[avr-gcc-list] TINY13 PWM behavior stumps me.

[Jim Brain]

I have a chunk of code that operates fine on larger AVR8s, but does not 
seem to operate on the T13.  Just wondering if it's me (could be, this 
is the first time I have used such a small AVR8), or the uC...

A snippet:

static volatile uint8_t i = 0;

int main(void) {
  DDRB = _BV(PB0) | _BV(PB1);
  TCCR0A = _BV(COM0A1) | _BV(COM0B1) | _BV(WGM00);
  TCCR0B = _BV(CS00);
  while (1) {

      while(!(TIFR0 & _BV(OCF0A))) ;
      TIFR0 |= _BV(OCF0A);
      if(i == 2) {
        i = 0;
      }
          OCR0A = 192;
        else
          OCR0A = 64;
      i++;
}

When I run this on a larger AVR8, I get 192/64 split on the output, but 
the T13 just shows the first value on the OCR0A output (192, in this case).

I changed the loop to be:

  while (1) {
    for(i = 0; i < 2;i++) {
      while(!(TIFR0 & _BV(OCF0A))) ;
      TIFR0 |= _BV(OCF0A);
        if(!i)
          PWM1_OCR = 192;
        else
          PWM1_OCR = 64;
      }
}

And that shows random values (64 or 192, but in random arrangements, not 
alternating...)

Obviously, this code is non optimal (my original code was an ISR), but I 
thought I'd try to simplify to see if I could figure out the issue.

JIm


-- Jim Brain address@hidden www.jbrain.com