Want to run "Headless" using physical serial ports

[John]

 Ok now that my self-inflicted SIMH Drama has been resolved, I'd like to understand a little better how to congure my PiDP to be as 'realistic' as possible.

To that end I've gotten the USB-to-serial converters, and populated the two RS232 converter chips.

I'd like, initially, to have a physical terminal connected to a port - with the System configured so that at power-on, it may (or may not) require some toggle switching, but at some point the seleced OS signs on to the Terminal.  (In lieu of a real VT100, I have a Legacy Pixels adapter that has an HDMI socket and a keyboard socket, and which looks like a VT102 to the Host) [VT100s are heavy and pricey - and I've had a dozen of them at verious times...]

Then I can do stuff on the system. Like play with RT11 BASIC...  I also at some point want to get a line printer of some ilk - I've had LA120s but that's not in the cards - I have a couple of ASR33s lurking, but once again: space, noise, and maintenance.  But I would like to have "user" ports available, if only to connect outboard computers running Moba or some other serial terminal program, to simulate 'USERs'

But the goal is to have an emulation of a 'real' 11/70 - no wifi, no ethernet, only hardwired comms.

How would the PI / simh / etc be configured to untilize only the serial ports?

I'd be happy to provide an email address to take this offline, but then again I'm probably not the only person who wants to do this - or perhaps there is someone who has done it already and can say: "well, using the simple assembler, write and compile the following 2756 lines of code and debug as required. Then, download and run these 17 sequential patches and..." 

 

;}

Thanks!

Cheers

John

[Mark Williams]

wow thanks John...a man after my own heart! I was about to quit after the previous email series thinking I am blindsided with all the OS and system jargon. I too are interested in writing apps for Basic (Macro11 and C) with the minimum of system calls required. I do note that this forum covers largely system utilities programming and configuring and not much on actual applications programming on the Pidp11. I also have an interest in programming the Pis peripheral I/O one day.

Note to others: is this the right/best forum  for applications programming?

(minority) Mark 🤠

I too would like to receive responses to this query.

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[Neal G.]

There are a few things to consider in setting up "headless" operation.

The SimH configuration file, typically "boot.ini", can be revised to redirect the simulated console adapter to a physical serial port or telnet connection from a remote system. The SimH configuration can also be revised to route the additional simulated serial adapters to physical serial ports or telnet connections from a remote system.

At the SimH prompt type "help set console" and "help dz" or "help vh" for details.

The thing to consider is that you will often need access to the SImH command interface. It is used to control the physical aspects of the simulation. For example, if you need to mount a simulated tape, removable disk, paper tape, or capture the output of the simulated line printer. Redirecting the SimH command interface to a physical serial port is more difficult.

Instead, my "headless" PiDP-11 setup places the Pi on my local network via WiFi. This allows easy access to the SimH command interface through SSH or VNC.

So although in theory it might seem viable to setup your PiDP-11 for hardware only connections. Having the Pi accessible on the local network is extremely useful.

In addition to accessing the SimH command interface the WiFi connection to the Pi also makes it easy to support multi-user access through the simulated serial connections over telnet.

In my setup SimH is aware of the network to make the simulated serial connections available, but the simulated OS is unaware of the network. RSX, RSTS/E, 211BSD, RT11, and others all believe they are on hardware with no network.

- Neal G.

On Wednesday, May 21, 2025 at 10:35:59 PM UTC-5 j343...@gmail.com wrote:

 ...

[Neal G.]

My impression is that this forum is open to most anything related the PiDP-11 and general DEC-related topics.

There have been threads in the past related to getting started with Macro-11, PDP C, etc.; so if you have specific questions I am certain someone will answer  or redirect you a better resource.

I think you do not see so much "application programming" discussion because interests are so varied. For example there were previous discussions on how to build and utilize the Tektronix PLOT10 library for data visualization using a Tek4014 graphics terminal (or emulation alternatives). But not everyone is into that, data analysis and visualization on legacy systems.

Also, there is a large library of existing applications available in the old DEC user group (DECUS) archives.

New application development, at least for me, is focused more on understanding the problems developers faced back in the day;  limited memory, limited storage, lack of an IDE, and working with languages like old FORTRAN that have none of the type safety or string handling capabilities that are now taken for granted.

- Neal G.

[sunnybo...@gmail.com]

Indeed! I spent several months playing with my PiDP8 after I built it - compiling and running all my old Engineering FORTRAN programs to run under that OS. I did the same again after I built my PiDP11, though that was a bit easier having done it once.

I also spent a lot of time converting my FORTRAN Engineering programs to PL/1 (had to learn/use that in my first job after school in 1980) on a Z80 single board computer running CP/M off a compact flash card "hdd". Loads of fun. Did the same again with the the various Z80 emulators (Altair & Imsai), then again with the RC2014 Z80 system. Always fun.

I also did a lot with applications (converted from FORTRAN to C back before 2000 when I started using C for everything) on the PiDP11 running BSD 2.11 which was one of my favorite operating systems.

But it really becomes one person's fun and (dare I say) obsession. Unless you were doing similar type programming, it doesn't really translate to other people. The OS people had far more fun mostly because the OS is the OS - if you get into that then it's nearly the same for all enthusiasts of whichever OS you use. I can appreciate the OS people but was never one of them  - I was an application programmer from 1979 and that's pretty much where I remain. Too much fun stuff to do in the application arena for me to switch at this point. 

[terry-...@glaver.org]

On Wednesday, May 21, 2025 at 11:35:59 PM UTC-4 j343...@gmail.com wrote:

 Ok now that my self-inflicted SIMH Drama has been resolved, I'd like to understand a little better how to congure my PiDP to be as 'realistic' as possible.

To that end I've gotten the USB-to-serial converters, and populated the two RS232 converter chips.

One part is easy, one part less so. The "user" terminals of the multi-user operating systems (the Unixes, RSX-11*, RSTS/E, probably others) were typically connected via multiplexors on real PDP-11 hardware. The DZ-11 was the cheap one, the DH-11 was the better one. Fortunately, both are emulated in simh.

You use one to four USB-to-serial adapters plugged into the Pi's USB ports, cable them through the MAX232s and add the desired connectors to the back panel.

Once you have the connectors plugged into the Pi, they should show up as /dev/ttyUSB# devices (the # will be the port number). Fortunately, the Raspberry Pi OS leaves those ports unconfigured, which makes it easy to allocate them to simh and pass them through to the PDP-11 operating system. For example:

; Set up the USB-to-serial ports on the RPi
set vh lines=16
set vh dhu
set vh nomodem
set vh enable
;
; Note that these are "shuffled" so the cabling matches the panel
attach vh line=0,connect=/dev/ttyUSB3
attach vh line=1,connect=/dev/ttyUSB1
attach vh line=2,connect=/dev/ttyUSB0
attach vh line=3,connect=/dev/ttyUSB2

If your preferred OS doesn't support the DHU11 multiplexor, you can always fall back to good old DZ11.

You can also get fancy and have the ports that don't come out on physical connectors be available via Telnet.

The attached pictures show the internal wiring as well as the external ports (Note: DB-25 male connectors with posts were the DEC standard, and you can plug in any DEC terminal using its supplied cable without needing null modems, gender changers, etc.).

You may need to configure the serial ports in your operating system. Fancy stuff like autobaud and BREAK support will likely not work completely - there's just too many layers of emulation going on, and the PDP-11 operating systems rely on specific behavior of the multiplexors. RSTS/E 10.1 will autobaud at some speeds and not others. Frankly, I'm surprised it works at all.

The harder part is getting the "system console" (and likely the only terminal in operating systems like RT-11) onto a real serial port. There's some provisions for wiring that up in the PiDP-11 build instructions, but I've never investigated it - I'm happy with the operating system running in a terminal window on the Raspberry Pi desktop, which I access via VNC. So advice on doing that will need to come from someone else. Note that there are disadvantages to putting the system console on a physical serial port - you won't be able to use the fancy emulation available via the PI, simh, and the PiDP-11. For example, no Tektronix graphics support.

[Johnny Billquist]

The console terminal is no different than any other. Physical wiring and
so on is exactly the same as any other port. You wire things up, and you
end up with a terminal port on the Pi.

It's just that you then attach your console serial line to that one,
instead a DHU-11 or DZ-11. The syntax is slightly different, that's all.

You do:

SET CONSOLE SERIAL=...

or

SET CONSOLE TELNET=...

instead of the attach commands.

Johnny

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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

[Clem Cole]

On Sun, May 25, 2025 at 3:11 AM terry-...@glaver.org <terry-...@glaver.org> wrote:

The DZ-11 was the cheap one, the DH-11 was the better one. Fortunately, both are emulated in simh.

Ouch... 

Not quite right -- there where 3, you are correct that the DH11 (which came first in which came with the 11/20)  - was the best but it was MSI/TTL and took a full "system unit" in a BA box for 16 lines), the next in '76 was the 8 line DZ11 which took a single hex card for 8 ports, finally in the early mid 1980s, the DHV11/DHU11.  OpenSimh does not support the DH11, which is a shame and its on my TODO list to add it, because early UNIX through BSD 4.2 all assume it's the terminal MUX of choice (actually we used to use after market one made by Able computer called the DMAX DH/DM - which ran the bulk of the UUCP/USENET network back in the day),

2.11BSD knows about the DHU/DHV, but none of the earlier UNIX releases support it.  That said, it should be fairly easy to move that driver back to V7 without too much work, and probably V5 and V6 (or the Vax for that matter).  Which might be easier than adding support to OpenSIMH.

ᐧ

[terry-...@glaver.org]

On Sunday, May 25, 2025 at 6:08:56 AM UTC-4 b...@softjar.se wrote:

The console terminal is no different than any other. Physical wiring and
so on is exactly the same as any other port. You wire things up, and you
end up with a terminal port on the Pi.

 [...]

SET CONSOLE SERIAL=...

True, but that gets you the OS console port on a serial line. You still

have to control simh in a Pi terminal window. If your OS shutdown ends

with a HALT instruction, you need to go back to the Pi to do anything.

I was referring to the (presumed) ability to have the Pi itself run using

a serial port instead of the built-in graphics (or at least have a Linux

shell on the serial port and still use the graphics as an optional dis-

play).  I believe that at least on older models this is on the GPIO pins,

which may be what the PiDP-11's "serial console" header connects to.

That way you'd have simh itself running on the console serial port,

and we can treat it as a very fancy M9312 bootstrap card.

[terry-...@glaver.org]

On Sunday, May 25, 2025 at 9:26:31 AM UTC-4 cl...@ccc.com wrote:

On Sun, May 25, 2025 at 3:11 AM terry-...@glaver.org <terry-...@glaver.org> wrote:

The DZ-11 was the cheap one, the DH-11 was the better one. Fortunately, both are emulated in simh.

Ouch... 

Sorry if you had something to do with the design of the DZ11. It does smack of the 

"We have to sell this as a timesharing system, so what's the least we can get away

with doing?" It's pretty much all the joy of 8 DL11s stuck together on a board, with the

added pleasure of "which port is that interrupt for?"

This wasn't limited to multiplexors. The RB730 was the disk equivalent - "We have to

sell this VAX with disk storage and a way to back it up, what's the cheapest thing we

can come up with?" and you get the RB730 which talks to only one R80 (not RM80,

not RA80, just R80) and only one RL02.

Not quite right -- there where 3, you are correct that the DH11 (which came first in which came with the 11/20)  - was the best but it was MSI/TTL and took a full "system unit" in a BA box for 16 lines), the next in '76 was the 8 line DZ11 which took a single hex card for 8 ports, finally in the early mid 1980s, the DHV11/DHU11.  OpenSimh does not support the DH11, which is a shame and its on my TODO list to add it, because early UNIX through BSD 4.2 all assume it's the terminal MUX of choice (actually we used to use after market one made by Able computer called the DMAX DH/DM - which ran the bulk of the UUCP/USENET network back in the day),

I looked an an original DH11 and "ran away screaming" - but that was substantially later

(1982-ish). Having designed 8-port multiplexors with FIFOs and shared memory (instead

of DMA) on an S-100 card by then, the low density and high complexity of the DH11 ap-

peared to be incredibly primitive. But the technology had advanced by orders of magni-

tued in the intervening years.

I ran some Emulex DH emulators on some of my systems. IIRC, each distribution panel

was "smart" and just made more ports appear on the host adapter board.

You're correct that the DHU/DHV require rather different drivers that the original DH11 -

I wasn't aware of that - I figured they were single-board shrinks of the DH11 like the

clones. I guess DEC took the opportunity to eliminate some of the DH11 quirks like the

silo alarm and changed the driver interface.

I have a Camintonn DHV11 clone (8 ports on a dual Q-bus card) in my BA123 11/93

system, so I gravitated toward the DHU11 as the emulated multiplexor of choice in the

version of simh that the PiDP-11 runs. As I understand it, the Blinkenbone mods can't

be accepted upstream, so PiDP-11 owners are stuck with that version (or doing a lot

of work to get them into their own fork of Open-Simh).

Once you get into VAX space, all sorts of odd multiplexors appear - the DMF32 is quite

nice as a multifunction board (8 serial ports, an LP11 port, and a synchronous port

that often served as a BITNET link). I assume the reason it never got drivers for any

PDP-11 operating systems was simply that by the time it came out,  most development

was for VAX and the PDP-11 operating systems were slowly at the start of "maintenance

mode". Although maybe there is something VAX-specific to the hardware.

The DMZ32 is a true oddball - what we have there is a mostly (but not completely) func-

tional T1 controller re-purposed as a multiplexor. Transformer-coupled at both ends,

with a powered distribution panel that can be located up to a mile away using 2-pair

cable. Excellent for environments like factories where the computer room is some dis-

tance away from where the serial ports are needed, with complete isolation between

the two.

ᐧ

[Johnny Billquist]

Ok. Fair point. I was just assuming you were talking about the serial
console of the PDP-11.

simh itself is a different story, and it will always remain on whatever
terminal it was started at. If you have a serial port setup to talk with
the rpi, you can just log in there, and then start simh there, and
you'll be in the state you're talking about.

Johnny

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[Johnny Billquist]

Agreed that the DH11 is a bit much. I found the DHU/DHV nicer, in fact.
But considering the time frame, I think the DH11 was quite a nice piece
of engineering. But it's way old and large. 3rd party compatibles were
good alternatives.

The DZ11 is a bit better than just 8 DL11 stuck together. Primarily
because it at least have a (somewhat) deep fifo, while the DL11 just
have a 1 byte buffer. Easy to overflow that thing... But otherwise, the
DZ11 is something to avoid.

I also found the DMF32 a rather nice and interesting piece of hardware.
I would think it should be fairly straight forward to get running on a
PDP-11, but as far as I know, no drivers were ever written. I could be
tempted into writing some, if I got one. The only one I have access to
sits inside a VAX-8650...

Admittedly, at the moment I don't even have any Unibus -11 up and
running, so nothing would happen in near time anyway.

I'll skip commenting on the DMZ32. :-)

Johnny

> marketone made by Able computer called the DMAX DH/DM - which ran

> ᐧ

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