My solution
was far more reasonable. Map it <VDM1> at 4000h and set a bit
to enable it (small hack). That way it used no TPA space and was still
faster than using a TTY. I later set up one of the NS* controllers that
way for a full 64k space. Of course I had to write my own drivers but it
was pretty trivial.
And hack the RAM board to be disabled when the VDM1 is enabled?
Ah, ever hear of phantom... part of the MDS-A and VDM IO hack was to set
them up to output Phantom, in both cases it was just a jumper required.
The disable was simpler, MDS-A has a rarely used sector interupt enable
latch and the VDM used a bunch of bits for windowshading, something I
considered useless and removed from the board (a few socket level jumpers)
and I had the bit I needed for enable. If they were enabled phantom was
generated, if they were not ram was there.
Allison