[linux-audio-user] audiophile 2496 - spdif in

Robert Jonsson linux-audio-user@music.columbia.edu
Thu Oct 9 13:03:00 2003


Hi,

> >
> >Hi,
> >
> >I'm pretty sure I've read that APIC is a no no and should be avoided.
>
> I'd like to see what you read.  In my experience it either works or it
> doesn't.  One can't avoid using APIC interrupts in a dual-processor
> system.

I may be barking up the wrong tree about APIC, there are other acronyms that 
may be at work here ;)....

But, to conclude, I think the source of my argument is probably here on the 
list. If memory serves me it was Mark Knecht (who also had written the text 
on the page below) that had commented about it earlier...

The reasoning (i think) was that IRQ priority and IRQ sharing are the two 
important things to look out for. With APIC you get enough IRQ's, but you 
don't know which priority they have to each other which is fatal.

> >Here's a link to some interesting info about "normal" IRQs in a PC. There
> > is more to it than just having an "OWN" IRQ, they have different
> > priorities.
> >
> >http://myweb.cableone.net/eviltwin69/Arcana.html#IRQs
> >
> >See also (the source)
> >http://www.djcj.org/LAU/guide/Low_latency-Mini-HOWTO.php3
> >
> >
> >/Robert
>
> Yes, that HOWTO has good info, as far as it goes.  One thing I would add
> though, is that when using non-APIC interrupts the interrupt priority is
> not fixed in stone (or silicon, as it were).  Using the program
> "irqtune" one can change interrupt priorities (see
> http://www.best.com/~cae/irqtune ).  I havn't used irqtune in a while,

Cool! I didn't know it was possible to device such a program. Have to check it 
out!

/Robert

> not since kernel 2.2 days, so I'm not altogether sure that it works
> correctly with 2.4.x kernels.  On Debian it is in the "hwtools"
> package.  Hmm, I just tried it on a box with a 2.4.21+lowlatency kernel
> and it seems that it worked, though it gave some warnings.  I can't
> really test if the IRQ priorities have changed though.   YMMV.
>
> wes