Hmm. There *are* rom routines to talk to the console; while working
for MIT Project Athena (around 1987), I did get a bootable "Hello
World" working for both the VSII and the VS2000, though it ended up
needing to make slightly different ROM calls for each. Most of the
information was obtained from disassembly; if that's considered
acceptable, I'll try to dig it up...

The 4.3 port that MIT LCS used did have working console drivers for
both (or rather, for the qvss, qdss, and sm devices) but as far as I
can remember it was derived from DEC code.