verilogpdp

Synthesizable Verilog implementations from original schematics of Digital Equipment Corporation PDP series of computers

Currently features a PDP-8/I implementation. Very much a work-in-progress.

Changelog:

• 20210322 KVO: Added TC08/TU55 support. Now boots OS/8!!
• 20210302 KVO: Added TTY input support. Currently configured as loopback for test purposes. Slowed baud rate clock to 230.4k. Added "ctrl-e" to print status of PDP-8 while running. Now runs FOCAL-69! Added support for counting machine cycles and support for halting after some number of machine cycles.
• 20210227 KVO: Passing CPU and EAE MAINDECs; see results in successful_run.txt. Cleaned up Makefile a bit.
• 20210226 KVO: Design speed is back to 100 MHz to lengthen minimum pulses and to make glitch detection easier for the SN7474 model. SN7474 captures data from two master clock cycles previous, and requires two consecutive asserted signals on the asynchronous clear and preset inputs to activate. Appears to pass MAINDECs 8I-D01C, 8I-D02B, 8I-D0AA, 8I-D0BA, 08-D04B, 08-D05B, and 08-D07B.
• 20210224 KVO: Removed power pins from M310. Changed default M452 baudrate to significantly higher value to speed up simulation. Fixed EAE_RUN signal in main netlist so that EAE now starts correctly. SN7474 now captures data from previous clock edge to fix edge case of data/clock changing simultaneously. Added command line parser to sim_main.cpp along with timing information. Now can start logging at a specific time to reduce log file size and increase simulation speed. Changed design clock speed from 100 MHz to 20 MHz to further increase simulation speed (not well tested yet).
• 20210222 KVO: Added TTY output support. Passes MAINDEC-8I-D01C and MAINDEC-8I-D02B! Also prints "hello world" after running both MAINDECs for a bit. Cleaned up test suite. Extended power-on reset pulse. Refactored test control code.

Requirements:

Verilator to simulate the model, and optionally GTKWave to view the results.

Usage:

To boot OS/8 with the TC08/TU55, just type make. After several minutes, a dot prompt will appear. It's interactive, but be forewarned: the simulation is typically around 1/1000 of original speed. To print the directory listing takes about an hour on my computer.

Other targets are available as well; read the Makefile to see what you can run. When running with logging, a log file will appear under logs. Logging can increase runtime and generate very large files, so beware!

Acknowledgements:

A big thank you to Vince Slyngstad, for his high-quality redrawn schematics, and patience through debugging the model. This project would not be possible without him and his tireless efforts. The schematic used for this model so far comes from http://svn.so-much-stuff.com/svn/trunk/Eagle/projects/DEC/PDP8I/

His site has many other wonderful nuggets of information, so please check it out: https://so-much-stuff.com/pdp8/index.php