There's a Users' Guide at

      http://www.necel.com/home.nsf/Main?ReadForm&Microprocessors

which seems to have info on touch-screen, audio, etc
(I say "seems" as acroread4 crashes on my laptop display)
The info may help resolve startup issues with netbsd/hpcmips
on e.g.,  Cassiopeias with this CPU.

The user's guide also documents the vr4121 "macc" instructions.
Anyone know of patches to binutils to use these insns?
All I can find is the older vr4111 "macc16".