>Does anyone have pointers for 3maxplus hardware documentation?  

There is no publically-available documentation.  The source is all we
have.  (The only models for which DEC released the documentation was
the 3100 and the 5000/200).

The mouse works on my 5000/150 running -current, so it should work on
a 5000/240.

The other caveat is that the mouse is initialized into positional
mode, if and only if the kernel detects RCONS as the console.

Using a serial console (via the PROM "setenv console s") and still
running X doesn't work (since the mouse-init code hangs if theres no
mouse present).  Is that what you're trying to do?
The simpe fix is to switch back to rcons.

On -current, the only other likley candidate is whether EGCS's better
codegen has broken the timing-loop code in DELAY().  If you ratchet up
the
       DELAY(150);

in sys/arch/pmax/dev/lk201.c, to say, DELAY(300), does that help?

>Alternately, if 1.3.3 fixes the r4k gdb problems, I could just switch to
>1.3.3... all I want is an OS where both the mouse and gdb work.  ;-) 

No, I dont think michaels' GDB changes made it into 1.3.3.  (we never
got to a consensus on what to call the necessary callbacks, or putting
no-op versions of them into all other ports.)

Michael -- maybe we should release a version of the patch for 1.3.3,
so pmax users with r4000s or r4400s can at least apply it via source?