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

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

The system BIOS may not map the ROM into the first 1MB
to copy it. It probably maps it to a high address and
then plays with the X86 memory management to map a
segment register to it. I am having vague
recollections about doing this long ago when I worked
at MS.

I seem to recall there is a real mode instruction that
will force a register like ES to point to a high mode
address.  This is how an ancient EMM driver (remember
the AboveBoard and Lotus 123?) was implemented on a
386 without special hardware.

So you would map the ROM to a high address, map the
segment register to it, copy to C000, restore segment
register and jump to C000:3.

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

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