[Open-graphics] From PCI to VGA registers

[Timothy Normand Miller]

On 9/5/07, Mark <mark at jarvin.net> wrote:
> Anton Soppelsa wrote:
> >> > * From the discussion going on here, it looks like initialising the
> >> > video card is not straightforward at all. Is a PCI VGA card more
> >> > difficult to set up that any other types of PCI cards?
> >>
> > It's totally straightforward, if you have proper documentation.  The
> > VGA BIOS, also, is just code in ROM that the CPU executes.  It is
> > called from the system BIOS at an appropriate time.  VGA is only made
> > complex by the fact that PC BIOS and software assume certain specific
> > capabilities of the graphics card.
> >
> Does the PC BIOS expect anything *besides* 80x25 text mode?  What's the
> minimal set of expectations the PC BIOS has of the graphics card?

If I boot DOS, what I have seen with some BIOSs is that the system
comes up in 640x350 mode, 80x25 with 8x14 font.  Then it switches to
640x400 (8x16 font) and stays there.

> Let me guess: it's not standard, right? ;)  I'm thinking of PC BIOSes
> that give a splash screen during POST, for instance.

I last experimented with a VGA BIOS when most PCs didn't have an
interesting splash screen.  So I have no idea what they're doing
there.

> What's a reasonable minimum, then?

No idea.  I think we should do a set of standard modes and then fix
problems as they come along.  If we can do 640x480x16 planar, then
there's no reason we can't also do 320x200x2 packed.

-- 
Timothy Normand Miller
http://www.cse.ohio-state.edu/~millerti
Open Graphics Project