From: Jamie Lokier <jamie@shareable.org>
To: Jos Hulzink <josh@stack.nl>
Cc: Linus Torvalds <torvalds@transmeta.com>, Andi Kleen <ak@muc.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Use correct x86 reboot vector
Date: Sun, 11 May 2003 15:01:44 +0100 [thread overview]
Message-ID: <20030511140144.GA5602@mail.jlokier.co.uk> (raw)
In-Reply-To: <200305111137.29743.josh@stack.nl>
Jos Hulzink wrote:
> On Sunday 11 May 2003 05:50, Linus Torvalds wrote:
> > 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.
I got my info from an article on the net which says that a 386 does
behave as you say, but it is possible for the system designer to
arrange that it boots into the 286-compatible vector at physical
address 0x000ffff0. It states that the feature is specifically so
that system designers don't have to create a "memory hole" (that's as
much detail as it gives).
I can't be arsed to look in a real 386 manual though :)
> 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...
You can set up unreal mode but it is quite fiddly.
-- Jamie
next prev parent reply other threads:[~2003-05-11 13:49 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-10 2:56 [PATCH] Use correct x86 reboot vector Andi Kleen
2003-05-10 3:35 ` CaT
2003-05-10 3:58 ` H. Peter Anvin
2003-05-10 14:49 ` Alan Cox
2003-05-10 16:17 ` Jamie Lokier
2003-05-10 18:47 ` Jos Hulzink
2003-05-11 18:01 ` Eric W. Biederman
2003-05-11 17:24 ` Alan Cox
2003-05-11 19:04 ` Eric W. Biederman
2003-05-12 5:48 ` [PATCH] always shutdown on the bootstrap processor Eric W. Biederman
2003-05-10 16:15 ` [PATCH] Use correct x86 reboot vector Jamie Lokier
2003-05-10 17:09 ` Randy.Dunlap
2003-05-10 19:41 ` Jos Hulzink
2003-05-10 18:10 ` Jamie Lokier
2003-05-10 20:55 ` Jos Hulzink
2003-05-11 3:50 ` Linus Torvalds
2003-05-11 9:37 ` Jos Hulzink
2003-05-11 14:01 ` Jamie Lokier [this message]
2003-05-11 17:38 ` Davide Libenzi
2003-05-11 17:56 ` Eric W. Biederman
2003-05-11 18:23 ` Davide Libenzi
2003-05-11 19:12 ` Eric W. Biederman
2003-05-12 15:36 ` Maciej W. Rozycki
2003-05-13 6:35 ` H. Peter Anvin
2003-05-11 18:38 ` Linus Torvalds
2003-05-11 19:00 ` Matt Mackall
2003-05-11 19:16 ` Eric W. Biederman
2003-05-12 1:07 ` H. Peter Anvin
2003-05-11 19:10 ` Eric W. Biederman
2003-05-11 18:43 ` Christer Weinigel
2003-05-11 20:22 ` wingel
2003-05-11 20:26 ` Davide Libenzi
2003-05-11 17:54 ` Eric W. Biederman
2003-05-13 12:49 Chuck Ebbert
2003-05-13 18:45 ` H. Peter Anvin
2003-05-13 19:04 ` Richard B. Johnson
2003-05-13 19:27 ` H. Peter Anvin
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