Mini-ITX, LinuxBios and DOC

Answering my own question for the group and google, I have been informed of the following sites:-

MiniITX Mainboard with DOC socket, available from

e.g. the BN860T, Approx 60 Euro without CPU. Very neat.

LinuxBios Experts and Linux Bios on VIA EPIA amongst others

- does not support initrd however.

Thanks to all who helped, Vincent

What about to use a DOM (Disk On Module) instead of DOC ?

Is this a problem? You know exactly what your hardware configuration is so I'd assume that you'll compile everything you need into your kernel.

Are there issues with, for example, having the root filesystem on a USB device? (IOW, the BIOS can handle loading the kernel from it, but the kernel can't handle running from it?)

--kyler

DOM has a IDE-like interface not only in SW but also in HW, so it's easier to use it instead of DOC.

B.Rgds,

Lawrence Lew

I was going to have a moduleless kernel and have my application and everything in the initrd.

The idea of linuxbios is that you replace the bios with a doc. YOu then program a bootloader which initialises the motherboards regsiters, loads the kernel and then can load an initrd from the doc. This allows quicker boot up time, custom display if you have one etc, along with the non-requirement for a root file system.

Both IDE ports are busy with CD rom drives. I dont want a compact flash to die converter which performs the same function either, nor do i want a usb boot device plugged into the internal usb ports.

The BN860T motherboard will fulfill my requirements.

Right, I think we all agree it's much easier to deal with DOM.

Why use it instead of an IDE-CF adapter and a CF card? Besides being amazingly cheap and readily available, the CF card can be easily reprogrammed by most any laptop. This makes development especially convenient in some situations. ("Oops! I just hosed the disk...")

--kyler

Besides the quicker boot, it doesn't buy much for your application, does it? Everything else you can do without touching the motherboard with much less expensive and more readily available hardware. (I've only read about the custom BIOS images but haven't implemented them. I'm confident it's fairly easy to do.)

Why the extra complexity? A compressed root file system is only an advantage if you're constrained by a tiny storage device. It's going to be hard to find a USB or CF memory device that small these days. It will be much easier to develop with a regular filesystem (which you can switch to writable when you need) and won't require so much system memory (not that it's a big expense).

It sounds like you have your heart set on making this difficult. If it results in more LinuxBIOS work, that great for me, but I'd still like to know if there's any real advantage to it (besides the value in tinkering).

--kyler

Not when the machine is booting. (I suppose that *is* a reason to use a RAM disk for the root filesystem.)

Any technical reason or is this just an emotional decision?

--kyler

The original post said that both IDE ports will be busy, with CD writers.

As you say, in the beginning, a flash disk could be used for boot. But I was hoping to produce a system with as few connectors and fiddly bits as possible, hence the DOC socket or LinuxBios DOC in a Bios socket. DOMs, CF and the like make this more fiddly.

Im looking to make the footprint as small as possible and as shallow as possible, which is further makes me fancy the DOC option.

Cheers, Vincent

----- Original Message ----- From: "Kyler Laird" Newsgroups: comp.os.linux.embedded Sent: Friday, September 19, 2003 4:10 PM Subject: Re: Mini-ITX, LinuxBios and DOC

usb

...and my post pointed out that they're *not* busy at all when booting. You realize you can have two devices on an IDE line, right?

Fiddly? O.k....

Hmmm...once you get so tight that you can't fit a tiny USB key in there, I suspect you're going to have trouble dissipating heat. Heck, just bending the power cable to keep it that low would scare me.

--kyler

Ah! I think a few of us have been talking past each other on this subject. I finally realized that you might be saying "ports" to mean "master and slave devices on a single IDE interface".

Is it the case that you only have one IDE interface on the boards that you've been checking? There are certainly Mini-ITX boards around with dual IDE adapters that would easily support two CD drives (independently even) along with a boot device. If you're having trouble finding some, let me know. I'm fairly sure that some of the ones I have are dual IDE.

--kyler

Firstly, Thanks to Kyler and Lewen and the others who have replied directly with this post.

The reason I wanted to have a CD writer on each of the IDE sockets was because I was wanting to write dual CDs simultaneously. I was under the impression I could not do this when connecting both devices, one as a master and one as a slave, to each IDE port or channel.

Since I have a CD writer connected to each IDE channel, I assumed I would not be able to use an IDE persistant storage device. This now looks like I was wrong since the IDE channel may be used for booting, decompressing to ram then running from ram, and can then be forgotton about.

The IDE CF converters I have toyed with are quite large and I was trying to go for the small sizes, hence I was attracted to the DOC option. I was already concerned with connectors for the slimline CD to conventional IDE cabling, and in my experience cables and connectors and adaptors can be a problem. The LinuxBios DOC option was doubly attractive since it allowed me to have a quicker boot time.

The Biscuit PCs I have seen tend not to have dual IDE ports but I would be happy to be proved wrong. I also need sound support, which is not always offered by biscuit PCs.

The Mini-ITX option just seemed to be a low cost route to developing a prototype to show off with, since the mothebroard is around the same size as the CD writer. I was looking at using one of the switchmode PSU plugged directly into the ATX power commector and use a wall cube PSU to provide a neat base unit.

Hope this clarifies my situation, Vincent

I think you're right to avoid that. Keep them on different interfaces.

Yes, that should work nicely for you. I don't know if there's any advantage to running the CD drives both as IDE "master" devices, but I think you should be able to do it and still boot from a "slave" device. (Strangely enough, I've had the need to do that on one of my machines.)

I have some large IDE-CF converters too (with RS-232 ports?!). More recently I've gotten much smaller ones from Mesa.

They're still a little larger than what I'd like.

Ug. Yes, I hate the CD connector thingies. The one I have falls out with the slightest nudge.

I would definitely try booting from USB. You should be able to get a nice compact easily-mounted system that will solidly connect to the USB header on the board. Because it won't tie up the IDE interface, you could even safely use it without expanding to a RAM disk. With a USB 2.0 device, the speed should be quite sufficient. And they're *cheap* and easy to find. Have a problem? Pull it out and stick another one in. Try that with DOC. It should make development much easier too since you can test one while you load another on your desktop machine.

I've only read about booting from USB memory but I haven't tried it yet. I'm thinking that I'll order some cheap tiny USB 1.1 devices

to get started.

I have several like that. They're great. Sometimes I even run them off of a 12V battery. So if you ever want to turn your CD duplicator into a "boom box"... (You could also add a small battery just to keep it alive if someone bumps the power cable.)

--kyler