[Simh] DZ11 vs DZV/DZQ11

[Johnny Billquist]

On 2018-04-10 01:55, Paul Koning wrote:
> 
> 
>> On Apr 9, 2018, at 6:25 PM, Mark Pizzolato <Mark at infocomm.com> wrote:
>>
>> ...
>> With simh as it is currently written, all of your DZ devices do need to
>> be configured to have adjacent CSR address blocks and Vectors.
>> They can't separately be scattered around the I/O space.
> 
> That conforms to the float rules, so it seems like a reasonable restriction.  It's theoretically possible to configure real hardware differently, and in some OS you can then still talk to the devices (by setting addresses manually) but it would not be a standard config and probably not supported.

While RSX certainly tries to probe CSRs and vectors according to the 
configuration rules DEC defined, in my experience, most machines never 
followed those rules. People just did not understand them enough, nor 
did they ever go and change a bunch of controllers whenever some device 
was added or removed.
So in real life, I'd say almost every machine always had other layouts 
of CSRs and vectors than the recommended one, and atleast with RSX, you 
always run a SYSGEN, and have to at put in the CSR and vector manually 
anyhow. The only time autoconfiguration was done was at the initial 
install of the system. And later reconfiguration was totally manual.

>>> ...
>>> I'd like to have more than 4 disks on one MSCP controller. There is absolutely
>>> no reason for the limit of 4. That's just an implementation detail on some of
>>> the existing MSCP controllers, but there are MSCP controllers who also take
>>> more than 4 disks.
>>>
>>> And that exists in real life, and I cannot do that (and a bunch of other
>>> setups) in simh, so I'd say that simh is rather more limited than real life. :-)
>>>
>>> Same story for TMSCP.
>>
>> Please identify Qbus or Unibus controllers that had hardware support for
>> connection of more than 4 units and I'll include those controllers (with
>> their limits) in the simulator.  A pointer to the documentation for these
>> devices would be helpful.
> 
> I don't remember controllers with more than 4 units per device, but MSCP unit numbers are arbitrary 8 bit values.  So a limit of 4 units is proper, but a limitation on those unit numbers being 0..3 is not accurate.  It matters in some OS.  For example, VMS has type/controller/unit addressing (DUA3 etc.) but RSTS does not.  So on RSTS, if you have more than one MSCP controller, they must have disjoint unit numbers.  Since the unit numbers are 8 bits, that's easy to do.  But I don't see how I can do that in SIMH.

It's actually 12 bits for unit numbers. Early disks with plugs could 
only code 8 bits, but later ones, like the RA7x series use all 12, and 
have a small display where you can set the unit number.

And yes, you bring up another good point here. Forcing the unit numbers 
to be 0..3 on each controller is also a bit confusing compared to real 
life. In RSX, the unit numbers on the devices are disjunct from the unit 
numbers in the system, but it usually was good practice to keep them the 
same, otherwise it can be a bit of an hassle to figure out which disk is 
DU0: (having three disks all with unit #0 makes it really hard).
Even in VMS, it does become tricky, since there is no obvious way to 
tell on which controller the disk is, so DUA0:, DUB0: or DUC0: will all 
look the same until you've traced all the cables and controllers... Ugh!

As for more than 4 disks on a controller, I already answered that one, 
but the SCSI controllers I know will allow more than 4 disks, for example.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol