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Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios

From: Kevin O'Connor
Subject: Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios
Date: Thu, 26 Nov 2009 02:15:27 -0500
User-agent: Mutt/1.5.19 (2009-01-05)

On Thu, Nov 26, 2009 at 08:49:25AM +0200, Gleb Natapov wrote:
> On Wed, Nov 25, 2009 at 05:53:49PM -0500, Kevin O'Connor wrote:
> > * If qemu does reload the bios (a hard-reset) then there is a good
> >   chance that old DOS programs will break when they invoke a reset in
> >   an attempt to switch from protected mode to real mode.
> > 
> > Is that correct?
> > 
> Reloading of a BIOS will not prevent old DOS program from working.
> It will slow switch to real mode, but otherwise I see no harm. What may
> prevent them from working is the fact that too much devices are reset on
> triple fault, but this has nothing to do with reloading of a BIOS.

On a switch to real mode, seabios will detect the code in cmos and
jump directly to the resume vector.  Seabios will not reinitialize
itself in this case.

Now, if the bios is reloaded, the jump to the resume vector will skip
ide, bios table, and other internal state setup.  So, later calls to
the bios will likely fail.


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