[Simh] DZ11 vs DZV/DZQ11

[Johnny Billquist]

On 2018-04-10 03:28, Mark Pizzolato wrote:
> On Monday, April 9, 2018 at 4:56 PM, Paul Koning wrote:
>>> On Apr 9, 2018, at 6:25 PM, Mark Pizzolato <Mark at infocomm.com> wrote:
>>>
>>> ...
>>>> ...
>>>> 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.
> 
> I see 2 approaches to adding support for different unit numbers:
> 1) A unit number is settable uniquely for each of the 4 drives that can be
> attached to any of these controllers.  This would map to a conceptual Drive Unit
> Plug.  Did these exist on DEC MSCP drives?

Yes they did.

> 2) A 'base' unit number can be set on a controller and each drive on that controller
> would then have unit numbers equal to the base plus their existing internal unit
> numbers.  This may have been how third party MSCP controllers worked.

I've never seen any controller doing this approach.
The SCSI controllers I've seen and used have a configuration tool built 
in, which allows me to map the SCSI unit number to an arbitrary MSCP 
unit number for each unit.

> Which of these best reflects how the real hardware worked?

I'd say option 1.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
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