[OpenBIOS] Video

[Jeff Garzik]

"Ronald G. Minnich" wrote:
> My question to you: if I enable the address/IO bits to enable 'VGA', and
> then I do VGA-style commands to the card, will the card initialize or sit
> there and do nothing?
> 
> Is there really no way short of calling the video bios to init the card?

Each video card has a _lot_ of knowledge stored in the video BIOS.

When a card is made, an OEM takes a video chip and sticks it on their
board.  The only way for the chip to know how to correctly access board
memory, and other crucial details, are stored in the video BIOS.

The rule is:  if you do not init video BIOS, then you must init the
video on a per-chipset basis (ie. no generic VGA)


> Next question then: what's the offset in video bios of the init routine,
> or how do you find it, and what's it expect? working stack? return address
> in bx? Does it walk the PCI bus to find itself, and then init itself? what
> should I expect?

Read the PCI spec on ROMs.  Basically it can be an x86 code image, Open
Firmware code image, or something else.

You will always have the problem of having to deal with x86 code images
in expansion ROMs.  Video BIOS is only one example.

-- 
Jeff Garzik         | The ultimate Windows 98 keyboard:
Building 1024       | Ctrl, Alt + Del on one big key!
MandrakeSoft, Inc.  | 	- another cute fortune
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