[tulip] tulip and IRQ 0

[Donald Becker]

On Thu, 8 Feb 2001, Nicholas, John S wrote:

> I am running 2.2.15 Yellow dog Linux on an Synergy board (PowerPC).
> With help from Don Becker I got the tulip driver working on my
> system... mostly.

> My problem was with interrupts (as Don pointed out).  I have fixed
> this for 3 of the 4 PMC positions on my board.  In the last position
> the PMC Ethernet board wants to be IRQ 0, but the tulip driver does
> not seem to accept an irq of 0.  I changed the pci-scan.c file line
> 169 as follows and it seems to work:

> [root@dms1 modules]#  diff pci-scan.c pci-scan.c.good
> 169c169
> <                        (pdev->irq == 255)) {
> ---
> >                        (pdev->irq == 0 || pdev->irq == 255)) {
> 
> 
> Is there a reason IRQ 0 can not be used?

On x86 machines IRQ0 means that the IRQ has no mapping.  The original
PCI standard stated that IRQ255 is the correct value, but de facto
practice is that both IRQ0 and IRQ255 mean not-mapped.

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993