[fpc-devel] AVR embedded Atmega 328p interrupts

Andrew Haines andrewd207 at aol.com
Sun Nov 29 23:35:29 CET 2015

On 11/29/2015 02:13 PM, Jeppe Johansen wrote:
> Not sure the timer initialization is right, but it looks ok.
> One thing you need is the interrupt procedure directive:
> procedure TIMER0_overflow; interrupt; public name 'TIMER0_COMPA_ISR';
> Otherwise it'll probably reset at some point.
Ok I got it to work. I have an interrupt:
procedure TIMER0_COMPA; noreturn; public name 'TIMER0_COMPA_ISR';

and the timer is setup with:
procedure TimerInit;
   TCCR0A := TCCR0A or (1 shl WGM01);
   OCR0A := $F9;
   TIMSK0 := TIMSK0 or (1 shl OCIE0A);
   TCCR0B := TCCR0B or 5;//scale  5 = Clock / 1024

The keywords "interrupt" or "noreturn" seem to have the same effect but 
are mutually exclusive.

Without the interrupt or noreturn keyword, TIMER0_COMPA is only called 
once and presumably a crash or infinite loop starts somewhere. ( return 
is causing an error?)
With the interrupt or noreturn keyword and those timer settings, the led 
blinks at the edge of human detection. Success!

Setting interrupts for TIMER0_COMPB and TIMER0_OVC have no effect; they 
are never called. I'm probably not understanding some of how to 
configure timers.



More information about the fpc-devel mailing list