[Simh] EXT : Questions regarding future simulator development

[Hittner, David T (IS)]

To answer your questions:

1> Yes, you could detach the command channel from the simulation loop by putting the command channel in a different thread. The problem then becomes one of synchronization between the two threads to do the [limited] amount of things that should be allowed while the simulation loop is still running. You would also need to put in options to enable/disable command-channel threading - some people do not want to change the removable media "on the fly", and some older host systems do not support pthreads. Someone may have already submitted this code, or it may be in the next version of SIMH (4.0), it would be best to check with Mark.

2> Assuming that the MASSBUS hardware devices actually supported the extended configuration, you could certainly add the extra components into the configuration. The question then becomes do any of the operating systems that ran on the original hardware support the extended configuration? If the operation systems don't support the extensions, then adding the extra simulated components is a waste of time. Otherwise, you just have to ask yourself "Is it worth the effort?" Note that any new components added to a simulation should be disabled by default for compatibility with older scripts.

3> Yes. There is an unreleased VAX simulator variant in the wild with 32 processor support. It would certainly be possible to run additional CPU simulator loops on other threads - you just have to add synchronization support for the system shared resources - I/O bus, system bus, memory, etc. However, in the case of the PDP 11-11/74, you have to ask yourself the question "Is it worth the effort to add multi-cpu support to more "correctly" simulate a PDP-11/74?" since the current PDP-11/70 simulation already outperforms the fastest hardware ever made. :-) Not knowing what the PDP-15 UNICHANNEL-15 is, I can't comment on it.

David Hittner

-----Original Message-----
From: simh-bounces at trailing-edge.com [mailto:simh-bounces at trailing-edge.com] On Behalf Of Christian Gauger-Cosgrove
Sent: Wednesday, April 10, 2013 12:28 PM
To: simh at trailing-edge.com
Subject: EXT :[Simh] Questions regarding future simulator development

Hello,

I have a few quick questions about what could be added to SIMH. Not that I could add the features, my skills at C are not quite excellent, so in general, I wouldn't really be able to add anything to the project... or it would be better to say, I wouldn't be able to add anything remotely competently.

Any way on to the questions! How difficult, and better to ask, how possible would it be to add the following to SIMH at some point in the future?

1. Some way of interacting with devices while the simulator is still running. What I mean would be some way of breaking to the "sim>"
prompt without halting the simulated CPU. So one could do things like swap disk packs, floppy diskettes and magnetic tapes without halting the system. Kind of like the way the Hercules emulator let's you affect the system on the fly.

2. Additional MASSBUS controllers and disks. What I mean is, since the actual PDP-11/70 could have four RH70 MASSBUS controllers installed in it, would it be possible to have another set of RP disks and TU tape drives added to SIMH? Also, would it be possible to have the RS03 and
RS04 fixed head disks added to the RP device list? I ask only of the
RS03 and RS04 because while they are not strictly necessary any more (being they were small logically, but rather quick, swap disks), it would be nice to have to be able to (re)create more "authentic"
systems.

3. Would it be at all possible for SIMH to become capable of supporting a multiprocessor system? E.g. the PDP-15's UNICHANNEL-15 option, or the PDP-11/74.


Thank you to any who answer this e-mail. I'd try my own hand at making some of the modifications to the SIMH codebase, but as I said, my skills at present are far too low to be of any real use.


Cheers,
Christian
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