Why do PPC PCI cards need Mac-specific bios/firmware?

[boojummy]

Hi Everyone,

My apologies if this is OT; this forum seemed more appropriate than OtW, since PPC folks actually read this one...

Anyhow, my question is a general question about Mac hardware: why do add-on cards, i.e., PCI cards, require "Mac firmware"? I was once told in a forum that I could, for example, use an ATI Radeon card (manufactured for a PC) in a Linux/PPC setup, with the one gotcha that no video would be displayed until the kernel loaded the appropriate driver.

So what makes Mac hardware special in this regard? Is this related to Open Firmware?

To give you some background, here's something I'm working on. At work, we ordered an Adaptec PowerDomain 2930 (PCI-to-Ultra SCSI adapter). Unfortunately, we were accidentally shipped an Adaptec 2930CU, which, except for the "Mac BIOS", is an identical card. MacOS X will not recognize this card at all, and Adaptec's knowledgebase only briefly mentions that this card is not Mac-compatible. I have not tried this in a Gentoo box yet; I will try it in my PPC setup at home later. Anyhow, that's what prompted my question.

Can anyone enlighten me as to why this is the case?

Thanks,
-b

[ozonator]

As far as I know, Mac firmware is needed so that the device can be used before an OS loads. I suspect this is related to Open Firmware, since OF is handling the boot process. To see something on your screen before an OS loads its video drivers, the video card has to be recognized by OF; to boot from a drive on a SCSI card, the SCSI card has to be recognized by OF. Having firmware in a card that matches the host hardware is typically a good thing: most users expect their video cards to show the boot process, their disks to be bootable, etc.

But, if you don't need the card to function at boot, i.e., before the OS kernel and drivers load, it doesn't need Mac firmware, provided the OS ultimately has drivers for it (e.g., I use generic PCI network and USB cards in my PowerMac, both of which work nicely while running Linux). It's only if they provide something needed at boot time that a specific Mac version with Mac-compatible firmware is needed.

Of course, this is the explanation I thought of a while ago (it struck me the first time I saw a controller card load its BIOS on a PC before an OS booted), and it makes sense to me. Nevertheless, a true expert on such things should feel free to correct me if I'm wrong.

[fishhead]

Yep, ozonator is more or less on the money. OpenFirmware (used by Sun and Apple) uses a sort of interpreted Forth (a computer language) thus making it, in theory, platform independant (although I've never tried transplanting between a Sun and an Apple). In general, if the machine doesn't try to read the device's BIOS, you'll be fine. I heard from someone that OpenFirmware might be coming to the PC world soon (and it would be cool if it did) but don't hold me to it