README.md

74aoc

A PCB solving Advent of Code 2025 Day 1 using 125 discrete 74-series logic chips synthesized via an automated Hardcaml -> nextpnr -> KiCad pipeline.

Full writeup can be found on my blog.

Quick orientation guide:

• pcb/ contains the KiCad files. For reproducibility, those are "cooked" files that include the solution design loaded and routed (revert the appropriate commits for a fresh blank slate)
• hdl/ contains the Hardcaml source code and the Yosys+nextpnr orchestration. Some of the intermediate files are also commited for traceability.
  • dune exec ./test_solution.exe runs the Hardcaml test bench
  • dune exec ./build_solution.exe outputs the Verilog source code from the Hardcaml solution (beware that this requires the preview version 0.18 of Hardcaml)
  • top.v includes the output of the previous step and wraps it to assign concrete IO pads to the signals
  • ./simulate.sh <preplace|pnr> runs the Verilog testbench using Verilator, either on pre-placement Verilog or on the placement result from Nextpnr (using the appropriate cell models from nextpnr-generic)
• The root directory contains several scripts that serve to translate results from hdl into pcb. Loading new design is done by running translate_nets_to_kicad.py and load_luts_into_kicad.py.
• controller/ this contains the bit banged driver for the board, to be executed on Raspberry Pi. Executed as dune exec ./main.exe, supports --help.