Unibus card interference and RK11 placement (was RE: TSX-Plus Password Hacking & Other PDP-11 Issues)

From: Rick Bensene <rickb_at_bensene.com>
Date: Thu May 8 17:50:01 2003

I wrote:
> > Here's another question for you DEC folks:
> >
> > The system has the main backplane... then there's the RK11
> > backplane...
> > (then) a 9-slot expansion backplane.
> >
> > Question is: Is this correct? Should the RK11 backplane... be
> > situated BETWEEN the main bus and the expansion bus, or
> should it be
> > located at the end?
>
To which Ethan D. replied:
 
> It kinda depends on what else is in there. There are some
> peripherals that want to be very close to the CPU because
> they can't buffer
> operations and would starve if some other device were in
> front of them. The RL11 should have a "silo" (the RL8A does,
> I'm pretty sure) that allows it to be somewhat patient about
> initiating transfers. I would expect the RK11 to be less
> sophisticated, and more sensitive to timing issues. Ethernet
> cards and streaming tape controllers are other classes of
> devices that tend to want to be near the front. Terminal
> cards and line printer controllers tend to be more tolerant,
> owing to the relative slowness of the I/O (compared to disk
> and network).
>
> So... if it's there right now, I'd probably leave it, unless you run
> across a comment in a DEC handbook that suggests that it
> needs to be somewhere else. Unless you are getting data
> errors with peripherals behind it, it's probably not hurting anything.
>

Well, I went ahead and populated the RK11 slots with the RK11 backplane
in the 'middle' position between the main bus and the DD11-DK expansion
backplane.
I put M9202 Unibus jumpers connecting the main backplane to the
RK11 backplane, and another connecting the RK11 backplane to the DD11-DK
expansion backplane.

I carefully checked to make sure NPG & the four BG signals were getting
across the whole
bus. I wire-wrapped jumpers on the DD11-DK expansion backplane to
provide continuity for the
four BG signals across the empty slots in the DD11-DK, and dougble
checked everything.
I powered up, no smoke or anything, but the machine wouldn't boot off of
the RL01. It
would halt at 000002, with no sign of activity on the RL01. So, I
figured that I'd
done something wrong. I swapped the position of the RK11 backplane to
the end of
the bus, and put the DD11-DK in the middle. I again double-checked my
NPG and BG wiring,
and all seemed OK. I moved the RL11 to the first slot of the DD11-DK
backplane, and
put a grant continuity card in the D section of the slot in the main bus
that was
vacated by the RL11 (and while I was working on the bus, put the NPG
jumper on that slot).
This time when I powered up, everything worked. I can now talk to the
RL01, an RK05,
and the RX02 drives. The mystery is why it didn't work before and did
with things
swapped around? Oh well, sometimes mysteries are better left unsolved.
I'm just happy
that things are working...and I've got lots of slots free to populate
with other things
that I may scare up over time.

Thanks to Ethan for his great advice. I could probably put the RK11
backplane back in the
'middle', but things are working as they are, and I've done a lot of
copying back and
forth between the RL01 and the RK05, and there doesn't seem to be any
kind of problems with
them getting in the way of each other in terms of bus timing.

Now to try to get the DZ11 in there and working.

Rick Bensene
Received on Thu May 08 2003 - 17:50:01 BST