On 2018-04-10 10:26, Mark Pizzolato wrote:
On Monday, April 9, 2018 at 11:51 PM, Johnny Billquist wrote:
On 2018-04-10 00:25, Mark Pizzolato wrote:
On Monday, April 9, 2018 at 3:08 PM, Johnny Billquist wrote:
On 2018-04-09 22:16, Mark Pizzolato wrote:
On Monday, April 9, 2018 at 11:57 AM, Johnny Billquist wrote:
For serial ports, that
obviously means that you might connect one line to a physical line,
another to a telnet listener, and another one not connected to anything
at all.

You can actually do that right now.  Each line on any multiplexer
device can have a separate TCP listener or be connected to a remote
TCP port or to a local serial port, or be part of the pool of ports
which may optionally be configured to listen for the mux device.

Right. But I cannot skip a few lines. And simh really dislikes me if the
number is
not a multiple of 8.

Once the Qbus 4 vs 8 ports for the Qbus DZV11 bug that Bob pointed
out is fixed, you certainly can skip as many lines as you want.  Simh
is simulating the hardware.  You couldn't buy a 2 port DZ11.  They all
had 8 ports.  You can choose to connect as many or as few of these
lines to wherever you want with the current implementation and
have the others either be completely disconnected/unused or
generically listening on a specific TCP port.

So how do I disable (not connect) some lines in simh?

You don't disable lines.  You merely describe which ports you want to connect 
to where and leave the others alone.  Check:

     sim> HELP DZ ATTACH

and look for how you might explicitly configure one line separately and keep on 
going for each line you want to connect somewhere.  Lines you don't describe 
connections for won't be used unless you give the whole mux a listen port (like 
things worked in the original simh mux behaviors).  The whole mux listen port 
is optional.

Ok. So if I were just to leave them alone, I'd be good. Excellent.

FYI, you can now configure the DZ device on Qbus PDP11's with any multiple of 4 
lines and get the correct number of controllers with all of the specified lines 
potentially connected in the various allowed ways.  Changing the CPU type from 
a Qbus one to a Unibus one might add 4 additional lines to the setup if (lines 
% 8) isn't 0.

Yeah, that make sense.

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.

...which I can with real hardware.

See prior message about rewriting many things in your spare time.


And exactly
how many units/lines the controller have should also be a factor here

This also comes back to disks, where I might not want to configure
four disks on one controller, but maybe one controller per disk.

The device simulation for DEC's disk controllers usually default to
the maximum number of disk devices each controller was capable of
Each of those device units can be disabled so if you want one
controller per disk, you absolutely can.

Up to 4 separate MSCP controllers can be configured today (with up to
16 separate drives).  A single RP controller with up to 8 drives is available.

This functionality has solved most user problems without issue.  If
you've got a simulation need for more than this, you can extend or
rewrite what's there now.  Since configurations that can be simulated
today can far exceed what was ever possible on any real system, it
seems like a lot of work to address the theoretical flexibility you're
asking for.  :-)

I'd like to have more than 4 disks on one MSCP controller. There is
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.

The CMD SCSI controller, for example. I can have as much as 7 disks on
one controller there. Or 7 tapes. And that exists for both Unibus and
Qbus, and I happen to have both. But why do you want to have a
limitation in simh at all here?

It isn't a design to be limiting.  We've merely got simulations of real DEC
hardware connected to simulated DEC systems.  I don't think we've got any 
Unibus, Qbus or Massbus device simulations which simulate other that DEC built 

That might be, but you also impose some artificial limitations...

The MSCP was designed to explicitly not
have such limitations in the architecture. And while I'm at it, it would
be nice (although this is just cosmetic) to be able to set the disk
identifier to any string, and not have my arbitrary sized disk always be
identified as an RA81.

The disk Media ID is encoded in a 32bit value.  I'm not sure what the encoding 

That's been documented in some manual. I know I've seen it, and I can dig it up for you. But essentially, it codes in (I think) up to three letters, followed by a number.

Some OSes leverage the encoded value to correspond specifically with a 
particular model of DEC disk and run from there potentially presuming details 
about disk size or geometry.

I certainly hope not. Like I said, this is cosmetic. MSCP reports disk size directly, and the id is just for information. Anything that is mad enough to assume size based on the id instead of the size reported by the device would be some seriously broken software.

The arbitrary sized disk actually uses the RA82 encoded value for its Media ID. 
 This is ONLY when the disk is created.  When a disk is subsequently attached, 
whatever drive type is either default OR explicitly specified with a SET RQn 
RA90 (or one of the many other choices in the list) is what the drive type ends 
up as when the media id is passed to the OS.  Current Simh RQ devices autosize 
and don't worry about the default size that a particular drive type originally 
started as.

Like I said, this is cosmetic. It just looks very silly to have a disk reported as being an RA81 (or whatever) when the disk is in fact no such thing. And since the ID can contain any kind of name within the limitations on such names, there isn't really a good reason why it would be limited to such a small set as it currently is.

And that limitation of 7 is obviously because of limitations on SCSI,
which can only have 8 devices on the bus, and the controller is one.

Well, DEC never made an MSCP disk controller which connected SCSI disks, so 
even though as you point out there being 12bit values for unit settings in some 
drives and the MSCP protocol could clearly handle relatively arbitrary unit 
numbers, you couldn't buy a DEC controller with more than 4 drives.

Of course DEC did. It's called the RQZX1. Qbus MSCP controller using SCSI.
However, I can't remember offhand if that model supported more than four disks. I have one of them somewhere, along with the manual. But not near at hand. But my point was/is that MSCP was designed to explicitly avoid such silly limitations. An MSCP controller can support any number of disks. The actual UDA50 and KDA50 only had four connectors for disks, which is the reason for that limit. Other controllers could just as well have a different number. From a programming point of view, it would be no difference. That's one of all the nice things about MSCP.

So we are artificially limiting ourself to four disks because some DEC controllers only had four connectors. The MSCP protocol have no such limit, and neither does the software. You can without problem generate an RSX system where you have 16 disks on one MSCP controller, if you want to.

As it turns out, in the PDP11 simulator, device RQ has 4 units which start at 
0.  Device RQB has 4 units (RQB0, RQB1, RQB2 and RQB3) which have unique MSCP 
unit numbers (4, 5, 6 and 7). Device RQC has 4 units (RQC0, RQC1, RQC2 and 
RQC3) which have unique MSCP unit numbers (8, 9, 10 and 11). Device RQD has 4 
units (RQD0, RQD1, RQD2 and RQD3) which have unique MSCP unit numbers (12, 13, 
14 and 15).

So, you've already got up to 16 MSCP disks each with unique unit numbers.

Right. But there is a difference between having one controller, and having four. In RSX it makes an important difference in that each controller configured takes pool space, of which there is a limited amount. So there is a real, tangible benefit in having more disks on the same controller here.

Each of these disks can be up to just under 2TB in size.

More than enough for RSX, where the current limit is 8G for one disk. :-)

If you really need more than that you can use up to 8 RP07's and all the other 
supported disk types as well.

It's not so much about disk size. We can obviously fit more than enough disk space on a simulated system to go far beyond what anyone ever used in real life. However, there are more aspects that can be relevant here, such as my point about memory usage inside the simulated system. Others might have other ideas or reasons...

And the limitation in this case do not seem to make much sense. Just as it don't make much sense that we have a limit of 8 RP07 drives. A PDP-11/70 can have four RH70 controllers, and each one of them could have 8 RP07 disks.

Have fun.

Always. :-)


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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