[Mike Betts]

Originally Posted by Andrew Blair

I'm trying to write some code (actually, modifying Kevin's) with a defunct MPlab, so unfortunately I can't check myself with a test build this weekend. I'm using timer0 as a timer, and have it configured for 10mHz (Or 100 ns). I intend to simply, every 100ns, poll some variables. I have three questions:

1. The interrupt routine is called after the timer overflows. Does it overflow at it's frequency (10mHz)?

2. Do I have to turn off the timer, before I do anything in the interrupt? And will, when executed, the code just enter back into the timer, or do I have to somehow reset it?

3. Did I screw anything else up?

Thanks, interrupts are scary.

  
void Timer_0_Int_Handler(void)
{
 // this function will be called when a timer 0 interrupt occurs
unsigned char tenth_micro_seconds;
unsigned int micro_seconds;
tenth_micro_seconds++;
 if (tenth_micro_seconds>=10)
 {
  micro_seconds++;
 }
}

]

Andrew,

The biggest problem that jumps out at me is that your variables (tenth_micro_seconds and micro_seconds) are local to your interrupt handler.

They must be staic, volatile and initialized properly.

See section 1.10 of K&R and 2.9.2.1 in the C18 Compiler User's Guide.

Mike