[Simh] EXT :Re: Issue #731 - simh PDP11 RSX11M-PLUS Unibus 11/94 system with 2 DEUNA ethernet device XUB not working

[Paul Koning]

> On Jul 31, 2019, at 1:34 PM, Geoff Conway <gconway at 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