Re: M68K C Interrupt Handler

["clifftsai" <clifftsai at minecard dot com dot tw>]

Hi:
    I wanna how do  you know the compiler will save other register
autimatically?
    Thanks!

----- Original Message -----
From: "Peter Barada" <pbarada@mail.wm.sps.mot.com>
To: <HollaA@HPD.Abbott.com>
Cc: <crossgcc@sources.redhat.com>
Sent: Wednesday, January 17, 2001 12:14 AM
Subject: Re: M68K C Interrupt Handler


>
> >Does anyone know how to write  m68k interrupt handlers  in C?  My
(possibly
> >incorrect/incomplete) understanding of the  issues are that:
> >(1) Normal  function calls generated by the compiler will not work as
> >interrupt functions,
> >(2) I need to save all registers,
> >(3) I can now execute my handler specific C code including any HW
specific
> >start-of-interrupt and end-of-interrupt processing,
> >(4) I need to restore registers,
> >(5) I need to do a return from interrupt (rte).
>
> It's trivial to write an interrupt handler in assembler that calls out
> to your C interrupt function for the 68k:
>
> ASM_IRQ_handler:
> moveml %a0/%a1/%d0/%d1,-(%sp)
> jsr C_IRQ_handler
> moveml (%sp)+,%a0/%a1/%d0/%d1
> rte
>
> You only need to save a0/a1/d0/d1 since all the other registers are
> saved/restored by the compiler, and the SR register is already on the
> stack from the interrupt itself.  Since you mention a straight m68k,
> there's no FPU to worry about.
>
> Of course you'll have to determine the syntax that your assembler
> understands for movem.  I've seen it using as above, and also as:
>
>         movm.l #0xyyyy,-(%sp)
>
> where 'yyyy' is the bit mask in the movem instruction.  See what your
> C compiler cranks out at the start/end of functions for an idea....
>
> --
> Peter Barada                                   Peter.Barada@motorola.com
> Wizard                                         781-852-2768 (direct)
> WaveMark Solutions(wholly owned by Motorola)   781-270-0193 (fax)
>
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