Re: HARDWARE: Open-Source-Friendly Graphics Cards -- Viable?

[Stephen Wille Padnos]

Bodo Eggert wrote:

> Geert Uytterhoeven wrote:
>  
>
> > <>On Wed, 20 Oct 2004, Jon Smirl wrote:
>
> > > If you implement VGA you will be able to boot and work in any x86
> > > system without writing any code other than the BIOS.
> > >      
> > Ugh... I prefer _not_ to have VGA compatibility.
> >    
> If you want to be able to see the BIOS, you'll need some legacy emulation,
> but it should be enough to implement MDA output.
>  
Nope.  The PC BIOS looks for "expansion ROMs", and calls initialization 
routines in the ones it finds.  It then expects to be able to call INT 
10 to position the cursor and print text (and read the cursor position, 
what's on screen, etc.).  You could have a BIOS on a network card that 
provides the necessary interrupt routines, but actually talks to a 
remote X server for display functions.  (yes - it might need to 
advertise itself as a video device for this to work)

> Since some VGA cards used to depend on the MDA/CGA BIOS routines, most
> (all?) BIOS variants will implement all nescensary IO functions. You'll
> need some MDA registers for the cursor position (that don't even clash with
> EGA/VGA/CGA), 4K mapped memory at B000:0000 and a loop translating the text.
>  
Right - all video cards provide these BIOS routines (including one the 
one being considered here).  They aren't in the system BIOS.  (Not that 
there are no broken BIOSes around, but strictly speaking, there is no 
need at all for the system BIOS to know anything about the display card 
being used)

- Steve

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