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Discrete 7400 logic based FPGA

A custom, modular FPGA architecture simulated in VHDL (GHDL), realized with discrete 7400-logic ICs, layouted on PCB with KiCAD and programmed through an abstraction layer via Arduino.

doc/img/fpga-arduino-1.jpg

Read the full thorugh process and many explanations on my blog: mnemocron.github.io

Motivation

Why build arguably the worst FPGA ever?

Ever since building Ben Eaters 8 bit CPU myself, I wanted to build something even crazier. The 8 bit CPU is arguably the worst CPU ever built - but it is a fantastic educational example. And that is the case for the 4 bit FPGA. It is a purely educational side project that boosted my knowledge about FPGA architecture, VHDL design and verification. Without further ado, here it is.

doc/img/architecture-tile.png

Build Process

The actual part list is WIP. Expected material cost are approximately 50 USD per assembled tile (4:4 bit LUT with interconnect).

doc/img/concept-to-pcb.png

Start Here!

Do you want to build this FPGA yourself? Great! Everything, I made regarding this project is in this repository.

To understand the architecture start with ./architecture or read about it on my blog. Next, you may dive into the VHDL simulations in ./vhdl and try out a few things. Head straight to the ./vhdl/test directory to see examples with the full FPGA architecture (instead of sub units).

  • ./architecture contains conceptual draw.io block diagrams
  • ./doc contains images, notes and tools that may be helpful
  • ./ihdl (WIP) contains ideas and concepts for a "compiler"
  • ./kicad contains schematics and PCB files for KiCAD 7.0
  • ./sketch contains Arduino code for testing of assembled PCB hardware and abstraction layer in C
  • ./vhdl contains models for 74xx ICs and the full FPGA architecture for simulation

"Assemble" code to map onto the FPGA in Arduino

doc/img/compiler-design.png

Inspiration & Honorable Mentions

Build an 8-bit computer from scratch

I built a programmable 8-bit computer from scratch on breadboards using only simple logic gates. I documented the whole project in a series of YouTube videos and on this web site. Watch this video for an introduction:

on eater.net

Build your own FPGA

Building a microcontroller or CPU out of discrete logic is a popular hobbyist pursuit, and it serves a useful purpose: building a CPU from scratch teaches you a lot about CPU architecture and tradeoffs; it's an interesting and instructive exercise. So, I wondered, wouldn't building an FPGA out of discrete logic be similarly educational?

on Nick's Blog

on Hackaday

Princeton Regonfigurable Gate Array

Build your own FPGA Chip or embedded FPGA IP with Python, and enjoy a fully open-source, auto-generated CAD flow specifically for your custom FPGA.

on github

on princeton.edu