[Open-graphics] From PCI to VGA registers
paul at codesourcery.com
Wed Sep 5 12:28:27 EDT 2007
On Wednesday 05 September 2007, Dieter wrote:
> > In order to facilitate early boot access to a device some cards have a
> > chunk of ROM BIOS code on them. Typically this will be x86/pc machine
> > code and/or Forth OpenFirmware code. If you can't run this natively you
> > have to either emulate it (Xfree86 contains an x86 emulator for this
> > purpose), or just build the setup code into your system and ignore the
> > rom.
> It is not clear to me how Xfree86 having an x86 emulator helps with early
It doesn't, but it allows you to get the hardware going once the OS has
booted. This is mainly to workaround proprietary hardware where the cold
startup sequence is not known, you have to blindly run the BIOS code.
For OGA we have full hardware docs so this is not really an issue. The OS
driver (or firmware) can bring the card up itself.
> > For non-x86 systems we generally don't care about vga compatibility.
> How does the non-x86 firmware display console messages?
Short answer is that it doesn't.
Long answer is that AFAIK the PC is the only vaguely recent (within the last
last 15ish years) machine that uses text display modes. Other systems either
have "native" drivers for the hardware (maybe implemented in Forth) to
provides a graphical framebuffer, or use a serial/ethernet port.
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