Subject: Re: Another changer, another changer problem
To: David Maxwell <>
From: Bill Studenmund <>
List: current-users
Date: 10/05/1998 14:02:57
On Mon, 5 Oct 1998, David Maxwell wrote:

> > No one's mentioned it, but you can.
> > 
> > ahc1    at pci0 dev 12 function <whatever>
> > ahc2    at pci0 dev 13 function <whatever>
> I have a feeling that certain BIOS' (What the plural of BIOS? BIOSae?) may
> not keep these constant, or for that matter that different BIOS sets will
> pick the same numbers if you swap a motherboard. I also don't know how to
> find these numbers out except by booting multiple times and adding one
> card each reboot.

Actually, the "dev" number is motherboard-specific. It's a function of how
the motherboard (well, the host-PCI chipset) deals with configuration
space writes and how the board is wired. When you access a configuration
register, part of the address is decoded using a wire which is fed
directly to the chip/card.

So if you know a particular motherbaord, you can tell what card is in what
slot according to the pci device number. You probably can even get that
info from the vendor.

It's BIOS-independent.

Though the only way I know at present to find out what's what is to do a
boot and look at the output. Though if you had three different PCI cards,
you could boot w/ each one of them in, and get all the #'s at once.

Take care,