- Either check out svn.openmoko.org/developers/werner/ and go to
  developers/werner/smallsys/

- or

  Create a suitable build directory and cd to it, e.g.,

  mkdir -p $HOME/fun/developers/werner
  cd $HOME/fun/developers/werner

  Then exctract just the files you need for the task:

  svn co \
  http://svn.openmoko.org/developers/werner/{myroot,poke,pmu,wkalrm,smallsys}

  cd smallsys

- build the rootfs

  ../myroot/myroot small.myroot

  If myroot doesn't find the SVN directory, provide it in the environment
  variable SVN, e.g.,

  SVN=$HOME/fun ../myroot/myroot small.myroot

  There are complains about failure to download some files, lack of "rm",
  and busybox.postinst. They're harmless and can be ignored. The resulting
  rootfs should be about 4.5 MB (du -sh root).

- Copy kernel-config to your kernel's .config

- Edit CONFIG_INITRAMFS_SOURCE to point to the root directory of the small
  file system, e.g.,
  CONFIG_INITRAMFS_SOURCE="/home/whoever/fun/developers/werner/smallsys/root/"

- Build the kernel. It should be slightly smaller than 3MB.

- Install and boot the kernel. It will automatically mount the initramfs
  and enter a busybox shell.