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help needed on arm7 timer interrupt

duoduo duoduo
Note: This was originally posted on 15th January 2009 at http://forums.arm.com

Dear all !
     i am trying to use a timer interrupt to call a function in an ARM7 platform.i hope this timer interrupt can happen in a 320 microseconds interval.however,i found that when i make the interval less than 11 milliseconds exception happened.
     11 milliseconds is too slow for me.why this happened?can somebody help?many thanks!

additional:i made a big mistake in my description, mixing up microseconds with milliseconds. really sorry.
  • 0
    Note: This was originally posted on 16th January 2009 at http://forums.arm.com

    thanks a lot jacob
    i check my codes and it seemed as if the timer interrupt could not my "non-interrupt code would never run".
    your words made me firmly believe that my needed 320  microseconds is not too fast for an ARM7 chip.thank you again.
  • 0
    Note: This was originally posted on 16th January 2009 at http://forums.arm.com

    i debug step by step and found where exception happened:when i used 320  microseconds and  the routine came to the end of a function, i.e. the statement "return SUCCESS", it stopped there, after a while Undefined instruction exception happened.
    and when i used 11  milliseconds ,it ran well.
    why?can anybody help?
  • 0
    Note: This was originally posted on 28th January 2009 at http://forums.arm.com

    In many controllers, the timer keeps running even if you stop at a breakpoint.. so you cant really debug timers using single stepping.. you could probly check if that is the case here.. can you tell us the name of the controller you are using?
  • 0
    Note: This was originally posted on 3rd February 2009 at http://forums.arm.com

    arm7
    s3c44b0
  • +1 Arm Employee Badge
    Note: This was originally posted on 15th January 2009 at http://forums.arm.com

    I'm not sure, but I think you may have mixed up your units somewhere along the line. 11 microseconds is considerably smaller than 320 milliseconds :)

    Setting the timer interval to a value that is too small will not itself cause an exception (other than the interrupt itself). Usually, this would cause a timer event to occur before the previous event had completed, which would result in the interrupt handler appearing to run in a continuous loop; your non-interrupt code would never run. There are situations and configurations which could result in an exception, but I don't think you are seeing this.

    For reference:
    The typical ARM7 microcontroller clocks at about 60MHz. One cycle at this frequency is about 17 nanoseconds, so your 11 microseconds threshold is about 647 cycles. It is quite possible for an interrupt routine to take that long, so it's likely that you're seeing the infinite interrupt loop that I described. However, 320 milliseconds is much longer than that so you have plenty of head room :-)

    I hope that helps,
    Jacob