PiDP-8/I Software

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What It Is

This repository is the current official PiDP-8/I software development nexus. Here we continue development of the software from the last stable version published on the project site. This software differs in several major ways from that prior stable release.

The release versions available from this site are "stable" in the sense that they represent a coherent new version of the software and they are no longer changing in major ways, as they did in the first months of development.

Getting Started: Source Code

The efficient method to get started is to install this software into an existing Raspbian installation on the Pi which you are using with the PiDP-8/I board.

You can download the latest release — cut on 2017.04.04 — as a Zip archive or a tarball. (About 5 MB each.)

See the README.md file for more information on how to install this into your OS.

Getting Started: Binary OS Images

Those with plenty of Internet bandwidth and a micro SD card they don't mind overwriting may prefer to download the software hosted here in binary OS image form. There are two versions, each based on Raspbian Jessie Lite and each roughly 400 MB:

  1. Multi-core version — This OS image is built with the incandescent lamp simulator which only works properly on the multi-core Raspberry Pi 2 and 3 boards. (All models.)

    It takes about one and a half of the four available CPU cores on a Pi 2 or Pi 3 while running about 20× faster than a real PDP-8/I.

  2. Single-core version — For those running on Raspberry Pi Model A+ and B+ boards or the Pi Zero, this alternative download disables the ILS feature. It also slows the simulator down so it uses only about half the available CPU power to leave some host CPU power for background tasks. This allows it to run PDP-8 software roughly 3-4× as fast as a real PDP-8/I, depending on the speed of the Pi you run it on.

    This image will also run on a multi-core Pi. It will run PDP-8 software slower than the ILS version, since it will also be affected by the intentional 50% CPU usage limit, but because each one of those cores are faster than a single-core Pi and the other cores can take the load of background tasks, it still manages to run PDP-8 software roughly 10× faster than a real PDP-8/I.

See the installation instructions for more information.

The binary OS releases are not always updated when the source code releases are cut, since it is a fair amount of work to do those binary releases. Addressing that is the topic of the next section.

Updating the Binary OS Release

As shipped, the binary OS images above also contain the PiDP-8/I software source code and Fossil, the tool that lets you download updated source code as it becomes available. Updating the software is therefore much simpler than downloading the whole OS all over again and overwriting your perfectly good SD card:

$ cd ~/pidp8i
$ fossil update
$ make && sudo make install
$ sudo systemctl restart pidp8i
$ pidp8i

That should put you back into the PiDP-8/I simulator with the new code running.

I say "should" because the above process isn't foolproof. There are many situations where you'll need to dig deeper into the process:

All of those situations and more are covered in the README.md file.

Learning More

Official Project Site

Much of the information on Oscar Vermeulen's PiDP-8/I project site still applies to this distribution of the software for the PiDP-8/I.

The main differences largely boil down to file name changes. For example, in Oscar's article "How to use the PiDP-8/I," the only difference I see in a quick skim is that you now have to type pdp8i at the Raspbian command line to attach your terminal to the PiDP-8/I simulator rather than pdp.sh.

Project Documentation

This software project has its own documentation and tutorials, which I've collected here for convenience:

SIMH Documentation

The PiDP-8/I software project is based on the actively-developed version of SIMH. (As opposed to the old frozen SIMH 3.9 version which still comes up high in search results.) That project has its own documentation, but for convenience I've provided PDF versions of the relevant subset here:

Rare PDP-8 Documentation

While most of the information about the PDP-8 is widely available on the Internet and may thus be easily found by Googling, we have a small number of documents here that are not so easy to come by, plus some links that don't seem to come up as high in Google searches as they ought to: