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SubjectRe: [PATCH] Use correct x86 reboot vector
On Sunday 11 May 2003 05:50, Linus Torvalds wrote:
> On Sat, 10 May 2003, Jamie Lokier wrote:
> > Jos Hulzink wrote:
> > > For the sake of bad behaving BIOSes however, I'd vote for the f000:fff0
> > > vector, unless someone can hand me a paper that says it is wrong.
> >
> > I agree, for the simple reason that it is what the chip does on a
> > hardware reset signal.
> Hmm.. Doesnt' a _real_ hardware reset actually use a magic segment that
> isn't even really true real mode? I have this memory that the reset value
> for a i386 has CS=0xf000, but the shadow base register actually contains
> 0xffff0000. In other words, the CPU actually starts up in "unreal" mode,
> and will fetch the first instruction from physical address 0xfffffff0.
> At least that was true on an original 386. It's something that could
> easily have changed since.
> In other words, you're all wrong. Nyaah, nyaah.
> Linus

Source: 80386 Programmers Reference Manual, Intel (1986)

EIP is set 0000FFF0H
CS is set F000H

After RESET, lines A31-A20 are FORCED high till a far JMP is done.

So, unfortunately we have to say Linus is right once again. Damn ;-) My
conclusion is that we are unable to use the CPU reset as the reference for
warm boots, for we can't control A312-A20 in real mode. But as far as I can
see, my arguments still hold...

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