RE: [avr-gcc-list] Problem with timing

[Dave Hansen]

From: Juraj <address@hidden>
[...]
> Problem is - times are not always 500ms, some of periodes are shorter.

A couple problems with this code:

1) Access to multi-byte variable ms_timer is not atomic.  You must disable 
interrupts while accessing the variable in main-line code

2) You don't account for overflow in ms_timer, e.g. when ms_timer = 
0xFFFFFE10, then koiec will be set to 0x00000004, and the ms_delay function 
will return immediately.

Something like the following (untested) code might help:

  void ms_delay(uint16_t delay)
  {
     uint32_t timer;
     uint32_t start;
     uint32_t elapsed;

     cli();
     start = ms_timer;
     sei();

     do
     {
        cli();
        timer = ms_timer;
        sei();
        elapsed = timer - start;

     } while (elapsed < delay);
}

HTH,
  -=Dave

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