Timothy Normand Miller wrote:
On Fri, Aug 1, 2008 at 3:25 PM, Mark Marshall
<[EMAIL PROTECTED]> wrote:
Another question with this sort of setup is to do with the motherboard
copying the VGA BIOS from ROM into RAM and calling the initialization
function - does this happen for each VGA separately? What does it do with
the memory from the first when it calls the second?
I'm not sure where this sort of stuff is specified, any ideas?
Somehow, I had gotten the impression that the VGA BIOS goes in a fixed
location in the lower 1 meg, and that only the BIOS from the main
console gets shadowed there. Other VGA cards are treated like generic
PCI devices, having their BARs assigned space (if that's enabled in
the BIOS config), but with memory space decode disabled, and the PROM
is pretty-much ignored.
This is explained in section 6.3 of the PCI spec.
<< quote from the PCI spec (this is version 2.3, 6.3.3.1.1) >>
1. Map and enable the expansion ROM to an unoccupied area of the memory
address
space.
2. Find the proper image in the ROM and copy it from ROM into the
compatibility area
of RAM (typically 0C0000h to 0E0000h) using the number of bytes specified by
Initialization Size.
3. Disable the Expansion ROM Base Address register.
4. Leave the RAM area writable and call the INIT function.
5. Use the byte at offset 02h (which may have been modified) to
determine how much
memory is used at runtime.
Before system boot, the POST code must make the RAM area containing
expansion
ROM code read-only.
POST code must handle VGA devices with expansion ROMs in a special way. The
VGA device’s expansion BIOS must be copied to 0C0000h. VGA devices can be
identified by examining the Class Code field in the device’s
Configuration Space.
<< end quote >>
Tom's entry to the Glossary page describes what happens in the
multi-card case; one gets picked and the others get ignored.
MM
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