Supercomputing adventures with a MegaST/4

[rubber_jonnie]

So is it possible to stack the boards one on top of the other to improve density?
If not then why have the sockets at all?

As far as I know, the cannot stack TRAMS. I *think* the sockets are so you can probe signals easily.

I kind of thought that would be the case, especially since the components are too tall to allow stacking, but wouldn't it be cool if you could

[dml]

I did see a post somewhere on an old Transputer discussion forum where they were actively talking about 'stacking Trams'. I don't know if I bookmarked it... will look later.

Anyway it seems unlikely because the serial links are just an RX/TX pair and if you stack them together the Transputers won't know which message is intended for which unit. Even if you had the software sort that out with a complicated multicast protocol, the link controller would lose packets on colliding signals.

But maybe someone thought of all that


I'll follow up soon with more progress on this thing...

[dml]

Great find. Several employees here are former inmos engineers who say they have old boards in their attics and I've been begging them to bring them in / loan or sell them to me. So far just a few pictures no hands on

So cruel of them I hope they change their ways and drop you some boards.

[dml]

The next incremental step towards desk-flames was to plug the thing into a VME backplane - one that is not designed for it at all - and see if I could find any compatibility problems with pinouts/conflicts. Especially the power hookups.

I beeped out various points and confirmed 5V/GND where it should be expected and nowhere it wasn't expected. I wasn't really exhaustive with that but it was 'good enough' for the next step.

I obviously removed all the TRAMs before taking things further in case of accidents. They were bolted down with extremely annoying nylon bolts with some 1980s version of nail-varnish-threadlock stuff. I got most of them off by applying IPA and cracking the varnish with pliers before attempting to remove them. A few 'died' in the process when I ran out of patience.

backplane.jpg (718.5 KiB) Viewed 51 times

I powered the backplane from a 5V bench supply. The backplane has nice chunky power terminals with big bolts. That might come in handy later.

backplane-power.jpg (652.43 KiB) Viewed 51 times

...especially since the backplane alone sucks more than an Amp just for termination.

vme-amps.jpg (342.62 KiB) Viewed 51 times

Anyway nothing blew up yet and I could see power at the correct points on the ICs etc. Good for the next step....

[dml]

The next small step in the adventure - confirm the local 5MHz oscillator is appearing on the clock pin of all 8 TRAM slots.

test-clock.jpg (852.93 KiB) Viewed 26 times

...which it is!

tram-clock.jpg (330.91 KiB) Viewed 26 times

Everything gets more difficult from this point onwards

[rubber_jonnie]

Good work so far, looking like a real interesting project so far.

[dml]

Good work so far, looking like a real interesting project so far.

Thanks!

I have a bit more detail to follow sometime today or tomorrow - after which we'll be fully caught up with my progress trying to reverse it.

[stephen_usher]

You do realise that the "narrow" VME bus in the TT is compatible with the "wide" one on that backplane don't you?

"Wide" cards can usually run in "narrow" mode.

Of course, the TT doesn't support VME bus mastering, which may be an issue if trying to interface with that card.

[dml]

You do realise that the "narrow" VME bus in the TT is compatible with the "wide" one on that backplane don't you?
"Wide" cards can usually run in "narrow" mode.
Of course, the TT doesn't support VME bus mastering, which may be an issue if trying to interface with that card.

I suspected as much but wasn't sure if it fully compatible. I will post a bit more on the connector soon.

However given the nature of Transputers and the limited signals required - and some other details I haven't revealed yet - it seemed like this would be a less fiddly approach to waking it up, at least for now...