Unix on a Pi Pico

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Mar 26, 2022, 2:41:42 PM3/26/22
to [PiDP-11]
Dear All,

 Here is some more software for entertainment purposes.
 There has be quite a few articles on the web about running Unix on various devices.
 One in particular caught me eye namely Fuzix: How to get started with FUZIX on Raspberry Pi Pico - Raspberry Pi
 It then occurred to me that it might be possible to run a 'proper' version of Unix on a Pi Pico
 As you can imagine, getting a full Simh app to run might be quite difficult.
 A quick search of the web revealed a PDP11 VM with a very small footprint that might suit the requirement. I found an excellent app created by Dave Cheney: davecheney/avr11: PDP11/40 simulator for atmega2560 (github.com)
After some relatively minor changes, the code for this is attached which is sufficient to run a cut down version of Unix which is comparable to V5.
The disk images may be found at: Mini-UNIX (tavi.co.uk). For this project you will need mxrk05a.img on an SD card attached to the Pico (see rk05.cpp).
The hardware I am using is the Pico DV card from Pimeroni: Pimoroni Pico DV Demo Base - Pimoroni
The app uses the Pimeroni library that creates an SDcard interface via the Pico's PIO system. This is really cool in itself in that the built-in SPI interface is not required and the PIO interface can be attached to most of the Pico pins if you wish to change them.
See Pico_PDP11/Pico_RT11/Cmake.lists.
As you will note, this is a cmake project for which I use Visual Studio Code as the devenv. I hope no one minds if I say that this is not the easiest system to use! Also, the launch.json file is setup to use OpenOCD as a programmer via another Pico running Picoprobe. And, the terminal is attached via USB. This will need a bit of homework to setup as well such that I think I spent as much time configuring VSCode as I did writing the app!.
Finally, a PDP11 Unix (rkmx at the @ prompt) was running on the Pico and it is not bad at all. See the manuals at the Tavi site for more details.
You might be asking yourself what is the purpose of this exercise. Primarily, it is to publicise Dave Cheney's work in creating a very simple PDP11 VM which is in the same vein as the Nano8 system on the PiDP8I group. This lies between Sytse's FPGA implementation and the complexity of Simh. Also, it would be quite possible to extend the app to simulate an 11/70 and use the PIO system to drive Oscar's beautiful front panel as Dave Betz is doing for the PiDP8I. 
In addition, I would ask to you to have a look
at: https://www.jcwolfram.de/projekte/main.ph as well for an implementation on the STM series as well.
NBNB Rt11V4 RK05 image in the zip as well.



Mar 27, 2022, 12:59:11 PM3/27/22
to [PiDP-11]
Wow a PDP11 on a chip that costs $5 :-) Amazing.

I have a tiny SD reader board with MOSI/MISO , so hopefully I can just wire that directly to the Pico.

Then.. copy the disk image to the SD card and then copy the binary created by the Visual Studio build directly to the Pico?


Mar 30, 2022, 5:31:46 PM3/30/22
to [PiDP-11]
Dear John,

 Should work. Use the SD connections as per the schematic of the Pimeroni board:  pico_dv.sch (shopify.com)
Good luck!
BW, Ian.


Dec 14, 2022, 1:01:52 PM12/14/22
to [PiDP-11]
Dear All,

 Some minor updates in relations to the above and some most welcome help from Guido Lehwalder.
 and is a bit more stable. RL01/02 handler in progress and a very minimal Simh like interface.
 A bit more work required before this device can drive Oscar's PiDP11 panel.

BW, Ian.
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