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As you have put

Hi List,
Actually I have the same question for a long time, i.e. could someone
explain a little more about the delay slot to me? Becasue there 's too
few explainations I can find from openrisc documents.

As far as I know, all the the "l.jump" instructions will be followed
one delay slot. The instructions stored in the delay slot will be
performed beform the "l.jump". Do I understand correctly? If so, why
do we have to design such a delay slot? what is it used for? why the
l.jump have to performed after the instructions in the delay slot? And
in the program I 've seen, more then 90% "l.jump" is followed by a
"l.nop", so is the delay slot really necessary, why not combine the
two together?

I know this perhaps because of the pipeline of openrisc, but again,
there's no more description for pipeline in the document. Thanks a lot
for help.

/Xiang

On Tue, Jul 8, 2008 at 9:23 AM, Robert Cragie <rcc@j...> wrote:
> As you have put
>
>     l.jalr     r2
>     l.addi    r2,r0,0
>
> then as far as I can see it you have set r2 to 0 in the delay slot, which
> will be executed before the jump. Therefore you will be jumping to 0. Try:
>
>     l.jalr     r2
>     l.nop
>     l.addi    r2,r0,0
>
> Also, maybe think about saving r2 on the stack in the ISR instead of just
> clearing it.
>
> Robert
>
> silzon@n... wrote:
>
> Hello. I run or1200 RISC on Evaulation board.
> I am programming GPIO interrupt system.
> It work interrupt service routine, but,
> After interrupt service routing is finished, It doen't return back!
> my reset.S is..
> .org 0x800
> _hpint:
>     l.movhi  r2,hi(_isr_gpio)
>     l.ori      r2,r2,lo(_isr_gpio)
>     l.jalr     r2
>     l.addi    r2,r0,0
>     l.rfe
>
>
> what's wrong??
>
>
> please, help me :)
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>
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> Direct: +44 (0) 114 281 4512
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