Re: [pidp8] OS/8 Hangs

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Steve Tockey

Sep 23, 2022, 5:51:15 PM9/23/22
to Andrew Herbert, PiDP-8

It sounds likely that the disk got corrupted, but it depends on whether that corruption is at the OS/8 level or at the Raspbian file system level. In other words, it could be a problem in a simulated block (e.g., the boot block) in an otherwise good Raspbian file. Or, it could be that the Raspbian file is itself corrupted. If the Raspbian file got corrupted then sorry I can't help you. There may be a way to recover previously deleted files but I'm not that good with Linux.

Nonetheless there may be things you can do to get yourself back on the air:

1) All OS/8 media image files that the PiDP-8/I runs are in the Raspbian folder


On the assumption that you didn't change anything in your /opt/pdp8i/share/boot/0.script SIMH boot script file then the default OS/8 system disk media image is


If you did change the name of your OS/8 system disk media image, you might need to look into the text file /opt/pdp8i/share/boot/0.script to see what you changed it to.

At a minimum, make a backup copy somewhere of the OS/8 system disk media image so you can get back to it later. After copying it somewhere else, rename the file


to something like


2) With older versions of the PiDP-8/I SIMH software, there is a virgin copy of the .rk05 media files on a path something like one of these


If in one of those paths you can find the file v3d.rk05, then you can copy and paste it into


At that point, you should be able to boot OS/8 on that virgin OS/8 RK05.

If you can't find the file v3d.rk05 anywhere in the /home/pi/... tree then all is still not lost. You should be able to find the file


Just make a copy of this file and rename it as


then you should be at least bootable on a virgin RK05 system disk.

3) When you are back up and running OS/8 on a working RK05 system disk, you can now ctrl/e into SIMH and

sim> attach rk1 /opt/pidp8i/share/media/os8/OLDv3d.rk05
sim> go

When you are back in OS/8, try to take a directory of RKA1: and RKB1:. If you get a directory then the Raspbian file is probably OK and it's a matter of the media image having some bad blocks. If so, then you can OS/8 copy your files from the old RK05 in RKA1:/RKB1: onto the new one in RKA0:/RKB0:.

If you get any kind of OS/8 error when you try to get a directory of RKA1: and RKB1: then I would need to see what kind of error it is before knowing how to proceed. As long as the Raspbian file itself isn't corrupted, there are tools (FUTIL and Super TECO) that can be used to recover data off of corrupted OS/8 media.

Let me know how far you get and we can take it from there.

4) Now that you know that the media image files are in


In the future you should do something like this to back up your media image files:

a) in OS/8, ctrl/e to drop into SIMH. In SIMH,

simh> exit

This shuts down SIMH properly and closes the media image Raspbian files

b) make backup copies, like on a USB thumb drive, of the critical files in /opt/pidp8i/share/media/os8/. Then, if you crash again later, you can just recover your most recent backup image from the USB thumb drive.

"The error arose after running a machine code program that got stuck in a loop and I used the console switches ro reboot the RPi.  Should I have done a tidy shutdown from simh?  And if so how to I do a tidy shutdown and reboot from simh?"

I'm surprised because the console switches should have given you a tidy RPI shutdown. On the other hand, if you get into a runaway PDP-8 program in the future, there are several other options:

a) Hit the Stop switch on the front panel. Set the Switch Register switches to 007600 (000 000 111 110 000 000). Hit the Load Address switch. Hit Start. This is the softest reboot in OS/8 itself.

b) I don't recall the RK05 boot instructions, but it's very short. It's less than 4 words, I'm sure. You could re-toggle those into the front panel and hit Start. That would be a hard reboot of OS/8 but wouldn't affect SIMH.

c) From the running PiDP-8/i, hit ctrl/e to drop into SIMH. At the SIMH sim> prompt type exit. This drops you back into Raspbian OS. Type pidp8i start followed by pidp8i at the Raspbian prompts. This is a hard reboot of SIMH which also gives you a hard reboot of OS/8

"what does "set df disable" do in simh?"

It is either one of two different things. One is that it disables simulation of the DF32 disk drive. The other is that it configures the PiDP-8/I SIMH implementation to ignore the Data Field switches (the 3 front panel switches on the far left) so that you can use them to mount USB media sticks. It is one or the other of those two, I just don't remember which one.

Good luck,

-- steve

On Fri, Sep 23, 2022 at 10:57 AM Andrew Herbert <> wrote:

I have been exploring OS/8 on my PiDP8i for about a week now and made a lot of progress.

However, now when I attempt to start pidp8i the system hangs with the message:

PiDP-8/I pi4-gpio-clean:id[41daa2863b] [pi4b] [ils] [stdpcb] [gpio] [rt]
PDP-8 simulator V4.0-0 Current        git commit id: ab48f313

I can't get back to simh with ^E.

If I input ^C I get "Loading OS/8 from the RK05 cartridge disk..."

So I'm guessing something is corrupted on the disk?

Two questions:

1) Is there a way to repair the disc so I can keep all the files I've created, or
2) If I have to revert to a virgin disk, what do I copy from where to where?

The error arose after running a machine code program that got stuck in a loop and I used the console switches ro reboot the RPi.  Should I have done a tidy shutdown from simh?  And if so how to I do a tidy shutdown and reboot from simh?

Final and separate question, what does "set df disable" do in simh?  I couldn't find ti in the documentation...



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Ian Schofield

Sep 24, 2022, 10:46:03 AM9/24/22
to PiDP-8
Dear Andrew,

 This so easy to do!! You can sometimes get lucky. For this, it can be easier to use the basic pdp8 app from Simh rather than the PiDP8I app.
 First, find an RK05 OS/8 volume that works. There are several versions in the opt/pidp8i/share/media/os8 directory eg v3d-dist.rk05
 (Make a copy !!). In simh (pdp8) attach this file in RK0 and then attach your duff disk in RK1.
 boot rk0 and try DIR RKA1: (this is the sys: directory of you duff disk) and then DIR RKB1: (this is the DSK: directory of your duff disk).
 I assume your valuable programme is in DSK: so, if you can see a directory here, you can list your file and retrieve it.
Try this first and let us know how you get on.

Regards, Ian.

Ian Schofield

Sep 24, 2022, 10:47:31 AM9/24/22
to PiDP-8
Dear All,

 Ooops, just seen the above. Sorry Steve, duplicate suggestion!!!!

BW, Ian.

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