AVR-Chat

> --- In AVR-Chat@yahoogroups.com, "Tim Mitchell" <tim@...> wrote:
>> And remember to save SREG in interrupt routines.
> Unless, of course, it isn't modified.  Although usually not the case, it
> is possible to construct an ISR that does not modify SREG.  Take, for
> example, this one that toggles an output on each external interrupt
> (assuming A.7 is set to be an output and that the device supports port bit
> toggling by writing to the PINx register).
>
> .global INT0_vect
> INT0_vect:
>   push r24
>   ldi r24, 0x80
>   out _SFR_IO_ADDR(PINA), r24
>   pop r24
>   reti
>
> Another caveat for ISRs is that you *cannot* rely on r1 being zero in an
> ISR as you can in a "normal" routine.  Moreover, if you call any C
> functions from an ISR (usually not recommended) you must set r1 to zero
> before calling any C function.
>
> Don Kinzer
> ZBasic Microcontrollers
> http://www.zbasic.net
>

Very informative thread! Much appreciated...

Jim Wagner
Oregon Research Electronics