Re: how to tell linux (on x86) to ignore 1M or memory

From: Bodo Eggert <7eggert@gmx.de>
To: Rene Herman <rene.herman@gmail.com>,
	Dave Jones <davej@redhat.com>, Neil Brown <neilb@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kyle McMartin <kyle@canonical.com>,
	linux-kernel@vger.kernel.org, alan@redhat.com,
	bcollins@ubuntu.com, pjones@redhat.com
Subject: Re: how to tell linux (on x86) to ignore 1M or memory
Date: Fri, 20 Apr 2007 23:39:54 +0200	[thread overview]
Message-ID: <E1Hf0pe-0001Ne-J8@be1.lrz> (raw)
In-Reply-To: 8c6EE-4Jj-5@gated-at.bofh.it

Rene Herman <rene.herman@gmail.com> wrote:
> On 04/19/2007 04:18 PM, Bart Trojanowski wrote:

>> I need to preserve some state from the bios before entering protected
>> mode.  For now I want to copy it into some ram accessible by real-mode,
>> say the last megabyte visible in real-mode.
>> 
>> What's the easiest way to have linux ignore the megabyte starting at 15M?
> 
> Note that real-mode can only access the first megabyte (*) and not the first
> 16. 16MB is the 16-bit protected mode (286) limit.
> 
> (*) well, the first 1M + 64K - 16 bytes using segment FFFF assuming A20 is
> enabled and x > 1 in x86...

Interrupt 15h, function 87h allows copying from/to extended memory.
You might like to look into Ralph Brown's interrupt list for more details.

You could also cpio-gzip the data and append it to the initramfs.
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