Output Compare Lab - University of Florida
Contents
1. PMIC_CTRL control register f In any interrupt driven application the global interrupt flag should be the last thing you set during initializations Simply use the sei instruction to set the global interrupt flag to enable the interrupt The processor needs to know what code to execute when an interrupt occurs After an interrupt occurs there is a specific address to which the processor will jump This address is called the interrupt vector address The name of the vector for this interrupt is PORTx_INTn_vect where x and n are defined by you based on the interrupt pin that you selected This vectors value is defined in the Our ATxmegal28A1U Register Descriptions file the included file available from the Software Docs section of the class website In C the vector s values are available in the avr io h file Write an ISR to display a count of how many times interrupt has been executed on your LEDs Be sure to initialize the count to zero and LED pin directions to output FRetabeletibets it sanusitethessuyes the name of the vector that represents it ren The label of the ISR must be the same as what you used in the interrupt rjmp or jmp instruction after the org to the interrupt vector The ISR must end with a reti instruction The reti instruction is a special return statement reserved only for interrupt service routines and is slightly different from a ret instruction By naming your ISR the same as the vector the c2. it I suggest that you start by writing a simple program to read a character using IN_CHAR then write a simple program to output a character using OUT_CHAR and then write program to echo what is received with IN_CHAR by transmitting the read data using OUT_CHAR Write a final simple program to test your OUT_STRING subroutine before finally writing the required program to display the menu and execute the menu specified tasks PART D Interrupt Driven Receiving We have already used interrupts in part A of this lab Now you will use your knowledge to create an interrupt driven echo program 1 Initialize USART as in part C except also enable low level receiver interrupt using CTRLA 2 Turn on appropriate PMIC interrupt level in the control PMIC_CTRL register 3 Write an ISR triggered on a USART receive that echoes the received data to the transmitter Writing an ISR is very similar to writing a subroutine with the main differences of often needing to clear a flag caused by the interrupt and returning with an RETI instead of a RET You will also generally need to push and pop several registers 4 To demonstrate the concept of an interrupt driven program after your initializations toggle an LED forever with a 0 37 second delay in a loop in the main routine and do nothing else At the same time if you type a key on your terminal your program should echo it back inside an ISR The interrupt should now do all the
3. work for you A properly interrupt driven program should have the following format Main Loop Perform Task boas f External event triggers interrupt Branch to Main Loop nd immediatly jump to ISR ISR wows Handle Event Handle event and retum Where you left off t Retum PRE LAB QUESTIONS 1 List the XMEGA s USART registers used in your programs and briefly describe their functions 2 What is the difference between synchronous and asynchronous communication 3 What is the difference between serial and parallel communication 4 List the number of bounces from part A of this lab How long in ms is your delay routine for debouncing 5 What is the maximum possible baud you can use for asynchronous communication if your board runs at 2 MHz Support your answer with the values you would place in any special registers that are needed IN LAB REQUIREMENTS 1 Part A Demonstrate your external interrupt program executing on your board 2 Part C Demonstrate your USART menu program executing on your board 3 Part D Demonstrate your interrupt driven echo program executing on your board 4 Answer any questions your TA may ask you about your hardware and software APPENDIX Using Bray Terminal You will first need to download the Bray program from our website at http mil ufl edu 4744 software Bray exe More information about this program is available at the website https sites google c
4. 2 Character output subroutine OQUT_CHAR This subroutine will output a single character to the transmit pin of the XMEGA s USART system a Check if the previously transmitted character has been completed if not keep checking until it has been completed b Transmit the character passed to the subroutine 3 String output subroutine OUT_STRING This routine will output character strings stored in memory a Read the character pointed to by Z and increment the pointer b If this character is not null call OUT _CHAR and repeat for each non null character that follows otherwise return from the subroutine 4 Character input subroutine IN_CHAR This subroutine will receive a single character from the receiver pin of the XMEGA s USART system a Check if a character has been received if not keep checking until it has been received b Read the character from the receive buffer Write an interactive program to display your favorite activities on any terminal of your choice The menu you will create should look like this your_name s favorite L Movie 2 Book 3 Food 4 Ice cream yogurt flavor 5 Pizza toppings 6 Redisplay menu ESC exit University of Florida Electrical amp Computer Engineering Dept EEL 4744 Summer 2015 Dr Eric M Schwartz 30 Jun 15 Page 3 4 Revision 2 Lab 5 Interrupts and Serial Communication When your program first starts it should display the above menu using OUT_S
5. 5 13 7 regarding external interrupts on the XMEGA chip Then read section 13 13 which discusses the various registers you will need to use 2 Read doc 8331 chapter 12 about the Programmable Multilevel Interrupt Controller PMIC Pay close attention to section 12 5 regarding interrupt levels 3 Connect a single switch to any unused pin of your choice PORTs E or F Be sure that your keypad circuit remains functional for future labs 4 You will initialize XMEGA to trigger an interrupt when a rising edge is detected on the input The interrupt service routine ISR should only execute when the pin value changes from to GND to VCC te GNB However because we are unable to debounce the switches on our board the ISR will fire on both edges Therefore inside the ISR you will have to test the value of the pin and only complete the desired function if the pin is the correct level Your initializations should proceed as follows a Select an interrupt priority level in the interrupt control register PORTx_INTCTRL for a port of your choosing b Select a pin on that same port as a source for the interrupt in one of the interrupt mask registers PORTx_INTnMASK c Be sure to select the data direction for the input pin Do not make assumptions d Select the input sense configuration for the pin you selected in the PORTx_PINnCTRL register Make sure you select sense rising faline edge e Turn on appropriate PMIC interrupt level in the
6. TRING subroutine and then wait for an incoming character When a 1 2 3 4 5 or 6 is received output the corresponding message such as Cookie Monster s favorite food is cookies and redisplay the menu If the received character is an escape ESC character output Done and terminate execution If any other character is received ignore it For readability add a blank line between every message You will need two special characters to cause the curser to move down a line These two characters are carriage return CR and line feed LF The carriage return will move the cursor all the way to the left and line feed will move the cursor to the next line These characters should occur in order at the end of every line In addition an escape character ESC will be used to terminate your program Note On at least one tablet PC last year the ESC key code did NOT return a 1B If this is the case for your computer just pick another key and let Dr Schwartz and your TA know by sending them emails Also document this in your pre lab report Add the following equates to your asm file egu CR 0x0D egqu LF 0x0A equ ESC Ox1B ASCII characters can be represented as a single character in single quotes e g A or a string of characters in double quotes e g this is a string of ASCII characters CR and LF can be represented as r and n The best way to write and debug code is to test as you write
7. University of Florida Electrical amp Computer Engineering Dept Page 1 4 Revision 2 EEL 4744 Summer 2015 Dr Eric M Schwartz 30 Jun 15 Lab 5 Interrupts and Serial Communication OBJECTIVES e Explore and understand microprocessor interrupts In part A of this lab you will use XMEGA external interrupt system e Learn how to utilize asynchronous _ serial communication In part C of this lab you will use XMEGA s USART system to transmit receive characters to from computer terminal as well as write interrupt driven USART routines and explore multitasking REQUIRED MATERIALS e uPAD and Proto Base kit and tools e DAD Diligent Analog Discovery kit e No new hardware e XMEGA documents e doc8331 section 12 13 and 23 e doc8385 section 33 pinout and pin functions YOU WILL NOT BE ALLOWED INTO YOUR LAB SECTION WITHOUT THE REQUIRED PRE LAB PRELAB REQUIREMENTS REMEMBER You must adhere to the Lab Rules and Policies document for every lab PART A EXTERNAL INTERRUPTS In Lab 2 of this course you added switches to your board You had to continuously poll the input port to know the state of the switches Polling wastes processor clock cycles and results in a slow response time if the processor is engaged in another instruction execution task What if you wanted the processor to respond instantly to any changes on an input switch The answer is to utilize external interrupts 1 Read doc8331 sections 13
8. b In this part of the lab you will write a program to send and receive data between uPAD and your laptop using USARTDO You will need to install a terminal program on your laptop to communicate with your board Some examples are Bray Terminal also known as Br y Terminal PuTTY X CTU RealTerm and HyperTerminal Install and familiarize yourself with one of them A description on how to use Bray Terminal is given in the Appendix The example program used in class is available on our web site SCI_Polling asm and can be used as a starting point for your program To successfully complete this portion of the lab I suggest that you create the subroutines functions described below 1 USART Initialization function USART_INIT This function will take care of all of USART initializations a Set the data direction of the PORTD USART bits to the corresponding values for Tx and Rx b For your uPAD PORTQ bits 1 and 3 control the source of the serial signals from the XMEGA Initialize these pins as outputs and output the appropriate values to these to pins c Set the baud rate to 14 400 Hz bits per second by storing the appropriate value in the baud rate registers You can use a program at http tinyurl com lhunuy2 to verify your baud rate calculation but be sure that you know how to calculate these for your lab quiz and exams d Set the USART for asynchronous mode 8 data bits no parity 1 start bit and 1 stop bit
9. fore you read its value Set your breakpoint after you check the pin s level to make sure you are executing the counting only on a rising fame edge 11 Use your DAD s oscilloscope to record the bouncing used in part 10 Submit a screenshot in your lab document PART B ASYNCHRONUOUS SERIAL COMMUNICATION Asynchronous serial communication can be done entirely in software by bit banging For example if you understand the format of asynchronous serial data see class notes and Figure 23 5 in the doc8331 and you want to send data then all you have to do to transmit a block of data on a GPIO pin You would output the following bits at the required frequency or baud rate start bit 8 data bits least significant bit first and then a stop bit This bit banging is NOT part of the lab requirements but is always an option if the processor has no support for serial communication Similarly a receiver can be made by sampling inputs at the appropriate times PART C XMEGA USART System The XMEGA has several universal synchronous asynchronous receiver transmitter USART peripherals One of them PORTD s USARTDO is connected to the USB port labeled on the uPAD through a FTDI USB bridge chip FT232RL See the uPAD schematic and user manual for more information Determine which pins on PORTD are used for USARTDO using table 33 3 in doc8385 alternate pin functions You won t need this info but include this answer in your prela
10. om site terminalbpp After you write your program you will need to configure the Br y terminal as follows 1 With your XMEGA Board powered you will need to determine the virtual serial port that was created To do this University of Florida EEL 4744 Summer 2015 Dr Eric M Schwartz Electrical amp Computer Engineering Dept 30 Jun 15 Page 4 4 Revision 2 Lab 5 Interrupts and Serial Communication a Right click Computer Transmit b Select Properties CLEAR SendFile 0 l 7 CR CR LF c Click Device Manager EERE d Check e anes a COM amp LPT A MI o m2 ma 4 5 associated w1 e W13 ba 5 E z gt 2 Keyboards gt F Mice and other pointing devices Type here to send queued data than press send gt gt ME Monitors E gt EF Network adapters E F Ports COM amp LPT Connected Rs rar Ts 730 Rs OK ia Brother MFC 9325CW Remote Setup Port COM3 5 When Br y terminal receives data it will be a T Communications Port COM1 displayed in the receive section the data can be D USB Serial Port COM4 viewed in ASCII or HEX We will use ASCII Processors gt sp Sound video and game controllers RAeceve CLEAR Reset Courter 13 Counter 0 ee 2 Open up Br y terminal and match the settings that you wrote in your program and the COM Port The quick brown fox jumped over the lazy dog Note Set handshaking not shown below to none Note Select the COM port that you found in
11. ompiler knows how to put the appropriate rjmp jmp instruction in the vector table based on where it locates the actual routine in memory With this jump instruction the processor knows what to execute when your external interrupt occurs You must as always put the origin of your program at Ox200 or beyond This is necessary because the interrupt vectors which we will use from this lab onward are located in the lower 506 addresses of program memory Ox000 0xIFA You would also University of Florida Electrical amp Computer Engineering Dept EEL 4744 Summer 2015 Dr Eric M Schwartz 30 Jun 15 Page 2 4 Revision 2 Lab 5 Interrupts and Serial Communication still need an appropriate jmp or rjmp instruction at org 0x0 The 0x0 address is the reset interrupt vector which cause your program to start executing at the address corresponding to the label for this jmp or rjmp instruction 9 Make sure your interrupt routine is working correctly by putting a breakpoint inside of it Remember the interrupt will seem to fire on both edges because of bouncing 10 Real switches bounce so the count will probably be wrong Record the number of bounces that you see when the switch goes from low to high and from high to low Do this a few times to see if it is always the same Put the shortest possible delay routine inside your ISR The delay should be near the start of the ISR in order to give the pin time to stop bouncing be
12. the Device Manager The Atmel board will show up under USB Serial Port It is COM4 in this screenshot Note that the values are not what you need for your lab ef Terminal v1 9b 201301168 by Bry foanccl COM Port Baud rate Data bits Parity Stop bitsy gt Handshaking Co 14400 5 500 eG none 4 f none a coma e0 19200 e ii re M odd A ATSACTS a 2400 28800 128000 C een 1 5 XON4 OFF About __COMs e a30 3e400 c 256000 7 M mark M RTS CTS x0N XOF Quit 9600 56000 C custom 3 C space ce f ATS onTa invet 3 Select Connect on the top left If everything is installed correctly you should NOT get a warning and be ready to transmit and receive data 4 There are two ways you can transmit data to your XMEGA a Single Key Press Place your cursor at the bottom of the Br y terminal in the Transmit section and begin typing Transmit CLEAR Send File 0 al CR CR LF Macros Set Macros ha M2 3 wE M5 M13 M14 5 E MIr mE here to send one character at 4 time Connected Ax foe Ts 90 RAs OF b Send Queued Data Place your cursor in the white box and type a message when done press gt Send on the right side not shown below to send the entire message
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