[U-Boot-Users] Re: U-boot i386 port
daniel at omicron.se
Tue Apr 29 16:32:31 CEST 2003
On 2003.04.29 16:12 Tony Chu wrote:
(I am re-adding the U-boot list beacuse this might interest other
people trying to use the i386 port of U-boot).
> I found the reason why my board halt when boot linux:
> our custom Pentium 2 board is based on IBM PC arch.
> so. the address A0000-FFFFF is readonly.
> but u-boot install the realmode interrupt handler at
> F0000. so... actually. the handler can not be copy to
> there. so when excute int xx
> in setup.S, my board halt.
This is really a small BIOS emulator, it lives in shadow RAM at
0xf0000 because it is the space where the BIOS would have been if
we had one.
> I am now wonder this feature(A0000-FFFFF readonly) is
> a problem to boot linux kernel or not???
You should be able to use 0xf0000-0xfffff with any modern chipset,
you only have to use the BIOS shadow feature in the chip-set to map ram
into that region, before you use it. The ability to enable shadow ram
is required in the PCI spec.
> and now, I plan to move the realmod interrupt handler
> to address: 98000(at 90000 + MAX_SETUP_SIZE. any
This area is used by the BIOS for the extended BIOS data area
on a standard PC, the only use that I think linux make of the space is
to read the PS/2 equipment word or something like this. Using this space
for the BIOS emulation code should work unless you want to implement full
BIOS compatability (to boot Windows for example).
More information about the U-Boot