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SubjectRe: AMI winBIOS: does it matter ?
On Wed, Nov 25, 1998 at 02:52:44PM -0500, Paul Barton-Davis wrote:
> I'm about to buy a dual Slot 1 motherboard.
>
> Tom's Hardware notes of the Supermicro P6DBS mother board:
>
> board shows interesting phenomenon. WinBIOS would not let you disable
> USB properly, which grabs IRQ9. To use this IRQ you have to plug the
> PCI card into PCI Slot 4 (the one next to the AGP Slot), PCI Slots 1
> and 2 will only get IRQ11, which is already used by AGP VGA and it
> leads to crashes with several AGP cards if this IRQ is shared. Hence
> the network card needs to be plugged into PCI 4 to get the last free
> IRQ (IRQ9), whilst the onboard SCSI adapter always grabs IRQ10,
> otherwise the system will not run with e.g. a RIVA card. To make this
> all work you will have to disable the USB manually in the Windows 95
> system manager. This board shows a very inflexible way of distributing
> IRQs over the 4 PCI slots, which cannot be improved by any BIOS
> setting. If you are using an AGP card and need the EIDE ports as well
> as both COM ports and the printer port, you can *only* use PCI Slot 4
> for *one* card that needs its own IRQ.
>
> My impression is that for Linux, the BIOS is essentially irrelevant,
> and Linux will do whatever it wants. But reading the above, its not
> totally clear to me that this is true.
>
> Can anyone explain if it matters ?

On a UP system, Linux will normally use the IRQs assigned from the BIOS, so
it does matter. However, Linux does allow IRQ sharing without problems,
normally. And you don't use VGA interrupts in Linux.
On an SMP machine, the PCI IRQs will be routed through the IO-APICs by Linux
and thus be reassigned. I think, Linux uses some BIOS' information (MP-table?)
for that, but I don't understand this mechanism exactly.

FYI: I recently bought a DFI P2XBL/D (Dual BX withOUT SCSI). It has Award
BIOS and caused no problems since I disabled APM in the BIOS.

--
Kurt Garloff <K.Garloff@ping.de> (Dortmund, FRG)
PGP key on http://student.physik.uni-dortmund.de/homepages/garloff

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