Re: IRQ clash

[John Jordan <junk@xxxxxxxxxxxx>]

A. J. Moss wrote:
> A few frustrating hours spent searching for a hardware fault ended
> when I moved a RAID card from PCI slot 4 to slot 3, to stop its IRQ
> clashing with my USB keyboard.
>
> Does PCI-X assign IRQs to slots in a less inflexible way than PCI?

I'm pretty sure it's the same. A PCI bus has four IRQ lines (usually 
termed A-D) which are hardwired to slots. Each of these is then mapped 
to one of the PIC IRQ lines, which are frequently shared with other 
devices in modern PCs.

The usual process for shared IRQs is that when the driver's IRQ handler 
is called, it first asks its device whether it triggered the IRQ. If 
not, it hands control to the next driver in the chain. As a result, IRQ 
clashes should only be a problem for modern OSs if a driver is very 
badly written.


--
John Jordan