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Timer increases, but variable not ...

Hello, I have a problem with this code:

void test(void)
{
  unsigned long time_start, time_diff;
  unsigned int x=2;

  time_start = timer_value;

  while (x<5)
  {
        time_diff = timer_value;
        if (time_diff-time_start >= 2ul) x=5;

	//  printf("%X\n", time_diff-time_start);
  }
}

timer_value is incremented by Timer T0 10 times a second (IRQ-Routine). This part of code should wait for approx. 0.1 .. 0.2 seconds. But if there is no printf-Command timer_diff doesn't increment. If I stop the Debug-Mode of uVision and take a look at timer_value then it really increased, but time_diff still got the same value as time_start. Why?
If the printf-Command is included, everything works fine ...

Thanks for any hint

Torsten

0 Mik Kleshov over 20 years ago

You probably need to declare timer_value as volatile.

- mike
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0 Torsten Schmidt over 20 years ago in reply to Mik Kleshov

Thanks a lot. Now it works... I'v tried the volatile-thingie before my post, but on timer_diff, not on timer_value *g*

Torsten
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0 Drew Davis over 20 years ago in reply to Torsten Schmidt

timer_value needs to be declared volatile because it is the item that can be changed by something outside the scope of this routine -- that is, the timer hardware itself. Declaring timer_diff volatile does not help because this variable, unlike timer_value, is affected only by code in this procedure itself.

timer_diff is likely optimized away completely in this routine.
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