[OpenBIOS] sorry to ask this again

Massimo Dentico m.dentico at teseo.it
Wed Apr 5 19:09:30 CEST 2000

Jeff Garzik wrote:
> Massimo Dentico wrote:
> > Jeff Garzik wrote:
> > > Massimo Dentico wrote:
> > > > Sorry for the delay. No distractions this time, only assembly code
> > > > for swithing video modes. ;-) This work, at least for me. Obviously,
> > > > I'm not writing BIOS usually :o) .. so, I don't know if it lacks
> > > > something for functioning as part of firmware.
> > > Thanks for posting code, unfortunately this code does not call the VGA
> > > BIOS to initialize the video card -- this code directly programs the VGA
> > > registers to switch modes, just like vga16fb in the Linux kernel.
> > >
> > > BIOS init must have already executed in order for this code to work.
> > Ops .. an error due to my scarce knowledge of PC hardware
> > and this phrase on the Linux BIOS home page: ".. simple VGA
> > capability up WITHOUT a VGA BIOS ..". So, is there an absolutely
> > necessary initialization phase that precede the setting of a
> > video mode? To switch a video mode requires the setting of dozens
> > of registers .. I hope that the init phase isn't so complicated.
> The init phase is not complicated at all ...

You are right, I had sent the e-mail before read the post of
Matthew Sullivan. It doesn't seem so difficult.

> -- when your computer is booted, one of the first things it does is
> run the video BIOS. The video BIOS is the only place which contains
> the information necessary to set up VGA compatibility.  The video BIOS
> must, for example, program chipset-specific registers before it may
> access framebuffer memory.
> Once all that initialization is complete, you can access the video card
> in one of two ways -- indirectly, by issuing BIOS calls, or directly, by
> programming the VGA and/or extended registers built into the video
> chip.

I know this; the only thing that I have missed, until now, is that
the video card doesn't start directly in VGA compatible mode.

> vesafb in the Linux kernel is an example of using BIOS calls.
> vga16fb is an example of directly programming the VGA registers.
> > Sorry again, my intention was only to help.
> no problem at all... all contributions, especially ones with code
> included, are valuable

Thanks for the patience. :-)

Massimo Dentico
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