[Milkymist-devel] IRQ handling code

[Michael Walle]

Am Thursday 18 March 2010 14:07:26 schrieben Sie:
> Hi,
>
> On Wednesday 17 March 2010 00:15:48 Michael Walle wrote:
> > Am Tuesday 16 March 2010 15:53:41 schrieb Sébastien Bourdeauducq:
> > > Therefore, it gets ALL interrupts (masked or not). We should AND
> > > register IP with register IM.
> >
> > yep. imho that should be done within the asm code.
>
> Yes, but this requires extra asm instructions that no longer fit between
> two LM32 exception vectors and therefore a jump is needed. I wanted to
> avoid it, that's why I did it this way. But since it is inconsistent with
> other Linux ports, I will change it.
>
> > other linux ports pass only one single irq number to do_IRQ().
> >
> > What about the following steps:
> >   1. interrupt vector gets called
> >   2. save regs
> >   3. r2 <- IM & IP
> >   4. find position of first bit set in r2, store it in r1
> >  (4a. r2 <- pt_regs)
> >   5. mask irq
> >   6. call do_IRQ (which only takes one irq number)
> >   7. ack irq
> >   8. unmask irq
> >   9. restore regs
> >  10. eret
> >
> > Processing only one interrupt at a time should avoid the second problem,
> > mentioned above.
>
> Sounds good. It takes more CPU cycles to achieve the same thing when
> interrupts come at the same time, but since I guess this rarely happens,
> the small performance improvement is not worth the cost of doing
> differently than other Linux ports.

see attachment

-- 
wkr michael
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