(last updated on Feb 2012)
I’ve been meaning to play with Plug Computers for some time now, as I need a low-power embedded system around the house. I recently bought a Soekris Net6501 (a pretty powerful Intel CPU, that even has VT support), but had annoying issues getting it working reliably. I ordered an ARM-based Dreamplug as an alternative (and as a bonus, the Dreamplug is 6x cheaper than the Soekris!). Here are my notes on getting it to work.
The Dreamplug arrived with a working installation, but running the absolutely ancient Debian Lenny. A dist-upgrade through to Wheezy led to bricking it almost immediately, and so I did a fresh installation from scratch.
For a fresh installation, place a USB stick of suitable size (greater than 2GB is best) into your functional Debian installation. Then:
fat16(I picked 150MB) and the remainder an
ext3partition for Linux itself. There are good instructions available on the Tor/Dreamplug wiki which show you how to do this.
$ sudo mount /dev/sdb1 /mnt $ sudo cp uImage /mnt $ sudo umount /mnt
You now need to use
debootstrap to install a fresh root image.
Because it is ARM and your main PC is probably an x86, you will need
to setup the QEMU CPU emulator. An extremely cool feature of QEMU is
that it can do transparent
emulation of foreign
binaries, so you can chroot directly into the ARM filesystem and run
commands as if they were x86. The
qemu-deboostrap command will
take care of this for you, if you perform the steps below (again,
assuming your USB stick is
$ sudo apt-get install qemu-user-static debootstrap $ sudo mount /dev/sdb2 /mnt $ sudo mkdir -p /mnt/usr/bin $ sudo cp /usr/bin/qemu-arm-static /mnt/usr/bin/ $ sudo qemu-debootstrap --arch=armel wheezy http://ftp.uk.debian.org/debian/
Now grab the kernel modules from the same place as your uImage (for 3.2.7, from here). Then, chroot into your fresh installation and untar them.
$ cd /mnt $ sudo tar -zxvf ~/sheeva-3.2.7-Modules.tar.gz $ sudo chroot /mnt $ depmod -a # edit /etc/network/interfaces # edit /etc/resolv.conf
The wireless setup involves some extremely crap firmware which
relentlessly kernel panicked for me, so I just disabled it by adding
the following to
/etc/modprobe.d/dpwifiap.conf, as I only want
blacklist libertas blacklist libertas_sdio
From there on, put the USB stick into the Dreamplug, and follow the rest of the boot instructions from the Tor wiki to interact with the Marvell BIOS and boot from the USB stick. I copied the contents of the USB stick onto the internal MicroSD, and it all boots standalone now.
One of the reasons I wanted an ARM-based setup is to experiment with the OCaml native code generation. Benedikt Meurer has been doing some excellent work on improving code generation for embedded systems, including support for 16-bit Thumb code, exception backtraces, and dynamic linking and profiling.
Once Linux was up and running, compiling up the latest ocaml-trunk was straightforward.
$ sudo apt-get install build-essential git $ git clone http://github.com/OCamlPro/ocp-ocaml svn-trunk $ cd ocp-ocaml $ ./configure && make world opt opt.opt install
This compiles the bytecode and native code compilers, and then compiles
them again using the native code generator. This takes a while to do on
the poor little ARM CPU. Once that finished, I compiled up a few simple
modules and they worked great! Since the trunk of OCaml is a development
branch, you may run into a few packaging issues (use the very latest
OASIS to regenerate any
setup.ml, and you will need a small patch
until PR 5503 is