Re: [Linux-fbdev-devel] Reading the EDID block for x86 machines

[Jon S. <jon...@ya...>]

The VBIOS should be position independent code and it
will run at any 64K boundary. The PC bus spec simply
says the video BIOS defaults to C000, it is not a
requirement that it be located there. For example if
you look at the aty128fb driver's find ROM routine
your will notice that it is searching a broad address
space for the ROM.

I'm still not convinced that the memory at C000 is
really hardware write protected, I think it is just
RAM with a copy of the ROM in it. For example if I
turn off BIOS shadowing my system will not boot. When
debugging this I spent some time tracing into the ATI
ROM and I was pretty sure that they are dependent on
begin copied into RAM before begin run. 

Do you have a DOS floppy around? Just boot into DOS,
start debug and see if you can change C000:0.

If C000:0 is hardware write protected, there is
nothing stopping the ROM from begin copied into 8000:0
or 9000:0 or whatever where there is guaranteed RAM.
We would just need to temporarily get the kernel out
of the way.

=====
Jon Smirl
jon...@ya...

__________________________________________________
Do you Yahoo!?
Yahoo! Platinum - Watch CBS' NCAA March Madness, live on your desktop!
http://platinum.yahoo.com