From owner-freebsd-hackers  Thu Dec  6  9:35:29 2001
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From: Nate Williams <nate@yogotech.com>
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Date: Thu, 6 Dec 2001 10:35:19 -0700
To: John Baldwin <jhb@FreeBSD.ORG>
Cc: Nate Williams <nate@yogotech.com>, freebsd-hackers@FreeBSD.ORG,
	Ronald G Minnich <rminnich@lanl.gov>
Subject: Re: Re[2]: switching to real mode
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> >> > I saw an example of switching in real mode in linux' sources (it looks
> >> > pretty clear) and thouhgt it is possible to do the same under FreeBSD.
> >> > The problem is I'm absolutely lost in FreeBSD's physical memory management
> >> > implementation (page tables and directory and so on).
> >> 
> >> That code is quite broken. You need to check out the ones I mentioned
> >> earlier. All that the code does in the linux kernel is fail badly.
> >> 
> >> Actually there used to be in freebsd some really nice code for popping
> >> into real mode and back again. It was to support calling BIOS for certain
> >> things.
> > 
> > I believe the code is still there, and it's used for APM bios calls,
> > if I remember correctly.
> 
> It uses VM86 mode, not real mode.  Going back and forth to real mode is too
> expensive.

Ahh, that's right.  However, if I remember right, in older versions of
FreeBSD it did the real-mode switch, because we didn't have the VM86
code.

(This would be prior to FreeBSD 4).


Nate

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