On 7/13/06, sudheer <urwithsudheer@gmail.com> wrote:
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> Anyone please help me if i am missing anything.
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>     All PCI VGA cards for use on x86 PCs have a ROMscan BIOS
extension on them. This initializes the card after POST - basically,
the motherboard BIOS transfers control to the BIOS on the
PCI VGA card, which then initializes itself. If control is not
transfered to the VGA BIOS on the card, the VGA controller
stays isolated and will not respond to PCI device enumeration,
etc. This is actually part of the PC-98 spec., which allows
multiple VGA controllers to co-exist on the PCI and/or AGP
bus.

   On a PowerPC system, the ROMscan BIOS cannot execute
(because it has x86 instructions in it), so there will be an alternate
way to initialize the VGA controller so that it can respond to the
PCI enumeration, etc. However, that method will be card/controller
specific - neither the card manufacturer nor ATI may ever have
released the specs for how this is done. Usually, it will be through
hidden memory-mapped IO (MMIO) registers on the VGA controller
chip, but there are numerous proprietary ways to implement this,
most of it being undocumented or controller-specific.

(Lots of things are taken for granted in the x86 PC world, which
are actually very complex and difficult-to-implement protocols.
That's one of the reasons why all the alternative PC processor
architectures have failed over the last 20 years).

-Siva