K, all relevant commands are in fact symlinks to busybox.
The manual for it is pretty informative:
http://www.busybox.net/downloads/BusyBox.html
Links to sleep and halt might be something different and
called those names just for developing purpose. I assume
that /bin/poff is the binary to make power off. There is also
interesting "check" binary, which resembles nothing to give
a clue. My best bet is that binaries are compiled with hard
coded periods for sleep and power off. Only "show_pic"
makes me think it might show the book cover, but I'm not
sure. If something has to be added, there is no place to be
picky, since this is embedded system. Maybe /etc/init.d/rcS?
At first glance, seems that it has to be recompiled to get
some tweaks.