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

[wes schreiner]

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