Real simh version

[Robert Keck]

My newly installed PiDP-11 simh version reports:

PDP-11 simulator V4.0-0 Current  REALCONS build Dec  1 2024

Yet looking at the source files in the /opt directory or in the obsolescence github repository, most of the files are clearly not up to date with either the opensimh or simh github repositories and generally seem to be years behind (more like 3.x) Am I missing something?

It seems like it would be good if obsolescense, instead of making a copy of simh, forked the opensimh repository, and then created a REALCONS branch. Then at least there would be a possibility of keeping it up to date by merging in changes.

[Johnny Billquist]

Correct the PiDP is based on a rather old version of simh V4. The whole
interfacing with the front panel is a hack that requires quite some work
to incorporate in new versions of simh, so it happens rarely that it
moves forward.

Johnny

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email: b...@softjar.se || Reading murder books
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[Robert Keck]

I've looked at it a bit now, and I can see it is something of a hack. However, most of the changes to the mainline code seem to be guarded by "#ifdef USE_REALCONS" and the changes seem to involve only a few files, so it does not appear that it should be to be too hard to keep changes merged in. Since I'm planning to try and update it to the most recent version of simh, I guess I'll find out just how hard it is.

[Robert Keck]

The other thing I just noticed is that version 4 of simh seems to be a nebulous concept. There are a couple of tags for version 4, but there are multiple tags for various 3.x versions that occur after the version 4 tags. (e.g. v4.0-Beta-1 Nov 21, 2014, v3.12-3 Jan 31, 2023)

On Friday, June 27, 2025 at 2:27:10 AM UTC-4 b...@softjar.se wrote:

[Anton Lavrentiev]

Some of the patches (esp. the critical ones) in v3, which Bob Supnik supports, get pushed to v4 (and v4.1) as well.

Also, the pidp11 fork was maintained in git here for some time, but it gets harder and harder to do because of the hackish approach with the front panel, due to accumulating conflicts:

https://github.com/desaster/simh-realcons-pdp11

so it was kinda abandoned ...

The best would be to use the native simh front panel API (which exists) instead of the sunrpc stuff, but nobody understood that so far ... That way, simh could be just built from the current sources without any forks needed.

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[Johnny Billquist]

That's because the fractured history of simh.

Bob Supnik (the original author) is still working on V3, doing new
released from time to time.

Mark Pizzalo took Bobs work, and made V4, and is continuing doing work
there.

At some point, Mark did some things that upset a lot of people, and Open
simh was forked from Mark's work, and continue doing work from there,
also called V4.

Johnny

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[Johnny Billquist]

Go ahead. There are probably several people who would be happy to have a
more up to date version of simh for their PiDP.

Be aware that you'll not get that incorporated upstream. It's a hack,
and not one that simg proper wants to see in there.

Johnny

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[John Hudak]

I am somewhat aware of the 'fractured' history. This may be a loaded question but....What version would be 'better' to use?  I guess 'better' would have to be defined: most 'correct', maintained? best coverage of DEC gear, etc. 

Thanks

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[Glenn Babecki]

So will the "real V4" please stand up...😉

Ever since I got involved with SIMH, I have been confused by the fractured history. Given what I know about the background, I have tried to focus on Open SIMH where I had a choice of platform.

That said, it appears that a lot of the PiDP projects seem to be based on the Mark Pizzalo's V4. I am with John H. on this account and interested to see where the PiDP evolution goes.

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[Robert Keck]

Thanks for all the input.

I am aware that the existing PiDP-11 stuff is a hack. On the other hand it has been a hack for many years and no one has come up with anything better. Assuming I can bring the existing hack up to the current simh version, I'll fork it, create a branch and let anyone who wants do what they will with it.

I am also aware of the API. However, I can find no documentation on it and the code is very complex. Without documentation, the only person who can probably successfully use it would be the author. It seems to be an unfortunate fact of life with open source projects, that someone will do a lot of work to implement a feature, but not provide enough documentation so anyone else can use it.

I am also aware of the unfortunate fractured history. Much as I would prefer to use FOSS software, the reality seems to be that the simh version seems to get a lot more attention than the opensimh version.

In terms of versioning, I would say that both simh and opensimh need to periodically add tags that reflect some kind of reasonable versioning. For people new to simh and PiDP-11, it exceedingly confusing to have simh code coming from multiple, often unidentified repositories, with no tag or hash identifying the version. I get that a small number of people do most of the work, and I really appreciate that. But still, it is not hard to add a tag.

[Clem Cole]

On Fri, Jun 27, 2025 at 12:05 PM Glenn Babecki <glenn....@gmail.com> wrote:

So will the "real V4" please stand up...😉

Ever since I got involved with SIMH, I have been confused by the fractured history. Given what I know about the background, I have tried to focus on Open SIMH where I had a choice of platform.

That's a good idea.

 

That said, it appears that a lot of the PiDP projects seem to be based on the Mark Pizzalo's V4.

Ah -- not really.  It's because Oscar forked >>before<< Mark took is code private and OpenSIMH had to be created.

It's not based on Mark's >>current<< code base.

This is what is confusing.

 

I am with John H. on this account and interested to see where the PiDP evolution goes.

At some point, the desire is that Oscar's code base will be  OpenSIMH mainline with a more portable (non-Hacked Real Console) front end.

There are reasons why that is not easy/possible right now.  So be patient.

Tx

Clem

[Clem Cole]

On Fri, Jun 27, 2025 at 11:37 AM John Hudak <jjh...@gmail.com> wrote:

best coverage of DEC gear, etc. 

That would be OpenSIMH. It continues to have more simulators and new support and is 100% FOSS.  That's the goal of the project and always has been.   Bob continues work in his private V3 branch and his changes are brought forward, although most new simulators have been developed in the OpenSimH V4 current branch.  He is also on the SG.

Mark maintains a private branch and offers it to people under his rules; which is fine.   Many people like it.   But it is >>not<< what is used by Oscar.  Oscar uses a >>much<< earlier fork of Mark's code when it was less restricted.

[Glenn Babecki]

Clem,

Thanks for clarifying the PiDP lineage. Full disclosure, I haven't really looked into that level of detail so my description was based on impressions I was getting from the conversation thus far.

I'm in no hurry for a full-fledge cleanup of the PiDP framework, but it would be nice to have in the not too distant(?) future.

Robert,

I'm with you on the lack of usable SIMH development documentation. I'm actually in the midst of investigating how to add a display device to the SIMH PDP-9.  The existing SIMH documentation only describes broad functional aspects of the simulator and some key data structures.  However, the documentation fails to provide any detailed description of the functional architecture let alone a how-to guide with examples.  It's not practical to reverse engineer the development guidelines from looking at many individual implementations across the simulator source.  So I'm having to resort to assistance from people in the know, and that's a crap shoot.

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[Robert Keck]

Actually I think what is confusing is that Oscar's code seems be from around March 15, 2018 before the split and after the v4.0-Beta-1 tag. But all tags after that point are version v3.x. So taking the particular case of opensimh where the most recent tag is v3.12-3, what version would one consider the head revision to be?

If there are plans to do something to improve the situation, it might be useful to let the community know what the status of that effort is, what the issues are, and who is working on it, to avoid duplication of effort. Whoever is working on it might find that there would be volunteers to help with the effort.

As far as patience goes, many of the users of PiDP11 are probably people like me who used PDP-11s when they were young, and like me, are no longer young. So there is limited time left  😉

[Clem Cole]

On Fri, Jun 27, 2025 at 12:38 PM Robert Keck <dumm...@gmail.com> wrote:

Actually I think what is confusing is that Oscar's code seems be from around March 15, 2018 before the split and after the v4.0-Beta-1 tag. But all tags after that point are version v3.x. So taking the particular case of opensimh where the most recent tag is v3.12-3, what version would one consider the head revision to be?

I just did a:

% git pull origin master 

% make

I see: .....  simulator Open SIMH V4.1-0 Current        git commit id: 29d39002

So that's the head: 

If there are plans to do something to improve the situation, it might be useful to let the community know what the status of that effort is, what the issues are, and who is working on it, to avoid duplication of effort.

Like many FOSS projects, we welcome PR submissions to OpenSIMH; the SG will review them and take them as appropriate.

 

As far as patience goes, many of the users of PiDP11 are probably people like me who used PDP-11s when they were young, and like me, are no longer young. So there is limited time left  😉

Be careful.  Many of us on the SG started programming in the 1960s (in my own case, 1967).  I think the latest member of the SG began in the early 1970s. Also remember, OpenSIMH's goals are different than Oscar's. Our work is based on some foundational principles. We strive to:

• Preserve the ability to run old/historically significant software. This means functionally accurate, sometimes bug-compatible, but not cycle-accurate, simulation.
• Make it reasonably easy to add new simulators for other hardware while leveraging common functions between the simulators.
• Exploit the software nature of simulation and make SIMH convenient for debugging a simulated system, by adding non-historical features to the environment.
• Make it convenient for users to explore old system environments, with as close to historical interfaces, by mapping them to new features that modern host operating systems provide.
• Be inclusive of people and new technology. It’s serious work, but it should be fun.

The primary directive is to correct errors when we find that the simulators do not match actual hardware behavior, which is often different from the official definition of how the hardware was intended to work.  Also remember that OpenSIMH supports an extremely wide number of systems.

OpenSIMH meets all of the goals and works fine without the 'blinkenlights" that Oscar provides, and here is lies the issue.   While the "REAL CONSOLE" is a >>nice to have<< as far as the simulator is concerned, it is not necessary.  

If at some point, someone will splice a new "real cons" into the OpenSIMH code base in a more elegant manner — i.e. one that does not mess up all the other simulators — is a tad more general in its interface.  That would be a good thing.   To do this, a number of things need to happen.  On Oscar's (the real cons) side, the client and server need to be rethought.   He originally wrote it for Raspbian, on an RPi2 using direct access to the GPIO.   The client should use the Linux gpio library and be portable to other Linux-based boards.  I >>personally<< think that were a bit more flexible in both client and server, it might make huge difference.    I've thought about how to do it and talked to Oscar a good bit about.   I have some of it working in a private sandbox, with one of my PiDP11s, but it's not there and I've been too busy with other projects to get back to it.

[Henry Bent]

I have attempted to contact Oscar about software issues repeatedly and have had no success. Is anyone on this list in contact with him?

-Henry

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[Johnny Billquist]

"Choice of platform"? All versions of simh will build on all the same
platforms, I would expect. Maybe some have created more of an automated
build system or something, but the basic code is just as portable for
all of them.

As for "real"... I guess they all are, in their own way.

Johnny

> <mailto:b...@softjar.se> wrote:
> >
> >     Correct the PiDP is based on a rather oldversion of simh

> V4. The whole
> >     interfacing with the front panel is a hack that requires
> quite some
> >     work
> >     to incorporate in new versions of simh, so it happens
> rarely that it
> >     moves forward.
> >
> >     Johnny
> >
> >     On 2025-06-26 22:25, Robert Keck wrote:
> >      > My newly installed PiDP-11 simh version reports:
> >      > PDP-11 simulator V4.0-0 Current  REALCONS build Dec  12024
> >      >

> >      > Yet looking at the source files in the/opt directory

> or in the
> >      > obsolescence github repository, most of the files are
> clearly not
> >     up to
> >      > date with either the opensimh or simh github
> repositories and
> >     generally
> >      > seem to be years behind (more like 3.x) Am I missing
> something?
> >      >
> >      > It seems like it would be good if obsolescense,
> instead of making
> >     a copy
> >      > of simh, forked the opensimh repository, and then
> created a REALCONS

> >      > branch. Then at least there would be apossibility of

> keeping it
> >     up to
> >      > date by merging in changes.
> >      >
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[Glenn Babecki]

Ha, I didn't want to be the one to play the "mortality" card, but as Clem and Robert have stated, most of us a clearly from the same era of computing given the equipment timeframe.  It certainly gives a different meaning to the phrase "in one's lifetime."

Clem,

Thanks for describing what you think needs to be done to bring the PiDP physical panel implementation into better alignment with SIMH/Open SIMH development.  I don't think anyone is poking a stick at the goals and objectives of either version of SIMH.  Clearly the PiDP development should be piggybacking on SIMH and not unduly steering it.  Anyway, looking forward to hearing more about efforts to realign the PiDP track.

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[Robert Keck]

Thanks, I'll take a look at desaster stuff.

I kind of looked at the API a while back, but it did not seem to be particularly well documented, nor did there actually seem to be an actual working example of it in use. I'll look again, but I'm wary of APIs that are fundamentally conceptual and don't have a working test example.

Irrespective of an API, there are certain changes that need to be made to the PDP11 simulation code in order to drive a front panel, if only because you need to do something about the 11/70 SHFR, which is not directly simulated and is important if the front panel is to approximate a real 11/70.

[Robert Keck]

Getting this (the version) required building the whole thing and running it.

With some grepping, I discovered the version is hard coded in sim_ref.h. Ideally, the build system should pull the revision from the last tag in the repo (and not hard code it) and then add on the git ID of the checked out version. This is how many of the open source projects I've worked with handle it. That way, you don't have to build and run the project (or know in what .h file to look) to find the corresponding version in the repo. Furthermore, this provides a history, just by looking at the repo on Github, of the significant milestones in the project.

[Anton Lavrentiev]

The hardcoded version is just to distinguish simh (4.0) and open-simh (4.1). The real version goes by the git commit id, which is obviously unique, and obviously automated, and links to the repo directly (so you know what your build is).

I would also like to correct the autocorrect in my previous post. While talking about the simh front panel API, it appears that I said "nobody understood", but that was autocorrect from what I wanted to say, "nobody undertook" the effort of using it for PiDP11.

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[Mark Pizzolato - Info Comm]

Both the simh and the open-simh codebases explicitly provide the commit id at build time and display it both at startup and in the "SHOW VERSION" output.  Extracting a zip from either repo saved the relevant commit id in the include file.

Apart from this, when Oscar started his various front panel efforts, he didn't ask me or the group for advice and went down the path you have today.  When he started, the simh codebase already had a provision to facilitate front panel solutions (either hardware or virtual software ones).  This facility is called the front panel API.  It is built into every simh simulator such that the simulators built already can be driven in the traditional way OR from an external front panel application.  Such an application can interface a GUI or actual hardware.  The only piece which needs any host platform specific code is the front panel application.  

When Oscar released his first front panel system I pointed out the front panel API option and since he already had something that worked for him he kept with it and then continued that for each of the subsequent PiDP solutions.

His approach deliberately didn't get into the simh codebase since it tangled host platform code into the SCP and the simulator code.

It would seem that REALCONS could be reworked to leverage the simh front panel API.  I'll be glad to work with someone interested in digging into that idea.

- Mark

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[Johnny Billquist]

I probably should say that Oscar didn't write the front panel code, and
neither did it originate with the PiDP.
This is work that (as far as I can remember) originates with Joerg Hoppe
and the blinkenbone project, where he wanted to interface a real
PDP-11/70 front panel with simh.

Oscar basically just borrowed/carried over the blinkenbone bits into
PiDP. Oscar isn't really a programmer, and happy admits as much if you
talk to him. He just enjoys doing these things, and getting things
working, but he's depending on others for much of the software bits.

And also, if I remember right, the blinkebone thing was done before
there was any API for front panel stuff in simh. But with that said, the
way the things are done (basically faking/injecting things via the user
interface, and all kind of hacks) is pretty horrible.

Johnny

> SG will review themand take them as appropriate.

>
>
> As far as patience goes, many of the users of PiDP11 are
> probably people like me who used PDP-11s when they were young,
> and like me, are no longer young. So there is limited time left  😉
>
> Be careful.  Many of us on the SG started programming in the 1960s
> (in my own case, 1967).  I think the latest member of the SG began
> in the early 1970s. Also remember, OpenSIMH's goals are different
> than Oscar's. Our work is based on some foundational principles. We
> strive to:
>

> * Preserve the ability to run old/historically significant

> software. This means functionally accurate, sometimes bug-
> compatible, but not cycle-accurate, simulation.

> * Make it reasonably easy to add new simulators for other hardware

> while leveraging common functions between the simulators.

> * Exploit the software nature of simulation and make SIMH

> convenient for debugging a simulated system, by adding non-
> historical features to the environment.

> * Make it convenient for users to explore old system environments,

> with as close to historical interfaces, by mapping them to new
> features that modern host operating systems provide.

> * Be inclusive of people and new technology. It’s seriouswork,

> but it should be fun.
>
> The primary directive is to correct errors when we find that the
> simulators do not match actual hardware behavior, which is often
> different from the official definition of how the hardware was
> intended to work.  Also remember that OpenSIMH supports an extremely
> wide number of systems.
>
> OpenSIMH meets all of the goals and works fine without the
> 'blinkenlights" that Oscar provides, and here is lies the issue.
>  While the "REAL CONSOLE" is a >>nice to have<< as far as the
> simulator is concerned, it is not necessary.
>
> If at some point, someone will splice a new "real cons" into the

> OpenSIMH code base in a more elegant manner —/i.e/. one that does

> not mess up all the other simulators — is a tad more general in its
> interface.  That would be a good thing.   To do this, a number of
> things need to happen.  On Oscar's (the real cons) side, the client
> and server need to be rethought.   He originally wrote itfor
> Raspbian, on an RPi2 using direct access to the GPIO.   The client
> should use the Linux gpio library and be portable to other Linux-
> based boards.  I >>personally<< think that were a bit more flexible
> in both client and server, it might make huge difference.    I've
> thought about how to do it and talked to Oscar a good bit about.   I
> have some of it working in a private sandbox, with one of my
> PiDP11s, but it's not there and I've been too busy with other
> projects to get back to it.
>
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[Chuck McManis]

I was going to echo a bit what Johnny said, but I make the observation that simh emulates lots of different architectures, whereas the PiDP-11 really only emulates variants of "one" architecture (and not all variants). I think an argument could be made to pull PDP-11 emulation *out* of simh into its own standalone service with the front panel interfacing built-in as the "product software" for this specific product. That package would not need to track changes in simh, and would be consistent from release to release.

--Chuck

On Fri, Jun 27, 2025 at 1:36 PM Johnny Billquist <b...@softjar.se> wrote:

I probably should say that Oscar didn't write the front panel code, and
neither did it originate with the PiDP.
This is work that (as far as I can remember) originates with Joerg Hoppe
and the blinkenbone project, where he wanted to interface a real
PDP-11/70 front panel with simh.

3a3661%40softjar.se.

[Johnny Billquist]

Why would simh do such a thing just because someone else made a system
based on simh?

Johnny

> 3a3661%40softjar.se <https://groups.google.com/d/msgid/
> pidp-11/4fd3a9e9-8fd1-4915-8504-2066a03a3661%40softjar.se>.

>
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[Robert Keck]

Mark:

I now see the commit ID is included. But for new users, the fact that is also prints out a Vx.x version, it is confusing. I would suggest if people are going to use the commit id to identify the version then the Vx.x be removed and the commit ID be made prominent. If people want a Vx.x type string as well, I would suggest that it comes from a tag. (Only a suggestion, since I'm not in the position to make it happen).

As far as the API goes, I would be interested in giving it a shot, if you can provide some guidance. I will start by taking a look at the frontpanel test code and see if I can figure out how to then write a simple console application which uses the API with the PDP-11 as opposed to a VAX. I suspect I will need to call on you to answer the inevitable questions.

Johnny (in reply to Chuck):

I don't think he is saying simh should do this. Rather the PiDP-11 enthusiasts might want to proceed in this way (I don't know that I necessarily agree, but...)

This discussion group is actually a PiDP-11 discussion group, not a simh discussion group (there is another group for that) and the interests of the two groups, while they certainly overlap are not necessarily identical. So I think the various keepers of the simh versions should be careful not to assume that the comments here imply that it is your job to accommodate PiDP-11. Certainly for me, I'm trying to figure out how to use the most recent versions of simh as it stands with my PiDP-11 front panel with a reasonable effort. I have no particular affection for the way REALCONS works, so I'm very open to doing things another way. In fact, my preferred way of using it would be to run simh on a Beagle-V Fire, which includes an FPGA. That way the FPGA could drive the front panel with 0 demand on the RISC-V processor running simh.

[terry-...@glaver.org]

I posted a long, well-thought-out (IMHO) reply to this post, which now shows as "Message has been deleted". I did not save a copy because I wasn't expecting it to be shredded.

This was likely Google running amok. Perhaps the group admin(s) could look into disabling that "feature", and reinstate my post. I know we've had this problem in some other Google groups over the years.

OTOH, if the removal was a manual intervention, I would like the responsible party to stand up and justify their action.

[Michael J. Kupec]

Terry,

When did you do that long post? 

Some of us are email packrats and odds are, some of us may have that post archived offline. 

Or are you saying the admins deleted it shortly after you sent it out? (Granted, being a SNMP email, it is kind of hard to do a message recall!)

Have a great Day!

Michael J Kupec 

Sent from my iPhone

On Jun 27, 2025, at 7:06 PM, terry-...@glaver.org <terry-...@glaver.org> wrote:

I posted a long, well-thought-out (IMHO) reply to this post, which now shows as "Message has been deleted". I did not save a copy because I wasn't expecting it to be shredded.

This was likely Google running amok. Perhaps the group admin(s) could look into disabling that "feature", and reinstate my post. I know we've had this problem in some other Google groups over the years.

OTOH, if the removal was a manual intervention, I would like the responsible party to stand up and justify their action.

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[John H. Reinhardt]

On 6/27/2025 6:31 PM, Michael J. Kupec wrote:

Terry,

When did you do that long post? 

Some of us are email packrats and odds are, some of us may have that post archived offline. 

Or are you saying the admins deleted it shortly after you sent it out? (Granted, being a SNMP email, it is kind of hard to do a message recall!)

Have a great Day!

Michael J Kupec 

Sent from my iPhone

On Jun 27, 2025, at 7:06 PM, terry-...@glaver.org <terry-...@glaver.org> wrote:

I posted a long, well-thought-out (IMHO) reply to this post, which now shows as "Message has been deleted". I did not save a copy because I wasn't expecting it to be shredded.

This was likely Google running amok. Perhaps the group admin(s) could look into disabling that "feature", and reinstate my post. I know we've had this problem in some other Google groups over the years.

OTOH, if the removal was a manual intervention, I would like the responsible party to stand up and justify their action. --

Terri,
  I'd lay odds on it being some sort of Google Groups glitch.  The only admin for this group that I know of is Oscar and I can't see him deleting anything.  Between the brain fog he's been dealing with and working on PiDP projects, he's not often here.  I get my messages via email and keep all of them except for the period a while ago when Google Groups was overwhelmed by spam (mostly the USENET groups but also this one and others) and have not seen anything from you since the other day about the knobs.

-- 
John H. Reinhardt

[terry-...@glaver.org]

On Friday, June 27, 2025 at 7:32:00 PM UTC-4 michae...@gmail.com wrote:

Terry,

When did you do that long post? 

Some of us are email packrats and odds are, some of us may have that post archived offline. 

Or are you saying the admins deleted it shortly after you sent it out? (Granted, being a SNMP email, it is kind of hard to do a message recall!)

I posted it via the Google Groups web UI: https://groups.google.com/g/pidp-11
 

[terry-...@glaver.org]

On Friday, June 27, 2025 at 7:54:48 PM UTC-4 John H. Reinhardt wrote:

  I'd lay odds on it being some sort of Google Groups glitch.  The only admin for this group that I know of is Oscar and I can't see him deleting anything.

 The Google Groups UI runs amok occasionally. We had a group where every post, even from the group creator and moderators, was being auto-deleted.

  Pretty much anything involving the web is being "infused with AI" and having pointless UI rearrangements done (to the point where Firefox's help has to ask you what version you're running) because almost all useful features the developers were willing to implement have been done, so now they're just rearranging the deck chairs.

[John H. Reinhardt]

Change for the sake of change.... The bane of productivity.

-- 
John H. Reinhardt