> On Jul 31, 2019, at 1:34 PM, Geoff Conway <gcon...@bigpond.net.au> wrote:
>
>> ...
>
> There is a reason for mentioning the OS side of things and while in the real
> world the majority of PDP11 peripherals are set by switchpacks on the cards
> (been there done that) - the device code for that peripheral (if it's
> intelligent?) would (presumably) read those register values and load them
> into itself so it knows what addresses to respond to. In sysgen/netgen
> (whichever being relevant) the CSR/vector values for every peripheral are
> then manually entered by a human and the system/DECNet built.
That depends on the OS.
I think most OS know the floating CSR rules and use that to identify the
devices; you specify CSRs manually only if your address settings don't conform.
Similarly with vectors: the OS may implement the float vector rules to compute
the vector addresses for the devices. Or it may do what RSTS does, which is to
"poke" each device at boot time to make it interrupt, then remember what the
vector address was. So RSTS requires float CSRs in order to autoconfigure
devices but doesn't mind what the vectors are so long as they are all unique.
> ...
> The 3 exceptions are all the 3 devices I included in my simh qbus
> configuration and when I entered the "show dev" command prior to booting the
> OS disk all of those simh devices had CSR values but no vectors - devices
> DEQNA=XQ/XQB; KDA50=RQ/RQB and finally TK50=TQ.
> Prior to entering the OS they had <no vector> against them and after the OS
> was booted into a fully configured system and then finally shutdown those
> same 5 simh device then had their vectors assigned.
>
> Why ?
After reset, the vector address is not set. Once the OS programs the vector
address by appropriate commands to the device, it remains in effect until
cleared. Shutdown (on the OS you are using) apparently doesn't do a reset so
the vector remains set to what the OS assigned.
> ...
> Other cards I have experience of (ACC X.25 card) I believe also had
> programmable vectors (yet to be confirmed) so while that mechanism certainly
> won't be in an older card like the DEUNA it is in the newer
For SIMH purposes the discussion is about DEC peripherals: for those the three
mentioned are the only ones with programmable vectors. Sure, the idea makes a
lot of sense in newer devices and it's not surprising that some non-DEC boards
would have adopted the same feature.
paul
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