Supercomputing adventures with a MegaST/4

[dml]

This afternoon I decided to see if I can get light out of the thing - get the Atari to see it. So far it has just been a lot of DMM checks, making notes and diagrams and stuff but I'm a bit more confident now that I can wire it up. I also wanted to get a bit more done today instead of waiting for more parts to show up.

I installed a header on the Transputer link connector on the ATW800/2 and started looking for an IDC plug/ribbon to carry the signals to the carrier board. As usual, could not find what I was looking for - and to avoid spending the rest of the weekend digging in boxes I fell back to some of those sketchy dupont connectors.

Unfortunately the dupont jumpers are far too short and this makes wiring it up really annoying. That's what happens when you can't wait a few extra days :p

To work around this I tried feeding the signals into the 2nd slot on the row, relying on the internal connections carrying that to the 1st slot in that row, where the Transputer/TRAM is actually installed. I used link 2 since its on the same row as the control signals and helps with the short wires.

I then started MUPFEL and ran rspy. I did not have success with this - it only detected the 3 Transputers usually present. However I noticed that power cycling the carrier caused the green LED on the ATW TRAM (the one it is linked through) to flicker for a few seconds.

I switched things around and moved the Transputer to the slot on the side near the ATW, fed the signals directly into the TRAM pins (these ones have small sockets on top) and tried again.

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Powering the carrier again caused flickering on the ATW TRAM LED.

This time running rspy though...

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So it has been seen by the Atari, across the external link.


It is not working reliably though in this config - rspy only detects it once. A second try shows it missing. Power cycling the carrier brings it back. I'm pretty sure the RESET net is floating on the board since my previous RE work showed it sitting at 1.6v and I kept that in mind while trying this so it's not completely unexpected that the unit would not be detected or would be flaky.

The fact it showed up at all in rspy though is a big step forward.

[dml]

Have been a bit unwell and things are moving slower... but I did make a bit of progress since the last post.

While I did get the TRAM to show up in the rspy query last time, I was cheating a bit by tying it directly on its pins. It works as a hack but I wanted to know if a Transputer can be addressed from the bus - and so, could potentially pass messages across slots. This is a bit more complicated and relies on information I had figured out about the board being accurate...

I moved the TRAM to slot 4, which is where the preferred entrypoint (slot 4, link 0) should be for an inter-board connection.

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I then started putting together a small buffer interface board which should allow the ATW800/2 to work with signals exposed on the backplane. This should make the ATW800/2 host appear as just another VME card.

bufferboard.jpg (468.3 KiB) Not viewed yet

As described in an earlier post, those TRAM signals are not exposed directly but are translated for compatibility with the other cards sitting on the same bus, including the original host which would have been in VME slot 1.

It seems the device (when complete with all cards) was something intended for video processing - the host card had analog video in+out - but it's actual purpose I don't know.