PDP-11-related things: PiDP11, PDP2011, etc.
The PDP2011 is a VHDL implementation of the PDP-11 CPU and various peripherals for it, written by Sytse van Slooten. Learn all about it here: https://pdp2011.sytse.net
I am running it on a CYC1000 FPGA development board: https://shop.trenz-electronic.de/en/TEI0003-03-QFCR4A-CYC1000-with-Intel-Cyclone-10-LP-10CL025-C8-8-MByte-SDRAM-8-MByte-Flash This a very reasonably-priced and easy-to-use FPGA board.
By default PDP2011 emulates a DEC RP06 disk drive, with a capacity of 176MB, on a SD card. Sytse provides a disk image of 2.11 BSD Unix. It runs well, but it really could use a bigger disk drive. (You can hardly buy a SD card smaller than 8GB these days...)
PDP2011 also supports the DEC RP07 drive, which holds 516MB. So I made a 2.11 BSD disk image for that drive, which you can download from here. It is quite up-to-date, at patchlevel 489 for 3/31/2025.
Here is how you can use it:
1: Get PDP2011 running, on a CYC1000 board or some other suitable FPGA board. The author provides excellent documentation at https://pdp2011.sytse.net
2: Ensure that the RP06 drive actually works on your system, using Sytse's 2.11 BSD image or one of the other operating system images he has provided.
3: You will need to rebuild PDP2011, so download and install the (free) Quartus Lite FPGA development system from https://www.intel.com/content/www/us/en/products/details/fpga/development-tools/quartus-prime/resource.html
4: Do the one-line change to the PDP2011 VHDL code to enable the RP07 instead of the RP06 drive, and rebuild the system in Quartus. This is not nearly as scary as it sounds.
5: Copy my new disk image to a SD card (the same way you did it in step 2 above), and boot it up!
6: I highly recommend getting Ethernet networking running on the PDP2011 - it makes 2.11 BSD Unix much easier to use. I used this Ethernet interface board, which PDP2011 supports out-of-the-box: https://www.olimex.com/Products/Modules/Ethernet/MOD-ENC624J600/. I 3d-printed a little box to hold the board - it fits within the PiDP-11 case.
If you ever feel like building a new Unix image from a 2.11 BSD distribution tape, you can use my file PDP2011.config as a starting point. I based my build on the distribution tape image at https://www.tuhs.org/Archive/Distributions/UCB/2.11BSD-patch481/. I followed Sytse's excellent instructions at https://pdp2011.sytse.net/wordpress/howto/2-11bsd-rp06/, and the entire process was much less difficult than I expected. Of course you have to replace all usages of 'rp06' with 'rp07', and use the correct rp07-specific boot program. You also have to decide what your disk partition arrangement will be. The partitions here were suggested by Sytse - you can find a description of them in the file disklabel.txt.
The CYC1000 FPGA board is connected to the PiDP-11 circuit board with one of Sytse's little adapter "shim" boards, as described here: https://pdp2011.sytse.net/wordpress/pdp-11/fpga-boards/cyc1000/. I ordered 10 of them (the minimum order) from Seeed in China, so let me know if you need one.
I also used:
- A micro USB panel-mount cable and an Ethernet panel-mount cable, both from Adafruit. Note how I had to carefully carve away some of the plastic on the panel-mount connectors so they would fit inside the case.
- The Olimex Ethernet board mentioned above. I 3d-printed a little box to hold the board (OpenSCAD and STL files above). It fits within the PiDP-11 case if you clip off the unneeded header pins on the bottomof the Ethernet board. The box is mounted to the PiDP-11 circuit board with double-sided sticky foam tape.
- A Digilent PMOD to micro-USB board. This board is very simple - all passive components.
- A Digilent dual PMOD cable. I had to modify the plug that connects to the Ethernet board: that board did not have the standard PMOD pinout, so I had to remove the cable's female pins from the original 1x6 connector and install them into a 2x5 connector that fits the Ethernet board. (Take care to be sure that each signal goes to the correct place!)
- A generic SD card extender. This got mounted on the back of the PiDP-11 case for easy access. The extender I used had sockets for both regular and micro SD cards, so I could use some old full-size SD card I had lying around. The connection from the extender to the PMOD SD socket was secured and protected with a good wrap of electrical tape. :-)
Here is a close-up of the Ethernet board and its conenctions and mounting. The 52 header pins that stuck out of the bottom were totally unneeded for this application, and had to be clipped off to allow it to fit in the PiDP-11 case. (Unsoldering the pins woud have been more elegant, but a major pain to do...)
Here is a view of everything installed and closed up. (Those huge ugly screws were supplied with the PiDP-11 kit...)
