4 Jun
2003
4 Jun
'03
9:55 a.m.
--- Tony Duell <ard(a)p850ug1.demon.co.uk> wrote:
I thought about suggesting that, but the hardware hacker in me wants to
keep it as simple as possible :-). I think I could make a Unibus master
and arbiter in a handful of TTL chips (look at the releveant bits of a
Unibus CPU printset -- it's not that complicated). Using a CPU sounds
like overkill..
There's also the issue that I wanted to keep stuff 'out of the way' I was
thinking it would be useful if the new host could do _anything_ to the
disk controller (that's one good reason to avoidthe BSD device drivers,
actually).
An alternative approach (and one that I'd
probably try) would be to use a
real RL11 (or similar), a Unibus (or as applicable) RAM card, and a
home-made bus master/arbiter that could tall the RL11 to read a sector
(using DMA into the RAM card) and could then read out the RAM to the host
computer. Doing something like that would let your PC (or whatever) talk
to just about any small DEC disk drive using the appropriate Unibus
controller.
If you are going to do that, why not use a DEC CPU? Why not just use a PDP-11/53 CPU board with local
serial and on-board
I don;t have one :-) Anyway, I'm more of a Unibus person...
If someone wants to design a microcontroller-based
Qbus/Unibus register
thumper from scratch, I'd consider building one. Best to define how
to talk to it from the outside before getting too far along on the design.
It's a pity that computers with lots of parallel I/O lines are so
uncommon, and the user ports are out of fashion now...
One thing I would _love_ to find is a portable-ish machine which can
write a disk that's readable on a PC, and which has at least 32 parallel
I/O lines, totally user controllable. At the moment I'm using an HP71, a
9114 disk drive, an 82165 GPIO interface and some homebrew hardware
(which is still undergoing hackery). Pity HP never made a real user port
for HPIL....
-tony