How does IRQ work?

[opuntia]

I have an ASUS a8n-premium and I have an ATI Wonder Elite in PCI slot 2 and an Audigy2 ZS in Slot 3, and a 6800gs in the PCIe.

When I look at the IRQ assignments, it shows the Audigy and the 6800gs sharing the same IRQ. If I move the Audigy to slot2 now the soundcard shares an IRQ with the Marvell Yukon PCI gigabit ethernet controller. Actually is seems like PCI slot2 is always with the marvell and Slot3 is always with the 6800gs.

Is this an issue that they are "sharing" an IRQ, especially with the 6800gs? If so, how do I change the IRQ?

BTW, this was my first build and I found the posts on this forum indispensable in helping me. Thanks to everybody who has ever posted on this forum!

 

[Steve]

Shared IRQs are not a problem, and have not been a problem since we stopped using ISA cards. Any conflict from shared IRQs is the result of bad drivers or buggy hardware.

 

[robtk3]

On my old build, my 9500Pro and my PCI sound card didn't share well together. I simply moved the sound to the next slot up (which assigned a different IRQ). Problem solved. At the time (couple years ago) I read that sound and AGP often don't play nice together. On the other hand, if your rig runs fine...

 

[Jhhnn]

Modern hardware, drivers, and WinXP are designed to share irq's w/o problems. It's actually part of the pci spec, even if some manufacturers were slow to implement it... modern irq's aren't really hardware interrupts, anyway, they're software based, part of the hardware abstraction layer programming.

You can, however, screw things up by installing an ancient pci card that demands its own interrupt...

 

[Peter]

No, IRQs aren't "software based", that's just as bad a myth as the "IRQ sharing" stories.

Having the I/O hardware signal that it's done doing what it's been told to - that is the one essential point about having an IRQ signalling structure in the first place.

The "virtual IRQ" bull came up when people first saw IRQ numbers above 15 - because they couldn't figure (and some still don't) that PCs can actually have more than 15 IRQ lines. Their "explanation" was this must be virtual IRQs. It's not. It's APIC hardware at work.