[PlanetCCRMA] hi fedoritas gurus!

Luis Garrido luisgarrido at users.sourceforge.net
Sun Aug 9 15:16:31 PDT 2009

>> else of intel device, is there any way to assign to the firewire a
>> different IRQ that from the BIOS? I'm working with a Macbook pro,


First of all, I'd recommend you to use in the future a more explicit
subject for your message related to its contents, something like
"Changing firewire IRQ".

On with your question.

I don't know about Macbook's, but in most laptops IRQs are hardwired,
so there's nothing you can do to change them.

Anyway, fiddling with interrupts is complicated. What's the problem
you are trying to solve? Are you sure your USB devices are interfering
with your firewire one?

If your audio interface suffers from the competition of other devices
wired to the same IRQ there are two possible solutions:

1) Disable those devices unloading their kernel module.

For instance:

# cat /proc/interrupts | grep 1394
 22:          1   IO-APIC-fasteoi   ohci1394, Intel ICH6 Modem

In my laptop the firewire port shares IRQ 22 with the built-in
software modem. In the unlikely case that an inactive modem stole
enough IRQ-handling CPU time to cause xruns I could simply unload its
controlling kernel module:

# rmmod snd_intel8x0m
# cat /proc/interrupts | grep 1394
 22:          1   IO-APIC-fasteoi   ohci1394

(coolly blows the smoke out of the barrel of his six-shooter)

2) Apparently 2.6.31 kernels allow you to prioritize IRQ handlers even
if they are triggered by the same IRQ, so I could raise the priority
of the firewire handler and lower the modem's one. This is somehow a
new feature that I haven't tested personally, but I have read some
discussion about it on the LAD list.

Hope this helps,


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