Re: [linuxdc-dev] VMS flash handling

[Paul M. <pm...@mv...>]

On Wed, Jul 04, 2001 at 05:49:44PM +0200, Frederic SOULIER wrote:
>   In France, this costs about $30. So 1MB is enough for a full linux
> kernel (compressed or not), I wondered if booting my dreamcast from
> MAPLE bus was possible ? It would be very fine for me, since these kinds
> of "Visual Memory" are usually shipped with serial / parallel port or
> USB cable + interface for PC.
>=20
This all depends on how you intend to access the thing and how exactly you
want to boot. I've seen a number of these VMU's that have interface cables,
and the only software I've seen for them interact with the device while
keeping the vmufs intact so you can hex edit a rom dump and sync it back up.

The only problem with this is that you need a firmware that is intelligent
enough to communicate with maple, and you need to be able to pull down the
kernel image into memory in blocks, as you don't have any direct access to =
the
device itself. All you can do is read/write blocks from the VMU over maple,
where you're required to know the port and unit id.

So, in theory, you could hack something like RedBoot to be able to handle
maple, and simply read in the kernel image one block at a time.. then map
it into memory, and set the start address to the beginning of the mapped
region, and boot from there.

You wouldn't really get much benefit from this in my opinion, but oh well.

>   So after cross-compiling, you should have only to upload the code to
> the flash and then boot your DC from your joypad ! :)  (kidding, but
> this could be more flexible than a home made serial cable).
>=20
>   Well, does anyone know if all this is possible ?
>=20
Writing is still a touchy subject. I've been working on an MTD driver for
the VMU, though it interacts with the device over maple directly, and
the block reads/writes are handled by an underlying flash mapping driver.

The upside to this is that you can fully use it like any other embedded
storage device, but you have to do it over maple.. which requires having
the DC already booted and writing it from there.

I suppose you could extend my flash mapping driver to communicate over
serial in addition to maple.. but that'd be pretty useless.

The only other option you have, is to try and dump to flash raw data that
doesn't comply with the vmufs or any other filesystem, and then try and
map that into memory.. that'd be the simplest way to go about it, but it
renders the VMU pretty much useless for anything else until you can restore
the vmufs.

Regards,

--=20
Paul Mundt <pm...@mv...>
MontaVista Software, Inc.