VGA routing

VGA routing

[Jon Smirl]

My machine has three busses.
1) on chip
2) AGP
3) PCI

My primary display is on a PCI card.
When I boot the VGA ports are routed through the PCI bridge.
I'm running X on the PCI card.

Now I load a device driver that enables the AGP card. After doing this the VGA
ports are routed to the AGP bus. Where does this happen?

Now if I do a VT switch the VGA ports get routed back to the PCI bridge. Where
does this happen?

Thanks for the help. I'm trying to figure out the right way to initialize a
secondary card by jumping to C000:0003 in it's BIOS. Does Xfree jump to
C000:0003? I can't find where it does that in the source.



=====
Jon Smirl
jonsmirl@yahoo.com

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Re: VGA routing

[Matan Ziv-Av]

On Sat, 6 Dec 2003, Jon Smirl wrote:

> My machine has three busses.
> 1) on chip
> 2) AGP
> 3) PCI
> 
> My primary display is on a PCI card.
> When I boot the VGA ports are routed through the PCI bridge.
> I'm running X on the PCI card.

There is VGA bit of Bridge Control register in PCI-PCI bridges (bit 19, 
at 3c). But when there are a few cards on the same bus, I guess the 
behaviour is undefined, since I did not see anything relevant in the 
standards. 

> Thanks for the help. I'm trying to figure out the right way to initialize a
> secondary card by jumping to C000:0003 in it's BIOS. Does Xfree jump to
> C000:0003? I can't find where it does that in the source.

x86emu package does this by disabling all cards except for the one that 
is being initialized.


-- 
Matan Ziv-Av.                         matan@svgalib.org



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