[fpc-devel] AVR embedded Atmega 328p interrupts

[Andrew Haines]

Hi,  I am experimenting with the avr embedded compiler from trunk and am 
trying to set an interrupt. I am not sure how to do it. The interrupt I 
want to change is TIMER0_COMPA_ISR.

I see in the startup code there is:
.weak TIMER0_COMPA_ISR

and later there is:
.set TIMER0_COMPA_ISR, Default_IRQ_handler

I have in my test project added a procedure:
procedure TIMER0_overflow; public name 'TIMER0_COMPA_ISR';
begin
   ToggleLED;
end;

OK I'll just include my test program. I am using an arduino duemilanove 
clone. I got most of the code from:
https://sites.google.com/site/qeewiki/books/avr-guide/timers-on-the-atmega328

Anyway there is no LED visible. I have verified using a delay in the 
main loop toggling the LED works.

What am I not doing, or doing wrong? And btw it's awesome that I can do 
anything at all on this controller!

Thanks,

Andrew

program test;
{$mode objfpc}{$H-}
{uses
   ATmega328P;}
const
   PIN13 = $20;
   WGM01 = 2;
   CS02 = 2;
procedure ToggleLED;
begin
   PORTB := PORTB xor PIN13;
end;

procedure TIMER0_overflow; public name 'TIMER0_COMPA_ISR';
begin
   ToggleLED;
end;

procedure TimerInit;
begin
   TIMSK0:= 1 shl TOIE0; // 1
   TCNT0:=0;
   TCCR0A := TCCR0A or 1 shl WGM01;
   TCCR0B := TCCR0B or 1 shl CS02; // 1 shl 2 = 4
   OCR0A:=$F9;

   TIMSK0:= TIMSK0 or 1 shl OCIE0A;
   asm
     sei;
   end;
end;

begin
   DDRB := DDRB or $FF;// PIN13;
   TimerInit;
   while True do
   begin
     asm
      nop;
     end;
   end;
end.