INTERRUPT TIMED CLOCK ABSTRACT: This laboratory will
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1. In addition to the above guidelines it is important to keep in mind that this timer is emulated Therefore the timed periods will not always be accurate Due to overhead involved in running the debugger the timer may run slightly fast or slow Thus it is usually best to try and minimize overhead if you want the timer to approximate the real device In other words if you are trying to run a clock timing every tenth of a second might create excessive overhead and force the timer to ruin very slowly with each tenth actually taking about a quarter of a second However timing every minute would create very little overhead so the timer might actually run faster than a real clock The moral of the story is set the counter preload registers as if there were 125 000 ticks per second and expect the timer to go a little faster or slower than you set it to Timer register addresses The addresses of the emulated timer registers are TCR timer control register 10021 TIVR timer interrupt vector register 10023 CPRH counter preload high 10027 CPRM counter preload medium 10029 CPRL counter preload low 1002B TSR timer status register 10035 TSRW timer status register write only 10037 If you copy the clocklab com file to your directory you will be able to use an easy command to start up the debugger without needed the File Command 68230 com discussed above i e by typing db68k c clocklab lt your_prog_name gt This means all of the f2. interrupt H2 status set to 1 to clear interrupt H1 status set to 1 to clear interrupt set appropriate pin functions reload counter when countdown through zero use pre scaler 32 stop start timer 64 4 100 the address of the counter preload registers YOU FIGURE OUT FOR 1 10 th SECOND status of timer ZDS bit 1 indicates rollover set to 0 to clear timer interrupt These registers are located in memory as follows PGCR 10001 PSRR 10003 PADDR 10005 PBDDR 10007 PIVR 1000B PACR 1000D PBCR 1000F PADR 10011 PBDR 10013 PSR 1001B TCR 10021 TIVR 10023 CPRH 10027 CPRM 10029 CPRL 1002B TSR 10035 HINTS NOTES ON DEBUGGING YOUR LAB 1 Put your display routine in your main program loop Display timing is not critical and will slow down your interrupt service routine DO NOT call exceptions TRAP s in your interrupt service routine 2 IMPORTANT NOTE You have to set an option in the debugger to properly process interrupts At the command line type Debugger Options General Exceptions Normal or Debugger Options General Exceptions Report to enable interrupts The default is Debugger Options General Exceptions Stop This command specifies what the debugger does on an exception As one would guess Stop will simply display a message in the journal window and NOT process your exception For debugging I would recommend the Report option it flashes a message in the journal window and processes th
3. We have gotten so much e mail that we doubt that we can reply to all messages in the forseeable future Some simple things you can do 1 write a very small minimalist program to show that you can start the 68230 and handle interrupts The following program is of that type and works very well include io s include the debugger i o routines org 1000 start program at 1000 Main move b 2 D5 set variable seconds move 1 intr 100 load the address of the interrupt service routine into the 68000 vector location 3256 decimal 64x4 move 1 125000 d0 put the counter preload into d0 lea 10025 a0 now put the address of the counter into a0 movep 1 d0 a0 use movep to load the counter move b 64 10023 load the vector into the TIVR move b al 10021 load the TCR Setting a just sets the 768230 to the appropriate mode The 1 in bit 0 starts the timer loop nop now just do the same thing over n over bra loop intr add 1 D5 this is the interrupt service routine rte done end Main If this program does not work you have other problems and should follow the following steps 2 When you are getting debugger problems with files opening and so forth Consider the following Start the debugger without any arguments i e just type db68k When the debugger has started up type File Command clocklab com If the files load correctly then your com files are NOT the cause of the problem If the files do not load correctly copy new
4. a gt In attempting to begin lab 6 we have encountered a number of problems gt gt 1 How is input to be accepted from the user The problem of gt decimal to hex conversion seems large Are we supposed to accept it in gt the HH MM SS format as listed in the lab and if so how is that input to gt be converted to hex so that it can be properly dealt with by the rest of gt the program As far as input is concerned putting it into a register or memory with the debugger is perfectly fine and you do not need to convert to write an input conversion routine gt gt 2 Along those same lines how is the information to be converted gt to ASCII for output For example if you have counted 30 minutes and thus gt need to ouput a 30 to the screen how do you get a 1E hex to a 51 anda gt 48 decimal for output as ASCII characters to the screen Now this is more interesting and a lab requirement The wasiest thing is to convert each number INDIVIDUALLY to an ASCII character put them in memory somewhere and use PutString to output them gt gt 3 Also it appears the 68230 has four interrupt lines H1 H4 gt which are Port Interrupt Vectors You have these listed as being set in gt the lab desciprtion however are those the interrupts used or is it the gt TIVR interrupt that is used You had also mentioned in class that the gt 68000 should respond only to the Level 5 interrupt from the 68230 yet I gt cannot see how that relat
5. function of the 68230 s TIVR What is the vector number for your timer request See Ford amp Topp p 758 The 68230 TIVR contains the vector number that the 68230 returns to the 68000 as part of the interrupt acknowledge cycle This vector is used with the exception vector table to determine the address of the routine that should service this interrupt 2 Describe the function of the zero detect field of the 68230 s TCR According to Ford amp Topp page 603 the Action on Zero Detect field controls what happens when the timer counts down from zero In Chapter 12 the 68230 was programmed with 100 which simply tells the counter to count and do nothing when it passes through zero However in Chapter 14 we typically used 101 which says to generate vectored interrupts on zero detect Thus everytime the counter passes through zero it will generate an interrupt The 68000 will then ask the 68230 for the vector number which was previously programmed into TIVR to determine the address of the appropriate Interrupt Service Routine 3 When if ever does your main program terminate An interrupt driven main program should never terminate It should continually keep running in an infinite loop or something similar 4 What does the instruction BCLR 0 TCON do TCON is the address of the 68230 s Timer Control Register This is the 68230 timer enable bit The 68230 timer is enabled when this bit is set to 1 it is disabled when the bit is set t
6. necessary 9 Interrupt routines a reset b terminate The terminal display function can be done using HexOut SETTING UP THE 68230 PI T Since this is a complicated chip and the setting of certain registers requires a detailed knowledge of how the chip is connected to the 68000 I will provide you with a guide to setting up some of the 68230 control registers REGISTER BIT S SET TO DESCRIPTION PGCR S 3F 7 6 0 5 1 enable H3 and H4 interrupts 4 1 enable H1 and H2 interrupts 3 2 1 0 1 make H1 H2 H3 H4 high true PSRR 18 PIVR 44 PADDR PBDDR PACR 82 PBCR 82 PBDR PADR PSR TCR A1 TIVR vector CPRH CPRM CPRL INTERRUPTS TSR N eN all all N OrFNUDNORN UA amp oO 4 e N nNOrO x xA KM RFPODOOFRrKXFOGDVCOFROF 0 1 0 1 0 1 0 1 Orok 0 1 64 0 1 no DMA set up interrupt pins H1 gt H2 gt H3 gt H4 priority H1 vector at 68 0 4 110 H2 vector at 68 1 4 114 H3 vector at 68 2 4 118 H4 vector at 68 3 4 11B all pins LED s are outputs all pins switches are inputs mode 0 submode 1X mode 0 submode 1X H2 is output pin LED above H1 no H2 interrupts accept H1 interrupts don t care mode 0 submode 1X mode 0 submode 1X H4 is output pin LED above H3 no H4 interrupts accept H3 interrupts don t care input port output port status register for H1 H2 H3 H4 H4 status set to 1 to clear interrupt H3 status set to 1 to clear
7. 230 registers Note that the 68230 only has registers at odd addresses Any attempt to display an even address such as 10022 will generate a BUS ERROR LAB 6 WRITE UP FORMAT 1 Include the normal title page 2 Include a Pseudo code description of your program Be specific about 68230 initialization procedures and turning on off interrupts during routines in your pseudo code 3 Include an ASSEMBLER listing of your complete program 4 Include a short description in English of how your debugger screen should look Also include a Debugger screen showing the clock 5 Answer the following questions Note The 68230 is described in Section 12 4 of Ford amp Topp in great detail 1 Describe the function of the 68230 s TIVR What is the vector number for your timer request See Ford amp Topp p 758 2 Describe the function of the zero detect field of the 68230 s TCR 3 When if ever does your main program terminate 4 What does the instruction BCLR 0 TCON do TCON is the address of the 68230 s Timer Control Register Consider the following interrupt service routine ISR for a 68230 driven digital clock similar to your lab TIMER MOVE W 2700 SR 7 a MOVE L A0O SP ADDO W 1 TOT TIME LEA TBASE AO BSET 0 TSR A0 lt Why do you need this instruction MOVE L SP A0 RTE TOT TIME DS W 1 TBASE EQU 10021 TSR EQU 20 5 Why do you need the indicated instruction 6 What is the function of instruction
8. INTERRUPT TIMED CLOCK ABSTRACT This laboratory will introduce the student to the generation of interrupts using a programmable timer the handling of an interrupt and the priority of interrupts This laboratory will implement a digital clock using interrupts timed at 1 10th second intervals A 68230 programmed interface timer PI T chip emulated by the debugger using debugger macros will be used to program the timer Note that the 68230 s interrupt MUST be reset by clearing the ZDS bit in the interrupt service routine At the start of the program you should accept an input time hours minutes seconds Your program will consist of an interrupt service routine that will update the time and display it on the screen every 1 10 th of a second i e HH MM SS D I WILL LEAVE IT TO YOUR OPTION AS TO WHETHER YOU IMPLEMENT A 12 HOUR OR A 24 HOUR CLOCK This will require that you convert your clock data from hex to ASCII OPTIONAL To make the program more interesting you can program it to beep once for every hour i e beep once for 1 00 00 0 twice for 2 00 00 0 etc The beeping sound can be generated by sending a 07 to your terminal The program should have the following programming sequence 1 Request the input time 2 Store the input time 3 Initialize registers in the PI T 4 Reset the 68230 status bits 5 Set up the interrupt vectors 6 Enable the timer 7 Enable interrupts by changing the status register 8 Generate displays and beeps as
9. e exception just as you would expect When you actually run your clock program use the Normal option which processes the exception the same way the Report option does BUT without the message to the journal window This info is in the debugger manual on page 4 2 3 Test a first version of your program without any fancy output A major problem is often that your program is so complicated that you cannot debug it Formatted output often causes problems 4 You can examine the 68000 exception vector table using the debugger s Memory Display commands You can also examine the 68230 registers Note that the 68230 only has registers at odd addresses Any attempt to display an even address such as 10022 will generate a BUS ERROR Emulation Code User s Manual the 68230 PI T Information on the 68230 PI T can be found in the text book on pages 399 415 The information presented here is intended only to make writing code that uses the 68230 emulation easier What do I need to use the 68230 emulation You will need to load the file called 68230 com into the debugger This file can be loaded by typing from the debugger command line File Command 68230 com I have put it into home courses 282 pub How can I use the timer You can use the timer in two modes interrupt mode or polled mode The polled mode works similarly to the polled I O from the keyboard First the timer is set up by writing to the counter preload registers and the timer contro
10. e the proper format of pseu gt docode They wrote either the source file with comments for most gt instructions or the paragraphs of statements So I d like to split gt pseudocode description into two parts one for the format the other gt for the logic sometimes this part will actually graded by reading gt the listing instead of the pseudocode Is that OK That seems fair I would take off 5 points for the format and allocate the rest for the logic the most important part gt 2 Some students stated that they couldn t terminate their programs gt However you have instructedO them how to do that Shall I take off gt any points for that That s OK Since we have implemented Exception processing the normal Trap 0 wll not work for them So don t take anything off for that
11. es to anything in how the 68230 is set up It gt seems to me that upon counting down to 0 it will cause an interrupt which gt will jump to the vector at address 100 the way the 68230 is set up in gt the lab Is this correct This is where you need to read section 12 4 of the textbook for a lot of detail The H1 thru H4 interrupts are for other purposes However if you carefully read the description of the Port Interrupt Vector Register on page 762 of the text this should help You may also want to look at the section of the text titled A Standalone Timer Library beginning on p 607 The routines initTimer there may be useful Potentially more useful is the routine initIntTimer on page 759 gt In example 14 5 pg 760 what does the following line of code do gt MOVE L clock vClock W gt gt I m having trouble compiling this example because of this instruction How gt is it linking the timer to the interrupt service routine It does not link the timer to the interrupt service routine It simply loads the exception vector it really is MOVE L clock 100 our assembler probably does not like the vClock w Change it to MOVE L clock vclock This instruction is putting the address of the interrupt service routine into the proper place in the exception vector table 100 for a user interrupt vector of 64 The process of what is happening is described in detail on pages 776 777 of the text under Interrupt Acknowledge Bus Cycle
12. files from home courses 282 pub Also if you get a file access error for 68230a com be sure that you have changed the 68230 com in clocklab com to 68230a com 3 If your com files pass test 2 above and you get an error message when you try to run your program Specifically you might get something like Invalid vector number Must be 0 to 255 or none 00000000 gt 0005000 gt 00000000 gt 0005001 gt 00000000 gt 0005001Program Interrupt Add Once ccyc 2 TIVR or anything else that is referring to TIVR I suspect that these errors are caused by a global variable inside the debugger interferring with a variable of the same name in your program The global variable is changing causing changes to the values you are loading into the 68230 and interferring with the macros Change the name of the variables in your program and THIS problem SHOULD go away Sorry this took so long but I had my computer crash twice while typing this up and lost both previous messages I sent You can modify the suggest grading scheme as appropriate LAB 6 WRITE UP FORMAT as sent to the students 1 Include the normal title page 10 POINTS 2 Include a Pseudo code description of your program Be specific about 68230 initialization procedures and turning on off interrupts during routines in your pseudo code 30 POINTS Be sure that the pseudocode describes how the 68230 is initialized and how the program works in detail This might be accompanied by a write
13. ist of an interrupt service routine that will update the time and gt display it on the screen every 1 10 th of a second i e HH MM SS D I WILL gt LEAVE IT TO YOUR OPTION AS TO WHETHER YOU IMPLEMENT A 12 HOUR OR A 24 HOUR gt CLOCK This will require that you convert your clock data from hex to gt ASCII We will accept almost any format 20 POINTS TOTAL FOR DISPLAY 5 points if no debugger screen of the display format 8 points for display using HexOut instead of a digital format GENERAL POINTS This laboratory will implement a digital clock using interrupts timed at 1 10th second intervals A 68230 programmed interface timer PI T chip emulated by the debugger using debugger macros will be used to program the timer Note that the 68230 s interrupt MUST be reset by clearing the ZDS bit in the interrupt service routine At the start of the program you should accept an input time hours minutes seconds Your program will consist of an interrupt service routine that will update the time and display it on the screen every 1 10 th of a second i e HH MM SS D I WILL LEAVE IT TO YOUR OPTION AS TO WHETHER YOU IMPLEMENT A 12 HOUR OR A 24 HOUR CLOCK This will require that you convert your clock data from hex to ASCII 55 30 5 Answer the following questions 5 POINTS EACH The student answers do not need to be as detailed as mine Note The 68230 is described in Section 12 4 of Ford amp Topp in great detail 1 Describe the
14. l register in that order Then the timer can be used by starting the timer checking the timer status register until it signals the end of the given time and then clearing the timer status register with a direct clear to reset the timer The interrupt mode operates much differently To use this mode the timer interrupt vector register must be properly set first Then the counter preload registers can be set and finally the timer control register can be initialized The interrupt vector register should not be changed from its initial value without stopping the time and starting the entire process from scratch In summary polled I O mode 1 initialize counter preload registers initialize timer control register start the timer poll the timer status register when finished direct clear the TSR YOU MUST WRITE TO TRSW to time the same period again goto step 3 Dye en interrupt I O mode 1 initialize timer interrupt vector register 2 initialize counter preload registers 3 initialize timer control register 4 start the timer 5 The timer will continue timing the same period until stopped 6 When finished stop the timer by writing to the timer control register Steps 2 and 3 for the polled I O case or steps 3 and 4 for the interrupt case can be done together because they both involve writing to the timer control register How do I set the period I want to time You always set the period you want to time by writing to the three c
15. o zero Specifically the given instruction then stops the 68230 s timer Consider the following interrupt service routine ISR for a 68230 driven digital clock similar to your lab TIMER MOVE W 2700 SR _ a MOVE L AO SP ADDQ W_ 1 TOT_TIME LEA TBASE AO BSET 0 TSR AO lt Why do you need this instruction MOVE L SP A0 RTE TOT_TIME DS W_ 1 TBASE EQU 10021 TSR EQU 20 5 Why do you need the indicated instruction This was Problem 19 f Chapter 14 of Ford amp Topp According to F amp T this instruction negates the timer interrupt request This is incorrect According to page 605 of F amp T this is the Zero Detect Status ZDS bit If ZDS 1 the counter has reached zero otherwise the timer is still running or is not enabled After the ZDS has been set to 1 by the counter reaching 0 it must be manually reset to 0 If it is not reset to zero it will continually remain at one and cannot be used to detect any further zero crossings of the timer Note that the timer continues to run The TSR only monitors the zero crossings the TCR controls the timer 6 What is the function of instruction a The instruction labeled a changes the interrupt mask to 111 which disables all exteral interrupts Note that the 68000 MUST be in supervisor mode for you to be able to do this gt After going over the reports I ve got so far I found the gt following situations existing gt 1 A few students still didn t giv
16. ollowing files should be in your directory 68230 com acia com iodorm com clocklab com extra com The extra com file just sets the usp and ssp If you want to do this tyourself you can skip this file HINTS NOTES ON DEBUGGING YOUR LAB 1 DO NOT call exceptions TRAP s in your interrupt service routine 2 IMPORTANT NOTE You have to set an option in the debugger to properly process interrupts At the command line type Debugger Options General Exceptions Normal or Debugger Options General Exceptions Report to enable interrupts The default is Debugger Options General Exceptions Stop This command specifies what the debugger does on an exception As one would guess Stop will simply display a message in the journal window and NOT process your exception For debugging I would recommend the Report option it flashes a message in the journal window and processes the exception just as you would expect When you actually run your clock program use the Normal option which processes the exception the same way the Report option does BUT without the message to the journal window This info is in the debugger manual on page 4 2 3 Test a first version of your program without any fancy output A major problem is often that your program is so complicated that you cannot debug it Formatted output often causes problems 4 You can examine the 68000 exception vector table using the debugger s Memory Display commands You can also examine the 68
17. ounter preload registers As detailed in the text book all three registers can be set at once using a single MOVEP instruction although three MOVE B instructions will also work The timer ticks 125 000 times per second so the proper number to load into the registers can be calculated by multiplying the number of seconds by 125 000 How do I initialize the timer control register You can initialize the timer control register by doing a MOVE B command The number written to the control register determines the mode that the timer operates in The settings should be made as follows action on zero detect first three bits should be either 100 for polled or 101 for interrupt counter load fourth bit can be 1 to rollover or 0 to reset from preload clock control sixth seventh bits should always be 00 timer enable eighth bit can be 1 to start or 0 to stop timer Additional Guidelines The operations should always be done in the order specified This means that the timer interrupt vector register should never be initialized after you start the timer Also anytime you want to change a parameter the timer should be stopped the parameter changed and then the timer restarted Changing a parameter while the timer is running could do anything from having no effect to sending the 68000 into random code sections it is very important that you stop and restart the timer when changing parameters to give the emulation code a chance to recognize your changes
18. up gt This laboratory will implement a digital clock using interrupts timed at gt 1 10th second intervals A 68230 programmed interface timer PI T chip gt emulated by the debugger using debugger macros will be used to program the gt timer We will accept either 1 preload 125000 or 0 1 preload 12500 second interrupts The Interrupt Service Routine ISR can include the display or the display can be in the main program The 68230 should be initialized once exernal to the ISR The ISR should not reset and restart the 68230 everytime an interrupt occurs Several students have done this 10 points if they continually reset the 68230 unless they specifically mention that this was done to overcome problems with the debugger macros You should look to see if they reset the interrupt mask during the ISR This wil only work if the program was started in supervisor mode They may have reset the ZDS bit in the ISR This is not necessary but don t take off any points for it The Lab assignment also said gt At the start of the program you gt should accept an input time hours minutes seconds 5 points if they did not use HexIn or 10040 10042 polled i o 3 Include an ASSEMBLER listing of your complete program 10 POINTS 4 Include a short description in English of how your debugger screen should look Also include a Debugger screen showing the clock According to the lab description gt Your program will gt cons
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