Subject: Re: [linux-audio-user] audiophile 2496 - spdif in
From: wes schreiner (wes_AT_infosink.com)
Date: Thu Oct 09 2003 - 15:49:02 EEST
Robert Jonsson wrote:
>Thursday 09 October 2003 12.26 skrev wes schreiner:
>
>
>>jordan muscott wrote:
>>
>>
>>>Ok to be honest I'm not gonna switch distros...... but are you saying
>>>that Redhat offers you extra software that allows you to change the
>>>IRQs that your pci cards are on?
>>>
>>>
>>There is no such software on any distro. Your motherboard's BIOS decides
>>which PCI slots get which IRQs. In a few motherboards the BIOS lets one
>>select which IRQs get assigned to certain slots, but most don't. So with
>>most motherboards all one can do is move cards around to different slots
>>and then see what IRQ gets assigned. If your sound card and your
>>ethernet card are sharing an IRQ, that's because those PCI slots used
>>both have the same IRQ assignment. If you swap just those two cards
>>slot-for-slot they will end up with the same IRQ again. Try moving just
>>one of the cards to another slot. If all of your slots are full then
>>move multiple cards.
>>
>>On some motherboards with some processors you can turn on Local APIC
>>support in your kernel config and get more IRQs to work with. Dual
>>processor motherboards, even if they have only one CPU installed, can do
>>this to get more IRQs. If you have dual CPUs you should already be
>>running a SMP kernel and you probably don't have IRQ assignment
>>problems. If you do, it's back to juggling cards.
>>
>>wes
>>
>>
>
>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.
>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,
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
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