ners/riscv-hs

A RISC-V emulator in Haskell

RISCV-HS

A logical model of a minimal RISC-V CPU written in Haskell.

This is an exercise to learn Nix, Haskell, and RISC-V. It is not intended to be useful, fast, or even complete.

The goal is to understand the inner workings of the RISC-V architecture from the bottom-up and learn Haskell concepts on the way. A possible outcome would be an emulator that can run RV32I assembly.

Requirements

• Install Nix
  • follow instructions on https://nixos.org/download
• Enable flakes
  • follow instructions on https://nixos.wiki/wiki/Flakes#Enable_flakes
• (Optional) install direnv

Project structure

• The structure of the project is dictated by the tools we are using, namely Nix and Cabal. This repository is both a Nix flake and a Cabal package and as such contains the following folders/files:
  • app/: Haskell source code for an executable that can be built and run by cabal run.
  • src/: Haskell library folder, each file inside is a Haskell module.
  • test/: Haskell source code for an executable that is built and run by cabal test, used to test the functions defined in src/.
  • CHANGELOG.md: This file will only become relevant in case of a release.
  • flake.nix: This is a Nix flake providing dependencies for the project.
  • flake.lock: File specifying the exact versions of dependencies, created by the nix flake lock command.
  • LICENSE: The Apache 2.0 license.
  • riscvs-hs.cabal: Cabal package description.
  • shell.nix: For compatibility with Nix without flakes as well as other tools.

Notes

• If you're using VSCode, you can use Nix environment selector to connect it with the Nix shell.

References

The RISC-V Instruction Set Manual

riscv-hs's Issues

Add boolean implication function

Implication is a binary function (e.g. a `implies` b)

• add the function to the Bits library
• test the function using property testing

Add project structure to readme

Please add a section in the readme that describes the project structure. This section should help people new to the project understand what each file and directory is for.

Implement half and full binary adder

Here are some resources that describe adders:

• https://www.geeksforgeeks.org/half-adder-in-digital-logic/
• https://www.geeksforgeeks.org/full-adder-in-digital-logic/

Let's put these into a new file, src/Adders.hs.

Do not test them in this PR, because that is tracked in a separate issue: #10

Test binary adders

Once #9 is merged, implement tests for the binary adders.

Let's put the tests to a separate file, test/Adders.hs, but call them from Main.hs.

Add property tests for other bitwise functions

We don't yet test every function. Try to cover the remaining ones.