RE: Problem initialise timer for 1µs cycle
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RE: Problem initialise timer for 1µs cycle
by folgli
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Hello,
>Because of character problems on the mail I received, I can't see if you >want interrupt each micro-second. >If so, it seems very very fast for that processor. I need to increment a variable every micro-sencond. I am implementing an CANopen stack at the controller. For this I need to increment a variable every micro-second. I have written a test programm to test the timer. The timer basically works.. The interrupt works etc. but I do not know how to configure the timer registers so that I get an interrupt every micro-second. You can find attached the programm files. Perhaps someone can tell me how to configure the timer to get an interrupt every micro-second. Perhaps an additional question. How can I test the Interrupt? I toggle some LED's every interrupt but I think when using a one micro-second interrupt you can not see toggling the LED's any more ;). It is all written in C. Thank you very much!Best regards --- folgli@... <folgli@...> schrieb am Fr, 1.5.2009: I find just this morning your problem about Timer. Because of character problems on the mail I received, I can't see if you want interrupt each micro-second... If so, it seems very very fast for that processor. With 12 Mhz quartz, no PLL, I use an empty function (in C) to delay 2.5 micro-seconds : void Delay_2_5_micro (void) { // nothing to do } That means just call and return from this empty function take 2.5 micro-seconds, measured with oscilloscope. Hope this helps. Joel Von: folgli@... <folgli@...> Betreff: [68HC12] Problem initialise timer for 1µs cycle An: 68hc12@... Datum: Freitag, 1. Mai 2009, 13:56 Hello, I have a problem with using the Timer on a MC9S12DP512. I want to create 1µ second cycles. Every µs I want to increment a variable, but I do not know how to initialise the timer, so that I get a timer interrupt every µs. I hope that someone can help me. Best regards [Non-text portions of this message have been removed] |
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RE: Problem initialise timer for 1µs cycle
by jpdi
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Hi,
As I told you in my precedent mail, I think you can't increment a character each micro-second. The reason is this delay is too short for that processor. As I explained, an empty function (quartz 12 MHz, CPU frequency 6 Mhz) takes 2.5 micro-seconds : EmptyFunction (void) { // nothing to do ! } void main (void) { while (1) { led = 0; EmptyFunction (); led = 1; } } The led will flash about 2.5 micro-second. The micro-processor just have to (Core user guide, instructions JSR and RTS) - (SP) - $0002 -> SP // JSR instruction - RTNh:RTNl -> (Msp):(Msp+1) - subroutine add -> PC - do nothing - (Msp):(Msp+1) -> PCh:PCl // RET instruction - (SP) + $0002 -> SP An interrupt function will take more time, because of some additional things to do : save registers for example... I don't know what is the sequence for interrupt call, but I can see, JUST FOR the RTI instruction (return from interrupt) : - (Msp) -> CCR // recover flags - ((SP) + $0001 -> SP - (Msp):(Msp+1) -> B:A // recover A and B registers - ((SP) + $0002-> SP - (Msp):(Msp+1) -> Xh:Xl // recover X register - ((SP) + $0002-> SP - (Msp):(Msp+1) -> PCh:PCll // recover PC register - ((SP) + $0002-> SP - (Msp):(Msp+1) -> Yh:Yl // recover Y register - ((SP) + $0002-> SP That means RTI restores CCR, B, A, X, PC, and Y. Where RET has 2 things to do, RTI has 5 ! You can see, with the same core frequency, interrupt function will be slower than empty function, because interrupt function has more things to do. So, if you use PLL of the micro-processor, I say for example 24 Mhz core freq, your empty function will take 2.5 / 4 micro-second, 0.63 micro-second. BUT : - because your interrupt function has more thing to do, I can suppose it can't do in less than 1 micro-second. - even if it is ok, your micro-processor will only run under its interrupt service routine. So, for me, forget to increment your character each micro-second : it's too quick. Of course, your timer will interrupt your main process... Even with RTI timer, or the other timers T0...T7. But at which period ? Certainly not at 1 micro-second, I think ! I hope this helps. Joel -----Message d'origine----- De : 68HC12@... [mailto:68HC12@...] De la part de Sven K Envoyé : lundi 18 mai 2009 14:38 À : 68HC12@... Objet : RE: [68HC12] Problem initialise timer for 1µs cycle Hello, >Because of character problems on the mail I received, I can't see if you >want interrupt each micro-second. >If so, it seems very very fast for that processor. I need to increment a variable every micro-sencond. I am implementing an CANopen stack at the controller. For this I need to increment a variable every micro-second. I have written a test programm to test the timer. The timer basically works.. The interrupt works etc. but I do not know how to configure the timer registers so that I get an interrupt every micro-second. You can find attached the programm files. Perhaps someone can tell me how to configure the timer to get an interrupt every micro-second. Perhaps an additional question. How can I test the Interrupt? I toggle some LED's every interrupt but I think when using a one micro-second interrupt you can not see toggling the LED's any more ;). It is all written in C. Thank you very much!Best regards --- folgli@... <folgli@...> schrieb am Fr, 1.5.2009: I find just this morning your problem about Timer. Because of character problems on the mail I received, I can't see if you want interrupt each micro-second... If so, it seems very very fast for that processor. With 12 Mhz quartz, no PLL, I use an empty function (in C) to delay 2.5 micro-seconds : void Delay_2_5_micro (void) { // nothing to do } That means just call and return from this empty function take 2.5 micro-seconds, measured with oscilloscope. Hope this helps. Joel Von: folgli@... <folgli@...> Betreff: [68HC12] Problem initialise timer for 1µs cycle An: 68hc12@... Datum: Freitag, 1. Mai 2009, 13:56 Hello, I have a problem with using the Timer on a MC9S12DP512. I want to create 1µ second cycles. Every µs I want to increment a variable, but I do not know how to initialise the timer, so that I get a timer interrupt every µs. I hope that someone can help me. Best regards [Non-text portions of this message have been removed] ------------------------------------ Yahoo! Groups Links |
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Re: Problem initialise timer for 1µs cycle
by Edward Karpicz
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Joel is right, interrupt every 1us is overkill. Minimalistic interrupt
service routine, even without mandatory flag clear sequency would take 9+8 bus cycles (SWI+RTI). That's 0.68us at 25MHz bus. Add here required timer flag clear and CPU will be almost 100%. If you need 1us counter, then why not using free running TCNT for this purpose? If application allows, then you could set prescaler so that TCNT tick is close to 1us. If you can't, then TCNT readings should be scaled to 1us resolution. If you need wider than 16bits counter, then you could use timer overflow interrupt to increment higher order word of counter and use TCNT as a lower order word of counter. BTW this CanOpen implementation www.canfestival.net doesn't require 1us interrupts. Regards Edward ----- Original Message ----- From: "jpdi" <jpdi@...> To: <68HC12@...> Sent: Monday, May 18, 2009 6:09 PM Subject: RE: [68HC12] Problem initialise timer for 1µs cycle Hi, As I told you in my precedent mail, I think you can't increment a character each micro-second. The reason is this delay is too short for that processor. As I explained, an empty function (quartz 12 MHz, CPU frequency 6 Mhz) takes 2.5 micro-seconds : EmptyFunction (void) { // nothing to do ! } void main (void) { while (1) { led = 0; EmptyFunction (); led = 1; } } The led will flash about 2.5 micro-second. The micro-processor just have to (Core user guide, instructions JSR and RTS) - (SP) - $0002 -> SP // JSR instruction - RTNh:RTNl -> (Msp):(Msp+1) - subroutine add -> PC - do nothing - (Msp):(Msp+1) -> PCh:PCl // RET instruction - (SP) + $0002 -> SP An interrupt function will take more time, because of some additional things to do : save registers for example... I don't know what is the sequence for interrupt call, but I can see, JUST FOR the RTI instruction (return from interrupt) : - (Msp) -> CCR // recover flags - ((SP) + $0001 -> SP - (Msp):(Msp+1) -> B:A // recover A and B registers - ((SP) + $0002-> SP - (Msp):(Msp+1) -> Xh:Xl // recover X register - ((SP) + $0002-> SP - (Msp):(Msp+1) -> PCh:PCll // recover PC register - ((SP) + $0002-> SP - (Msp):(Msp+1) -> Yh:Yl // recover Y register - ((SP) + $0002-> SP That means RTI restores CCR, B, A, X, PC, and Y. Where RET has 2 things to do, RTI has 5 ! You can see, with the same core frequency, interrupt function will be slower than empty function, because interrupt function has more things to do. So, if you use PLL of the micro-processor, I say for example 24 Mhz core freq, your empty function will take 2.5 / 4 micro-second, 0.63 micro-second. BUT : - because your interrupt function has more thing to do, I can suppose it can't do in less than 1 micro-second. - even if it is ok, your micro-processor will only run under its interrupt service routine. So, for me, forget to increment your character each micro-second : it's too quick. Of course, your timer will interrupt your main process... Even with RTI timer, or the other timers T0...T7. But at which period ? Certainly not at 1 micro-second, I think ! I hope this helps. Joel -----Message d'origine----- De : 68HC12@... [mailto:68HC12@...] De la part de Sven K Envoyé : lundi 18 mai 2009 14:38 À : 68HC12@... Objet : RE: [68HC12] Problem initialise timer for 1µs cycle Hello, >Because of character problems on the mail I received, I can't see if you >want interrupt each micro-second. >If so, it seems very very fast for that processor. I need to increment a variable every micro-sencond. I am implementing an CANopen stack at the controller. For this I need to increment a variable every micro-second. I have written a test programm to test the timer. The timer basically works.. The interrupt works etc. but I do not know how to configure the timer registers so that I get an interrupt every micro-second. You can find attached the programm files. Perhaps someone can tell me how to configure the timer to get an interrupt every micro-second. Perhaps an additional question. How can I test the Interrupt? I toggle some LED's every interrupt but I think when using a one micro-second interrupt you can not see toggling the LED's any more ;). It is all written in C. Thank you very much!Best regards --- folgli@... <folgli@...> schrieb am Fr, 1.5.2009: I find just this morning your problem about Timer. Because of character problems on the mail I received, I can't see if you want interrupt each micro-second... If so, it seems very very fast for that processor. With 12 Mhz quartz, no PLL, I use an empty function (in C) to delay 2.5 micro-seconds : void Delay_2_5_micro (void) { // nothing to do } That means just call and return from this empty function take 2.5 micro-seconds, measured with oscilloscope. Hope this helps. Joel Von: folgli@... <folgli@...> Betreff: [68HC12] Problem initialise timer for 1µs cycle An: 68hc12@... Datum: Freitag, 1. Mai 2009, 13:56 Hello, I have a problem with using the Timer on a MC9S12DP512. I want to create 1µ second cycles. Every µs I want to increment a variable, but I do not know how to initialise the timer, so that I get a timer interrupt every µs. I hope that someone can help me. Best regards [Non-text portions of this message have been removed] ------------------------------------ Yahoo! Groups Links ------------------------------------ Yahoo! Groups Links |
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