Re: Install problem, BIOS/Probed memory mismatch (fwd)

["Geoff O'Callaghan" <hackcat@banzai.apana.org.au>]

Greetings,  I thought that i'd move this thread out of misc into 'tech' as
it's a little beyond 'users questions and answers'.  There may well be the
same people listening but i'll give a quick summary of the problem.

* 486DX2/66 16Mb memory - OpenBSD using probing determines incorrectly
that I have 56Mb memory and the boot fails.  There are no bios
setup options relating to installed memory.  
* I should really use sendbug to report the problem, but as I can't
install OpenBSD that's a little hard to do!

Could someone build me a floppy22.fs with EXTMEM_SIZE set to 8M (should be
enough?) in /src/sys/arch/i386/i386/machdep.c  (thats the filename
according to cvsweb) or at least tell me who builds the install disks and
i'll intimidate them into doing it by towering over them and talking in an
Australian Accent ;-)

Once i've actually got OpenBSD installed I can research the problem
further.

Many Thanks

Geoff

---------- Forwarded message ----------
Date: Sat, 27 Dec 1997 05:19:26 -0700
From: Theo de Raadt <deraadt@cvs.openbsd.org>
To: Geoff O'Callaghan <hackcat@banzai.apana.org.au>
Cc: Michael Shalayeff <mickey@lucifier.dial-up.user.akula.net>,
    misc@openbsd.org
Subject: Re: Install problem, BIOS/Probed memory mismatch 

> Further to my last posting, i've discovered that OpenBSD does not trust
> the bios when it comes to determining the amount of extended memory.  It
> appears that it detects Extended memory by probing page-by-page through
> the address space, rather than asking the BIOS.

It does trust the BIOS if the 'new style' BIOS call exists which
explains the memory in the system more thoroughly.

If that new style BIOS call does not exist, it uses probing.

> How do I override this action?  Linux uses a different approach to this
> 'bios problem' by allowing a 'mem' boot option to specify memory sizes
> larger than that reported by the bios.  Wouldn't it be better to include
> this as a boot option and allow it to be specified in /etc/boot.conf

I don't think you can yet.

> I don't know (yet) why my system fails on the memory probe test -
> basically telling me that I have memory which I don't have!!! Can anyone
> tell me the location of the source code which does the probe?

I bet it tells you that because your system does memory aliasing,
basically meaning that it re-maps the same memory higher up.

> It also appears that in /src/sys/arch/i386/i386/machdep.c I can specify
> EXTMEM_SIZE and basically just set the size of extended memory - the real
> question is.....how do I get a floppy22.fs disk with any of the above
> capabilities.

You'd have to build one yourself.  That's a real pain in the ass.

The right solution is to have the bootblock memory probing code be
more careful, such that it detects such aliasing problems.

> All the above is stuff that I have gleaned from a brief (internet link
> just too damn slow) look at the source via cvsweb and could be completely
> wrong :-)  

Good research.