[U-Boot-Users] Re: U-boot i386 port

Daniel =?gb2312?Q?Engstr=F6m?= 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
> problem???
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).


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