Probs w. M3119 CXY08 MUX on VAX VMS 7.3

Johnny Billquist bqt at
Tue Aug 18 14:48:51 CDT 2015

On 2015-08-18 21:29, Paul Koning wrote:
>> On Aug 18, 2015, at 2:00 PM, Johnny Billquist <bqt at Update.UU.SE> wrote:
>> On 2015-08-18 19:05, Jon Elson wrote:
>> ...
>>> Most likely, some board was added or removed from the system before you
>>> got it, and it caused the vector to now be wrong.
>> The vector is usually not the first victim. The CSR address is, which cause all access to the controller to fail. But the vector often also move, causing the more obscure errors. However, most DEC OSes actually autodetected the vetor, and did not care about the actual floating assignment rules for the vectors.
>> The thing is, all you need is to trigger an interrupt on the device, and then notice at what vector it came in, and then you go with that. This only fails when several devices happen to use the same vector.
> Typically that would be detected as a configuration error — two devices whose autodetected vector matches.  One of the offending devices (the one seen later, presumably) would end up disabled.

Ideally yes. However, at least RSX I think fails on that. As device 
vectors are detected. they are installed. So the vector detection code 
does not get called for the second device using the same vector, but 
instead you get a spurious interrupt in the autoconfiguration.

But that is just some vague recollection, and I could be wrong. In 
normal operations, RSX does not probe, but relies on what was discovered 
during sysgen.

>>> In some cases, you had to force a device to be at a non-standard
>>> address, possibly because a 3rd party device could not be configured at
>>> the address the DEC enumeration scheme wanted to put it at.  This was
>>> pretty easy to do in later VMS systems.
>> Very easy to do in RSX-11M-PLUS as well. A simple one line command, which can be done on the running system.
> And RSTS, starting with V5B.

Cool. I had no idea. Plain RSX-11M cannot. The CSR and vector is set at 
sysgen, and you can (of course) patch the memory, but there is no 
command to reconfigure the running system.

-11M-PLUS got all that as a part of the support for the 11/74, where you 
were expected to be able to move devices around in the running system. 
Hot-pluggable, in a way. And it also applies to CPUs, memory and 
buses... It's a rather complex subsystem, but extremely nice.


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