From owner-freebsd-hackers  Sat Nov 16 17:45:48 1996
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To: Erich Boleyn <erich@uruk.org>
cc: hackers@FreeBSD.org
Subject: Re: Memory probe(s) in FreeBSD 
In-reply-to: Your message of "Sat, 16 Nov 1996 16:04:37 PST."
             <E0vOuiz-00047c-00@uruk.org> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Sat, 16 Nov 1996 17:44:50 -0800
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>The situation is that FreeBSD does some weird stuff in
>"i386/i386/machdep.c" which interferes with correct autodetection of
>the amount of RAM installed.
>
>The existing bootloader checks the BIOS interfaces for lower and upper
>memory, and pass that to the kernel.
>
>The kernel checks the RTC values and used to always ignore the values
>passed by the bootloader.
>
>Currently, it does use the BIOS value passed by the bootloader for lower
>memory, because it was discovered that this was necessary to get APM and
>SMP code to work right.  It still ignores the BIOS values for upper memory,
>though.
>
>I would argue that the BIOS values should always be used, and the RTC
>values simply ignored unless something specific (like the SMP probe) needs
>them.

   I seem to recall that there was a problem with doing this on some systems,
but since my memory is so vague, I'm inclined to agree with you. :-) It's
probably that old FreeBSD bootblocks didn't pass in the BIOS information (via
the bootinfo struct)...but this was so long ago that I don't think it matters
anymore. Perhaps it should use the RTC numbers if the passed-in BIOS numbers
are zero?

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project