From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <8fb16d83a62dd47d262ae5f8020045db@gmx.de>
To: lucio@proxima.alt.za, 9fans@9fans.net
Date: Mon,  7 Mar 2011 12:50:29 +0100
From: cinap_lenrek@gmx.de
In-Reply-To: <20110307110755.GA1893@fangle.proxima.alt.za>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Subject: Re: [9fans] realemu update
Topicbox-Message-UUID: b7f850fc-ead6-11e9-9d60-3106f5b1d025

> On Mon, Mar 07, 2011 at 11:39:10AM +0100, cinap_lenrek@gmx.de wrote:
> > /dev/realmodemem is just an image of the first megabyte of
> > physical memory that is addressable from 16 bit realmode.
> >
> That being where the machine's BIOS resides, if memory serves.
> Plus whatever can fit in there if one chooses to use the space.
> I'll understand things better with the fesh background, thank you.

yes, exactly. it also contains the data setup by the bios.

this is the memory map from realemu main.c, one entry for each
64k block:

static Bus memio[] = {
	/* 0 */ memory, rmem, wmem,	/* RAM: IVT, BIOS data area */
	/* 1 */ memory,	rmem, wmem,	/* custom */
	/* 2 */ nil,	rbad, wbad,
	/* 3 */ nil,	rbad, wbad,
	/* 4 */ nil,	rbad, wbad,
	/* 5 */ nil,	rbad, wbad,
	/* 6 */ nil,	rbad, wbad,
	/* 7 */ nil,	rbad, wbad,
	/* 8 */ nil,	rbad, wbad,
	/* 9 */ memory,	rmem, wmem,	/* RAM: extended BIOS data area */
	/* A */ memory,	rmem, wrealmem,	/* RAM: VGA framebuffer */
	/* B */ memory,	rmem, wrealmem,	/* RAM: VGA framebuffer */
	/* C */ memory,	rmem, wbad,	/* ROM: VGA BIOS */
	/* D */ nil,	rbad, wbad,
	/* E */ memory,	rmem, wbad,	/* ROM: BIOS */
	/* F */ memory,	rmem, wbad,	/* ROM: BIOS */
};

on startup, we read in all the readable memory from the host machine.
this means, that if the host machine is not a x86 with a bios that
mapped the roms for us it will not work.  to make this work have to do
the same thing the bios on a pc makes like setting up a realmode
interrupt table and discover and map in the vga roms.

> > the write returns when the BIOS call returns and the machine
> > state can be read back from /dev/realmode.
> >
> That is a neat idea.

yeah, its the power of filesystem abstraction all over again :)

also, with realemu, you can interrupt the write to /dev/realmode in
case the code hangs in a endless loop.  otherwise it will return if
the code comes back from the interrupt call to the bios or when the
code produces some kind of exception.  errstr will be set to a string
describing the exception and the exception number will be in u->trap
when reading /dev/realmode back.

--
cinap