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
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
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
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. :-)
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