Initialising 2nd VGA card

[Herman]

Hello,

I try to iniitilalise a 2nd VGA card on an Intel x86 PC with PCI vs 2.

If i use 2 of the same cards I can initialise calling C000:0003. But using a different card i don't know how to load the VGA Bios of the second card.
I downloaded the asm-code in a Dos environment.
Now I try to do it in Dos, just to know how it works.
Or does anyone have another suggestions?

[Pype.Clicker]

afaik, VGA allows for one colour and one monochrome card to be present together (because they use different ports mapping). But for 2 full-featured VGA cards, well ... i don't know too much how it would work.

The BIOS memory could certainly be found by scanning the PCI resources of the card, and maybe you could configure the second card this way, but nothing certain ...

btw, once you'll get the BIOS of the hidden card, what guarantees it will work in such conditions ?

Just a derivated question i wonder : how can a PCI card emulate the ol' good behaviour of VGA-ISA cards ? i bet i should go back in PCI description books ...

[tom1000000]

Hi,

I'm no expert but I am 90% certain that standard VGA only supports ONE video card.

To get 2 video cards working, you have to write native drivers similar to the windows / linux variety.

As for how does PCI VGA emulate ISA VGA??? I thought VGA was entirely managed through the IO ports, so there's no need to worry about the actual bus its on (at least from a software persepective)?

[RicoSanchez]

Yeah, iirc standard VGA only supports one video card.

And yes, VGA is entirely managed through the IO ports. New videocards have to implement that to be backward compatible with VGA, just like for modern keyboards (usb keyboards), they also implement backward compatibility for PS/2 (well, the keyboard doesn't, the keyboard controller on the motherboard does).

[Tim]

It's technically possible to have multiple PCI/AGP cards in one system. AFAIK it's possible to access them independently if the BIOS or OS assigns the I/O port and memory ranges separately. That is, you'd have one primary card whose frame buffer was at A0000 and whose ports were in the normal place, and a secondary card with a frame buffer and ports somewhere else. You could access the primary card through the BIOS, but you'd have to access the secondard card directly (unless you swapped the base addresses over).

By way of experiment, try plugging two PCI cards, or a PCI and an AGP card, into one machine, and seeing what resources the OS assigns (e.g. Device Manager in Windows).