ICemu - Emulate Integrated Circuits

icemu is a Python library that emulates integrated circuits at the logic level. For example, if you want to simulate a circuit with a decoder driving the clock pin of two shift registers, it would look like this:

dec = SN74HC138()
sr1 = CD74AC164()
sr2 = CD74AC164()
mcu_pin = OutputPin('PB4')

sr1.pin_CP.wire_to(dec.pin_Y0)
sr2.pin_CP.wire_to(dec.pin_Y1)
sr1.pin_DS1.wire_to(mcu_pin)
sr2.pin_DS1.wire_to(mcu_pin)

print(dec.asciiart())
     _______
   A>|-   +|>Y7
   B>|-   +|>Y6
   C>|-   +|>Y5
 G2A>|-   +|>Y4
 G2B>|-   +|>Y3
  G1>|+   +|>Y2
  Y0<|-___+|>Y1

You could then play with pins at your heart contents and have them "propagate" through wires and IC logic automatically.

See it in action

Here's a little video of the simulated seg7 example (see examples folder):

and here is the video of the exact same code running in real life!

What is it for

The goal of this library is to facilitate the testing and debugging of embedded software. When we run software on an embedded prototype, it's often hard to debug failures because we don't even know if the problem comes from hardware (wiring, it's always the wiring!) or software. Moreover, testing directly on a prototype often involves significant setup time.

With emulation, we have a quick setup time, introspection capabilities, all this stuff. We can then confirm the soundness of our logic before sending it to our prototype.

Killer feature: direct integration with your code

If you have a circuit with a microcontroller in it, you can simulate the circuit by directly plugging the code you're putting on the MCU in it. See examples.

Comparison with Verilog/VHDL

Being new to the world of electronics, I don't know much about full blown simulation solutions. However, from what I read about Verilog and VHDL, these tools seem to be about helping to design circuits.

ICemu's goal is not that! Its goal is to help you debug the software you're going to flash on your MCU. Python being easily hooked to C, you can, with a little abstraction layer, directly run your code on the simulator and debug it there.

What I've read about simulations on Verilog/VHDL simulators is that you supply it with a series of inputs you want to send to your circuits. That's insufficient! What I want to do is run my whole, complex software and have it supply the inputs and react to the outputs of my simulated circuit.

There's a possibility that my newbie-ness made me create a tool that already exists, however, and if that happened, please tell me so I can stop working on useless tools.

Why Python

Because it's used for debugging purposes, speed is not essential. Also, Python is easy to glue with C.

I've tried writing quick icemu prototype in C and Rust, but they were needlessly complicated. With Python, it's easy to write the software and add new chips. Because there's gonna be a lot of these chips to add, we might as well make this process as fast as possible.

How to use

You can install icemu with pip on python 3.4+:

$ pip install --user icemu

Then, you need to recreate your prototype's logic in a small Python program that uses icemu and wrap that into easy to use functions. Those functions should be designed to receive pin state change from the MCU and apply the logic change into your circuit. Make that program print relevant information so that you can assert your logic's soundness.

Then, write yourself a small Hardware Abstraction Layer at the pin/register level, embed your Python program like a regular C application would do, make your ifdefed functions call helper functions you've written in your Python program, compile and run!

Examples

There are examples in the examples folder. Follow instructions in the README file of each example.

License

LGPLv3, Copyright 2017 Virgil Dupras