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New text modes on SiS chipsets, info / docs wanted (Miscellaneous)

posted by Ninho(R) E-mail, 20.03.2009, 13:18

> > I avoid SiS chips at all, because these are slow and crappy.
>
> I agree. I have one SIS 6xxx PCI VGA that I bought because I need TV-out
> on a PCI. It was cheap but it is crap.
>
> I cannot tell you anything to SIS but just idea how it works on nVidia
> BIOS.

It won't tell me anything about the SiS registers : programming any 'superVGA' chipset requires a knowlege of the purpose of every bit in every register (and access to features which were not part of IBM's original VGA is generally protected by 'password'!) Failing an authoritative documentation, the next best thing would be to look at video BIOS or other code made by ppl who had access to the docs. Unfortunately their is nothing in the video BIOS for my Asrock board that tells me how to program the divisors for and activate extra frequency generators. But of course it has to be possible in principle, just that SiS (and others) have lost any interest in text modes because their customers don't care about DOS nor compatibility any more.

I've had some experience in playing with video chipsets : back in the 80s, I managed to enhance a Goupil AT clone having a Paradise EGA system on the mainboard (and a good, 13"! EGA multisync monitor, possibly of Sony design, not your basic crappy EGA) and in particular I forged 126 characters wide text modes; it was fun (not) because if you'll remember, with EGA you couldn't read back the registers at all...and I almost became blind in the process ;=) I had to define a set of six-bit-wide characters, but the real difficulty was finding the hidden registers, password, and how to tweak the whole stuff.

> nVidia has defined some internal gfx and txt mode numbers that are
> supported by chip. Then there is a table that assigns VESA mode numbers to
> specific nVidia mode numbers.

That step is really the last piece of icing, we need to fabricate the modes, and only then optionaly give them BIOS and/or VESA 'int 10' numbers. I prefer to keep the BIOS mode as 03 for tesxt color modes of any width, and of course update the mode's params in BIOS data segment 40h. They are for use in DOS anyway, not Windows.

---
Ninho

 

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