M7264 Troubleshooting

Noel Chiappa jnc at mercury.lcs.mit.edu
Wed May 29 06:17:03 CDT 2019

    > From: Josh Dersch

    > how is the backplane in the H11 currently configured? (i.e. what boards
    > are in what slots?)  Could the issue here be something as simple as a
    > break in the qbus due to a misplaced board?

He did mention that he had the console card in the slot next to the CPU, which
I think is what you're referring to - but it shouldn't matter for ODT, which
doesn't use interrupts, only programmed I/O.

A QBUS system will work fine without continuity of grant (interrupt, DMA)
lines to boards which only respond to DATI/DATO (memory, non-interrupt I/O,
etc). Just for grins, I took my -11/03, and plugged the console card in a
bunch of slots down, leaving several empty slots between it and the CPU, and
it worked 'fine': ODT was fine, and it would run "BR ." programs fine, too.

So unless there's actually a break in one of the 'broadcast' bus lines (e.g.
BDALxx, etc) on that backplane, between the CPU slot, and the slot the console
card is in, or something like that...

I suppose it would be worth while checking BDALn, BSYNC and BDIN _on the
console card_ (I'm not sure where he was looking at them, before) just to
rule out the broken bus line possibility.

One thing that's bugging me, though; he said "BDAL3-13 .. are all active and
jump around in some manner". But for the ODT microcode loop trying to read the
console CSR, i.e. 0177560, BDAL7 (0200) and BDAL3 (010) should be 0, i.e.

So why are they jumping around too? Is this somehow related to the odd behaviour
I was seeing on my machine with no console card, where the BDAL line was behaving
in a way I couldn't understand?

I'm going to look into that more, to try and understand what I'm seeing there,
but it won't be today, which is 'crane day'!


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