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Re: [avr-gcc-list] Sharing interrupts

From: Erik Christiansen
Subject: Re: [avr-gcc-list] Sharing interrupts
Date: Tue, 9 Dec 2003 10:59:31 +1100
User-agent: Mutt/1.3.28i

On Mon, Dec 08, 2003 at 04:17:50PM -0500, Dave Hansen wrote:
> From: Pablo Bleyer Kocik <address@hidden>
> > I was wondering, is there an easy way to register two interrupt vectors 
> >with the same interrupt handler? The SIGNAL/INTERRUPT macros expand to a 
> >function declaration and function definition header, so it is not possible 
> >to assign function pointers with them.


> Another solution might be to write an assembly ISR to jump to the other 
> ISR. I'm less sure of how this would work, but something like
>   // In a C file
>   {
>      // Do what you gotta do
>   }
>   ; in an assembly file
>   __vector_y:   rjmp __vector_x

In the absence of a direct 'C' language method for pointing two vectors
to the same ISR, it can easily be done in assembler.

   .global log_isr               ; Just like "external"

   .section .vectors,"ax",@progbits
; Interrupt Vector Table
   jmp  _start                   ; N.B. ATmega64 has 2 words/vector.
   ldi   r16,0                   
   rjmp  v_error                 ; Look, they
   ldi   r16,1
   rjmp  v_error                 ; all go to
   ldi   r16,2
   rjmp  v_error                 ; the same ISR.
                                 ; ldi optionally used to indicate
                                 ; which vector was followed.

   jmp   log_isr                 ; This ISR is in another file.



(In this example, v_error causes LEDs on a port to flash a number
indicating which unanticipated interrupt occurred. During debugging it
is sometimes the first indication of a wayward pointer, as it tramples
through the SFRs, enabling interrupts, amongst other forms of mayhem.)

Whether you use gcc, or avr-as directly, the resulting object file is
then linked like any other, and the job is done.


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