On 2018-04-10 01:55, Paul Koning wrote:


On Apr 9, 2018, at 6:25 PM, Mark Pizzolato <m...@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: b...@softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol
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