PCI interrupts and how they work

[Kerry Hoath]

You are correct. A PCI card can request 1 2 3 or 4 irqs
called INT A Int B Int C and Int D.
If you request Int D you get 4 interrupts which may or may not
be level triggered and may or may not be sharable. If you are running
a PCI 2.1 BIOS and set plug 'n' play OS to no,
Linux can share interrupts The system maps pci int pins to motherboard
irqs and if the os is in protected mode they can be level triggered.
You can't share interrupts under dos because the code is not re-enterant.
Linux does however have correctly coded handlers so given the right hardware bios settings etc
it can share irqs. Windows doesn't usually let a soundcard share
an IRQ since many cards must retain some sort of dos sound bastard compatability
for games.

Regards, Kerry
On Tue, Mar 05, 2002 at 10:12:17PM -0600, Kirk Wood wrote:
> The IRQ is not coded into the modem. It is however often beyond the scope
> of Windows to change it. There is an interplay between the card and the
> motherboard. Many PCI cards are designed to only work on the IRQ assigned
> automatically by the motherboard. If you really want to change it, do one
> of two things. Move the modem to another slot. Change the BIOS settings on
> IRQ assignment order for PCI slots.
> 
> =======
> Kirk Wood
> Cpt.Kirk at 1tree.net
> 
> Nowlan's Theory:
>         He who hesitates is not only lost, but several miles from
>         the next freeway exit.
> 
> 
> 
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-- 
Kerry Hoath:  kerry at gotss.net kerry at gotss.eu.org or  kerry at gotss.spice.net.au