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<title>M-Systems Disk-On-Chip 2000 and Linux</title>
<meta name="keywords" content="Disk-On-Chip, CompactFlash, Compact Flash, Disk On Chip, M-Systems, Linux, MTD, Flash, Memory Technology Device">
</head>
<body bgcolor="white">
<h1 align="center">M-Systems Disk-On-Chip 2000 and Linux</h1>
<HR>
<P><B>Please reload this page often, or join the <A
HREF="./">Linux-MTD</A> mailing list to keep updated of
further developments. <A HREF="#latest">Latest news</A> is at the
bottom of this page.</B><BR>
<A HREF="mailto:Dave@infradead.org">DW</A>.
</P>
<P>M-Systems' Disk-On-Chip 2000 is now supported by the
<A HREF="./">Linux Memory Technology Device subsystem</A>.
M-Systems have provided me with complete specifications and sample
hardware, and are also being very helpful when I ask them stupid
questions.</P>
<P>We have recently received a large amount of new code for the NFTL
driver from Fabrice Bellard. The code now handles bad blocks and
properly implements ECC, along with a number of other bug fixes.</P>
<P>Also, the DiskOnChip Millennium hardware is now supported, and the
<A HREF="http://www.acl.lanl.gov/linuxbios/index.html">LinuxBIOS</A>
project are using the DiskOnChip Millennium to hold their system
image and also in many cases the root filesystem.</P>
<P>I haven't tested it myself recently, but I believe it should be
considered to be in late beta test. The only remaining issue that
I'm aware of, other than the need to clean up the code a little and
provide some better documentation, is that it does all flash
accesses with interrupts disabled, which is a little suboptimal. That
ought to be simple to fix.</P>
<HR>
<P>There is also a binary-only Linux driver for i386 systems available
from M-Systems themselves, but this suffers the from well-known
problems of binary drivers, in addition to which, if it is to be used
as a root filesystem, it must be statically linked into your kernel,
which places <B><I>you</I></B> in blatant violation of the GPL if you
distribute a solution using it.</P>
<P>If you aren't already aware of the nature of the the problems with
binary-only drivers, then you can find more information in the ALSA
Project's <A HREF="http://www.alsa-project.org/call.html">Call to
Hardware Vendors</A>. There is also <A
HREF="http://lwn.net/1999/0211/kernel.phtml">a piece in the Linux
Weekly News</A> about Linus Torvalds' attitude to binary-only drivers
- why he insists that they will be broken, and often. In Linus' mails,
which are available <A
HREF="http://lwn.net/1999/0211/a/lt-afs.html">here</A>, <A
HREF="http://lwn.net/1999/0211/a/lt-idc.html">here</A> and <A
HREF="http://lwn.net/1999/0211/a/lt-binary.html">here</A>, he says:
<BLOCKQUOTE><I>
Basically, I want people to know that when they use binary-only
modules, it's THEIR problem. I want people to know that in their
bones, and I want it shouted out from the rooftops. I want people to
wake up in a cold sweat every once in a while if they use binary-only
modules.
</I></BLOCKQUOTE>
<HR>
<H2 ALIGN="center">Current Status</H2>
<P>
I haven't made a snapshot recently, but the latest CVS tree contains
all the above-mentioned code, and should be stable. Please test it
in either a 2.2 or 2.4 kernel and let me know how you get on.
<BR>
DW. 28/11/0
</P>
<hr>
<H2 ALIGN=CENTER>Updates</H2>
<P><B>Update 6/7/99 9pm (BST): </B> I have now heard again from the
President of M-Systems. He has not yet managed to arrange a meeting
to discuss the issue internally, but he promised that he will get
back to me by the end of the week with a proposal for a solution.
He concludes with the following sentence:
<I>"We are looking forward to the success of Linux and we want to be part
of it."</I></P>
<P><B>Update 8/7/99: </B> I have received a message from the Vice President
of Research and Development at M-Systems, Amir Ban. He responds to some
of the technical issues to which I refer above. I have included his
comments after each of my points, with a response from myself if
appropriate. However, this was limited to technical concerns - the
legal problems and other difficulties arising from the binary-only nature
of the drivers were not addressed. We are still discussing possible
options with regard to those.</P>
<P><B>Update 9/7/99: </B> I have heard again from Amir Ban, explaining
their reasoning and their concerns. His mail can be found <A
HREF="msys-response.html">here</A>, along with my response to it,
and my interpretation of the patent issues.</P>
<P><B>Update 19/7/99: </B> The latest word from M-Systems seems to be that
they are willing to give me enough details to write a driver capable of
reading, writing and erasing the Disk-On-Chip 2000 hardware. The
programming spec currently exists <I>"only as an internal paper
and is being worked on to be suitable for distribution."</I>
They haven't yet given an expected timescale for this.<BR>
They're extremely reluctant to release details of the NFTL filesystem,
so we may have to come up with an alternative before the Disk-On-Chip
is actually usable under Linux.</P>
<P><B>Update 25/7/99: </B> The <A
HREF="http://www.linuxjournal.com/issue64/">August issue of Linux
Journal</A> has just arrived, and incorrectly states that the driver
developed by IGEL for the DiskOnChip 2000 is available under GPL from
M-Systems' web site. I have responded to the Editor, Marjorie Richardson,
about this, and I hope that a correction will be published in the
next issue.</P>
<P><B>Update 1/8/99: </B> Despite sending another reminder, I still have
not heard from Linux Journal regarding their article on IGEL which
mentions the Disk-On-Chip. This is surprising, considering the
seriousness of their mistake. I hope that they contact me soon.</P>
<P><B>Update 2/8/99: </B>I have heard again from M-Systems. They have
provided me with the NFTL specification, and also the data sheet and
programming specification for the Disk-On-Chip Millennium. I expect to
be able to produce a GPL'd Linux driver for them very shortly. With
this, every objection I have to using the Disk-On-Chip under Linux has
gone. M-Systems have responded genuinely to our concerns, and have
provided us with documentation which contains their hard-earned
intellectual property. I can now wholeheartedly recommend their products
for use under Linux. Now, I must get my head down and produce some code.
</P>
<P><B>Update 10/8/99: </B>A preliminary read-only driver for the
DiskOnChip 2000 and NFTL has been incorporated into the latest release
of the MTD code. In addition to complete documentation and a contact
point for further questions, M-Systems have provided me with sample
hardware for the DiskOnChip 2000 and DiskOnChip Millennium. These
devices will soon be completely supported by Linux.
</P>
<P><B>Update 17/8/99: </B>I now have the ECC error
detection working. It's taken longer than I expected, because there are
subtle differences between the DiskOnChip 2000 (with which I'm testing)
and the DiskOnChip Millennium (for which I have the specs). M-Systems
are being extremely helpful and pointing out the places where I've gone
wrong, however. Now this is working, I can get on with implementing the
write support, first in the DiskOnChip hardware itself, and then in the
NFTL layer.
</P>
<P><B>Update 20/8/99: </B>At last I have some form
of write support for NFTL. It seems to work OK on the NFTL filesystems
that I've formatted myself, but it gets confused on the NFTL filesystems
which are produced by M-Systems' drivers. I need to correctly handle
the cases where there are multiple Chains for the same Virtual Unit;
which isn't covered in the spec, but it's not possible to replace a Chain
without having the device in this state for a short period of time.
</P>
<P><B>Update 1/11/99: </B>I can now write to the NFTL
repeatedly without confusing the M-Systems driver - I can bash on it
for a long time, and it doesn't seem to leave it in a state where their
driver no longer understands it. I'm not sure whether this is a good
thing or not - I'm not aware that I did anything to fix it, and I don't
like bugs that just mysteriously disappear. <B>More testing and feedback
is required - please.</B>
</P>
<P><B>Update 31/1/00: </B>We can now boot Grub from
a DiskOnChip - we can replace the DiskOnChip firmware with a version
of Grub, which will be automatically started from the flash.<BR>
That's the good news. The not-so-good news is that we haven't yet
got Grub itself to support the DiskOnChip, so it's fairly pointless
for now - but it's a good start. Necessary, but not sufficient.</B>
</P>
<P><B><A NAME="latest">Update 28/11/0: </A></B>People seem to be linking
to this page so I suppose I'd best update it. I think the NFTL and
DiskOnChip driver code is basically almost complete now. All that remains
is some final cleanups and a large amount of testing. I'll see if I
can get it into the 2.4 release.<BR>
In related news - Grub is also reported to be working completely
with the DiskOnChip 2000, and someone's working on getting it to
work with the Millennium.
</P>
<HR>
<address><a href="mailto:dwmw2@infradead.org">David Woodhouse</a></address>
$Id: doc2000.html,v 1.2 2000/11/28 10:25:30 dwmw2 Exp $
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