay h gt The functions in this header file implement simple delay loops that perform a busy waiting They are typically used to facilitate short delays in the program execution They are implemented as count down loops with a well known CPU cycle count per Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 3 Busy wait delay loops 14 loop iteration As such no other processing can occur simultaneously It should be kept in mind that the functions described here do not disable interrupts In general for long delays the use of hardware timers is much preferrable as they free the CPU and allow for concurrent processing of other events while the timer is running H
214. t where program instructions are stored starts at location 0x0 fin12 gt Emol fini0 0x000000cc _etext data 0x00800060 0x0 load address 0x000000cc 0x00800060 PROVIDE __data_start data gnu linkonce d 0x00800060 ALIGN 0x2 0x00800060 _edata 0x00800060 PROVIDE __data_end bss 0x00800060 0x3 0x00800060 PROVIDE __bss_start bss COMMON COMMON 0x00800060 0x3 demo o 0x0 size before relaxing 0x00800060 direction Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 23 A simple project 93 0x00800061 pwm 0x00800063 PROVIDE __bss_end 0x000000cc _ data_load_start LOADADDR data 0x000000cc data_load_end __data_load_start SIZEOF noinit 0x00800063 0x0 0x00800063 PROVIDE __noinit_start noinit 0x00800063 PROVIDE __noinit_end 0x00800063 _end 0x00800063 PROVIDE __heap_start eeprom 0x00810000 0x0 load address 0x000000cc eeprom 0x00810000 __eeprom_end The last address in the text segment is location 0x 2 denoted by _etext so the instructions use up 242 bytes of FLASH The data segment where initialized static variables are stored starts at location 0x60 which is the first address after the register bank on a 2313 processor The next available address in the data segment is also location 0x 60 so the application has no initialized data The bss segment where uninitialized data is stored starts
215. t any of the APIs have changed The only changes that should be made to a stable branch are bug fixes and under some circumstances additional functionality e g adding support for a new device If major version number has changed this implies that the required versions of gcc and binutils have changed Consult the README file in the toplevel directory of the AVR Libc source for which versions are required 7 6 1 2 Development Versions The major version number of a development series is always the same as the last stable release The minor version number of a development series is always an odd number and is 1 more than the last stable release The patch version number of a development series is always 0 until a new branch is cut at which point the patch number is changed to 90 to denote the branch is approaching a release and the date appended to the version to denote that it is still in development All versions in development in cvs will also always have the date appended as a fourth version number The format of the date will be YY Y YMMDD So the development version number will look like this 1 1 0 20030825 While a pre release version number on a branch destined to become either 1 2 or 2 0 will look like this 1 1 90 20030828 7 6 2 Releasing AVR Libc The information in this section is only relevant to AVR Libc developers and can be ignored by end users Note In what follows I assume you know how to use cvs and how
216. t char bar PROGMEM Bar PGM_P array 2 PROGMEM foo bar int main void char buf 32 PGM_P p int i memcpy_P amp p amp arraylil sizeof PGM_P strcpy_P buf p return 0 Looking at the disassembly of the resulting object file we see that array is in flash as such 00000026 lt array gt 267 2e 00 28 2a 00 0x002e 0x002a word word 0000002a lt bar gt 2a 42 61 72 00 0000002e lt foo gt 2e 46 6f 6f 00 foo is at addr 0x002e bar is at addr 0x002a array is at addr 0x0026 Then in main we see this ogee enone aki Bar Foo memcpy_P 8p amp arraylil sizeof PGM_P 70 66 Of add E22 r22 12 TT LE adc 423 r23 74 6a 5d subi r22 OxDA 76 7f 4f sbci r23 OxFF 78 42 eo ldi 20 0x2 Ta 50 e0 idi r21 0x00 218 255 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 3 Frequently Asked Questions 131 Te ce 01 movw r24 r28 Te 81 96 adiw r24 0x21 33 80 08 do rcall 16 0X92 This code reads the pointer to the desired string from the ROM table array into a register pair The value of i in r22 r23 is doubled to accomodate for the word offset required to access array then the address of array 0x26 is added by subtracting the negated address Oxffda The address of variable p is computed by adding its offset within the stack frame 33 to the Y pointer register and memcpy_P is called strcpy_P buf p 82 69 a
217. t defaults to 1 The following conversion flags are supported e Matches a literal character This is not a conversion e d Matches an optionally signed decimal integer the next pointer must be a pointer to int i Matches an optionally signed integer the next pointer must be a pointer to int The integer is read in base 16 if it begins with Ox or OX in base 8 if it begins with 0 and in base 10 otherwise Only characters that correspond to the base are used o Matches an octal integer the next pointer must be a pointer to unsigned int u Matches an optionally signed decimal integer the next pointer must be a pointer to unsigned int x Matches an optionally signed hexadecimal integer the next pointer must be a pointer to unsigned int e f Matches an optionally signed floating point number the next pointer must be a pointer to float e e g E G Equivalent to f s Matches a sequence of non white space characters the next pointer must be a pointer to char and the array must be large enough to accept all the sequence and the terminating NUL character The input string stops at white space or at the maximum field width whichever occurs first e c Matches a sequence of width count characters default 1 the next pointer must be a pointer to char and there must be enough room for all the characters no terminating NUL is added The usual skip of leading white space is suppressed To skip white space first use
218. t happen Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TWD 102 TWDR TWCR while TWCR amp _BV TWINT switch twst TW_STATUS case TW_MR_SLA_ACK break sla TW_READ 0 wait for transmission case TW_MR_SLA_NACK goto quit case TW_MR_ARB_LOST goto begin default goto error for twcr _BV TWINT _BV TWEN _BV TWEA Note 13 len gt 0 len if len 1 twcr _BV TWINT _BV TWEN send NAK this time TWCR twcr clear int to start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MR_DATA_NACK len 0 force end of loop FALLTHROUGH case TW_MR_DATA_ACK buf TWDR rv break default goto error quit Note 14 TWCR _BV TWINT _BV TWSTO _BV TWEN send stop condition return rv error rv 1 goto quit Write len bytes into EEPROM starting at eeaddr from buf This is a bit simpler than the previous function since both the address and the data bytes will be transfered in master transmitter mode thus no reselection of the device is necessary However the BE aR E a _BV TWINT _BV TWEN clear interrupt to start transmission Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 24 Example using the two wire interface TW
219. tarball to savannah Generate the latest documentation and upload to savannah Announce the release The following hypothetical diagram should help clarify version and branch relation ships Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 7 Memory Sections 158 HEAD 1 0 Branch 1 2 Branch cvs tag avr libc 1_0 branchpoint set version to 1 1 0 lt date gt cvs tag b avr libc 1_0 branch set version to 0 90 90 lt date gt Y set version to 1 0 cvs tag avr libc 1_0 release set version to 1 0 0 lt date gt 1 i set version to 1 0 1 cvs tag avr libc 1_0_1 release 1 cvs tag avr libc 1_2 branchpoint set version to 1 3 0 lt date gt MENJA RIDE ENE set version to 1 1 90 lt date gt i set version to 1 2 cvs tag avr libc 1_2 release t cvs tag avr libc 2 0 branchpoint set version to 2 1 0 lt date gt t Figure 5 Release tree 7 7 Memory Sections Remarks Need to list all the sections which are available to the avr Weak Bindings FIXME need to discuss the weak directive The following describes the various sections available 7 7 1 The text Section The text section contains the actual machine instructions which make up your program This section is further subdivided by the initN and finiN sections dicussed below Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 7 Memory Sections 159 Note The
220. ter in endptr If there were no digits at all however strtol stores the original value of nptr in endptr Thus if xnptr is not 0 but xxendptr is 0 on return the entire string was valid The strtol function returns the result of the conversion unless the value would under flow or overflow If no conversion could be performed 0 is returned If an overflow or underflow occurs errno is set to ERANGE and the function return value is clamped to LONG_MIN or LONG_MAX respectively Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 66 5 18 4 28 unsigned long strtoul const char x __nptr char xx __endptr int _ base The strtoul function converts the string in npt r to an unsigned long value The con version is done according to the given base which must be between 2 and 36 inclusive or be the special value 0 The string may begin with an arbitrary amount of white space as determined by iss pace followed by a single optional or sign If base is zero or 16 the string may then include a 0x prefix and the number will be read in base 16 otherwise a zero base is taken as 10 decimal unless the next character is 0 in which case it is taken as 8 octal The remainder of the string is converted to an unsigned long value in the obvious manner stopping at the first character which is not a valid digit in the given base In bases above 10 th
221. ter return from main or a call to exit These all are subparts of the text section The finiN sections are executed in descending order from 9 to 0 finit9 Unused User definable This is effectively where _exit starts fini8 Unused User definable fini7 Unused User definable Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 7 Memory Sections 162 fini6 Unused for C programs but used for destructors in C programs fini5 Unused User definable fini4 Unused User definable fini3 Unused User definable fini2 Unused User definable finil Unused User definable fini0 Goes into an infinite loop after program termination and completion of any _exit code execution of code in the fini9 gt finil sections 7 7 8 Using Sections in Assembler Code Example include lt avr io h gt section initl ax fprogbits Tai r0 Oxff out _SFR_IO_ADDR PORTB r0 out _SFR_IO_ADDR DDRB ro Note The ax progbits tells the assembler that the section is allocatable a executable x and contains data progbits For more detailed information on the section directive see the gas user manual 7 7 9 Using Sections in C Code Example include lt avr io h gt void my_init_portb void __attribute__ naked __attribute__ section init1 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 8 Installing the GNU Tool
222. the 0 flag is ignored A negative field width flag the converted value is to be left adjusted on the field boundary The converted value is padded on the right with blanks rather than on the left with blanks or zeros A overrides a 0 if both are given space A blank should be left before a positive number produced by a signed conversion d or i A sign must always be placed before a number produced by a signed conversion A overrides a space if both are used An optional decimal digit string specifying a minimum field width If the con verted value has fewer characters than the field width it will be padded with spaces on the left or right if the left adjust173 ment flag has been given to fill out the field width An optional precision in the form of a period followed by an optional digit string If the digit string is omitted the precision is taken as zero This gives the minimum number of digits to appear for d i 0 u x and X conversions or the maximum number of characters to be printed from a string for s conversions An optional 1 length modifier that specifies that the argument for the d i 0 u X or X conversion isa long int rather than int A character that specifies the type of conversion to be applied The conversion specifiers and their meanings are e diouxX The int or appropriate variant argument is converted to signed decimal d and i unsigned octal 0 unsigned
223. tine is expected to have two arguments which point to the key object and to an array member in that order and should return an integer less than equal to or greater than zero if the key object is found respectively to be less than to match or be greater than the array member The bsearch function returns a pointer to a matching member of the array or a null pointer if no match is found If two members compare as equal which member is matched is unspecified 5 18 4 7 void calloc size_t __nele size_t __ size Allocate nele elements of size each Identical to calling malloc using nele x size as argument except the allocated memory will be cleared to zero 5 18 4 8 div_t div int __num int __denom The div function computes the value num denom and returns the quotient and re mainder in a structure named div_t that contains two int members named quot and rem 5 18 4 9 char dtostre double __val char x __s unsigned char __prec unsigned char __flags The dtostre function converts the double value passed in val into an ASCII repre sentation that will be stored under s The caller is responsible for providing sufficient storage in s Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 18 General utilities 61 Conversion is done in the format d ddde177dd where there is one digit be fore the decimal point character and the number of digits after it is equal to the preci sion prec if the pre
224. tjmp and Longjmp 38 Standard Integer Types 40 Standard IO facilities 42 General utilities 56 Strings 68 Interrupts and Signals 76 Special function registers 81 Additional notes from lt avr sfr_defs h gt 26 Demo projects 83 A simple project 84 Example using the two wire interface TWD 96 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 3 avr libc Data Structure Index 6 3 avr libc Data Structure Index 3 1 avr libc Data Structures Here are the data structures with brief descriptions div_t 110 Idiv_t 110 4 avr libc Page Index 4 1 avr libc Related Pages Here is a list of all related documentation pages Acknowledgments 111 avr libc and assembler programs 112 Frequently Asked Questions 118 Inline Asm 138 Using malloc 150 Release Numbering and Methodology 155 Memory Sections 158 Installing the GNU Tool Chain 163 Using the avrdude program 169 Using the GNU tools 171 Todo List 180 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 5 avr libc Module Documentation 7 5 avr libc Module Documentation 5 1 Bootloader Support Utilities 5 1 1 Detailed Description include lt avr io h gt include lt avr boot h gt The macros in this module provide a C language interface to the bootloader support functionality of certain AVR processors These macros are designed to work with all sizes of flash memory Note Not all AVR processors provide bootloader support See your processor datash
225. tt_update avr_crc 11 _crc_xmodem_update avr_crc 12 _delay_loop_1 avr_delay 13 _delay_loop_2 avr_delay 13 _delay_ms avr_delay 13 _delay_us avr_delay 14 A simple project 83 abort avr_stdlib 58 abs avr_stdlib 58 acos avr_math 34 Additional notes from lt avr sfr_ defs h gt 25 asin avr_math 34 atan avr_math 34 atan2 avr_math 34 atof avr_stdlib 58 atoi avr_stdlib 58 atol avr_stdlib 58 AVR device specific IO definitions 16 avr_boot boot_is_spm_interrupt 7 boot_lock_bits_set 8 boot_lock_bits_set_safe 8 boot_page_erase 8 boot_page_erase_safe 8 boot_page_fill 8 boot_page_fill_safe 9 boot_page_write 9 boot_page_write_safe 9 boot_rww_busy 9 boot_rww_enable 9 boot_rww_enable_safe 9 boot_spm_busy 10 boot_spm_busy_wait 10 boot_spm_interrupt_disable 10 boot_spm_interrupt_enable 10 BOOTLOADER_SECTION 10 avr_crc _crc16_update 11 _crc_ccitt_update 11 _crc_xmodem_update 12 avr_delay _delay_loop_1 13 _delay_loop_2 13 _delay_ms 13 _delay_us 14 avr_eeprom _EEGET 15 _EEPUT 15 eeprom_busy_wait 15 INDEX 182 eeprom_is_ready 15 eeprom_read_block 16 eeprom_read_byte 16 eeprom_read_word 16 eeprom_write_block 16 eeprom_write_byte 16 eeprom_write_word 16 avr_errno EDOM 32 ERANGE 32 avr_interrupts cli 78 EMPTY_INTERRUPT 78 enable_external_int 79 INTERRUPT 79 sei 79 SIGNAL 79 timer_enable_int 80 avr_math acos 34 asin 34
226. uction By default a jump to location 0 would be implied instead 7 2 4 Pseudo ops and operators The available pseudo ops in the assembler are described in the GNU assembler gas manual The manual can be found online as part of the current binutils release under http sources redhat com binutils As gas comes from a Unix origin its pseudo op and overall assembler syntax is slightly different than the one being used by other assemblers Numeric constants follow the C notation prefix Ox for hexadecimal constants expressions use a C like syntax Some common pseudo ops include Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 2 avr libc and assembler programs 117 e byte allocates single byte constants e ascii allocates a non terminated string of characters e asciz allocates a 0 terminated string of characters C string e data switches to the data section initialized RAM variables text switches to the text section code and ROM constants e set declares a symbol as a constant expression identical to equ e global or globl declares a public symbol that is visible to the linker e g function entry point global variable e extern declares a symbol to be externally defined this is effectively a comment only as gas treats all undefined symbols it encounters as globally undefined any way Note that org is available in gas as well but is a fairly pointless pseudo op in an as
227. value of npt r is stored in the location referenced by endpt r If the correct value would cause overflow plus or minus HUGE_VAL is returned ac cording to the sign of the value and ERANGE is stored in errno If the correct value would cause underflow zero is returned and ERANGE is stored in errno FIXME HUGE_VAL needs to be defined somewhere The bit pattern is Ox7fffffff but what number would this be 5 18 4 27 long strtol const char x __nptr char xx __endptr int __base The strtol function converts the string in nptr to a long value The conversion is done according to the given base which must be between 2 and 36 inclusive or be the special value 0 The string may begin with an arbitrary amount of white space as determined by iss pace followed by a single optional or sign If base is zero or 16 the string may then include a 0x prefix and the number will be read in base 16 otherwise a zero base is taken as 10 decimal unless the next character is 0 in which case it is taken as 8 octal The remainder of the string is converted to a long value in the obvious manner stopping at the first character which is not a valid digit in the given base In bases above 10 the letter A in either upper or lower case represents 10 B represents 11 and so forth with Z representing 35 If endptr is not NULL strtol stores the address of the first invalid charac
228. volatile in 0 1 mne out 1 32 Ant amp r input I _SFR_IO_ADDR port r output In this example an input value is read from a port and then an output value is written to the same port If the compiler would have choosen the same register for input and out put then the output value would have been destroyed on the first assembler instruction Fortunately this example uses the amp constraint modifier to instruct the compiler not to select any register for the output value which is used for any of the input operands Back to swapping Here is the code to swap high and low byte of a 16 bit value asm volatile mov tmp_reg__ A0 n t mov A0 BO Ane mov B0 __tmp_reg__ Ant r value 0 value First you will notice the usage of register __tmp_reg__ which we listed among other special registers in the Assembler Code section You can use this register without saving its contents Completely new are those letters A and B in A0 and B0 In fact they refer to two different 8 bit registers both containing a part of value Another example to swap bytes of a 32 bit value asm volatile mov _ tmp_reg__ A0 n t mov A0 D0 n t mov D0 _ tmp_reg__ n t mov __tmp_reg__ BO n t Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 4 Inline Asm 145 mov B0 CO inje mov C0 _ tmp_reg__ n t r value 0 value If operands do n
229. where these instructions could not be properly skipped e mno wrap For RIMP RCALL instructions don t allow the target address to wrap around for de vices that have more than 8 KB of memory e gstabs Generate stabs debugging symbols for assembler source lines This enables avr gdb to trace through assembler source files This option must not be used when assembling sources that have been generated by the C compiler these files already contain the appropriate line number information from the C source files e a cdhlmns file Turn on the assembler listing The sub options are e c omit false conditionals domit debugging directives e h include high level source 1 include assembly minclude macro expansions e n omit forms processing s include symbols file set the name of the listing file The various sub options can be combined into a single a option list file must be the last one in that case Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 10 Using the GNU tools 178 7 10 2 2 Examples for assembler options passed through the C compiler Re member that assembler options can be passed from the C compiler frontend using Wa see above so in order to include the C source code into the assembler listing in file foo 1st when compiling foo c the following compiler command line can be used avr gcc c 0 foo c o foo o Wa ahls f00 lst In order to pass an assembler file t
230. will typically optimize the access to flag completely away since its code path analysis shows that nothing inside the loop could change the value of flag anyway To tell the compiler that this variable could be changed outside the scope of its code path analysis e g from within an interrupt routine the variable needs to be declared like volatile uint8_t flag Back to FAQ Index 7 3 3 I get undefined reference to for functions like sinQ In order to access the mathematical functions that are declared in lt math h gt the linker needs to be told to also link the mathematical library 1ibm a Typically system libraries like 1ibm a are given to the final C compiler command line that performs the linking step by adding a flag 1m at the end That is the initial lib and the filename suffix from the library are written immediately after a flag So for a libfoo a library 1foo needs to be provided This will make the linker search the library in a path known to the system An alternative would be to specify the full path to the 1ibm a file at the same place on the command line i e after all the object files x o However since this re quires knowledge of where the build system will exactly find those library files this is deprecated for system libraries Back to FAQ Index 7 3 4 How to permanently bind a variable to a register This can be done with register unsigned char counter asm r3 See C Names Used in A
231. y running reconf and doconf 10 Perform a make distcheck and make sure it succeeds This will create the snapshot source tarball This should be considered the first release candidate 11 Upload the snapshot tarball to savannah 12 Announce the branch and the branch tag to the avr libc dev list so other devel opers can checkout the branch Note CVS tags do not allow the use of periods 7 Generated on Tue Feb 15 16 09 56 2005 for avr libc by Doxygen 7 6 Release Numbering and Methodology 157 7 6 2 2 Making a release A stable release will only be done on a branch not from the cvs HEAD The following steps should be taken when making a release 9 10 Make sure the source tree you are working from is on the correct branch cvs update r avr lib lt major gt _ lt minor gt branch Update the package version in configure in and commit it to cvs Update the gnu tool chain version requirements in the README and commit to CVS Update the ChangeLog file to note the release and commit to cvs on the branch Add Released avr libc lt this_release gt Bring the build system up to date by running reconf and doconf Perform a make distcheck and make sure it succeeds This will create the source tarball Tag the release _ lt patch gt is not given if this is the first release on this branch cvs tag avr lib lt major gt _ lt minor gt _ lt patch gt release Upload the

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