Haskell to VHDL/Verilog/SystemVerilog compiler
Clash - A functional hardware description language
Clash is a functional hardware description language that borrows both its syntax and semantics from the functional programming language Haskell. The Clash compiler transforms these high-level descriptions to low-level synthesizable VHDL, Verilog, or SystemVerilog.
Features of Clash:
Strongly typed, but with a very high degree of type inference, enabling both safe and fast prototyping using concise descriptions.
Interactive REPL: load your designs in an interpreter and easily test all your component without needing to setup a test bench.
Higher-order functions, with type inference, result in designs that are fully parametric by default.
Synchronous sequential circuit design based on streams of values, called
Signals, lead to natural descriptions of feedback loops.Support for multiple clock domains, with type safe clock domain crossing.
Open-source community
Clash benefits from an active community. Whether you need a question answered or want to contribute to open-source features, browse the features below to make the most of Clash.
- Discourse: long form discussions and questions
- Discord: short form discussions and community chat room
- Fosstodon: microblogging and community chat room
- Bluesky: microblogging and community chat room
- Github: issue tracker
Get Clash
Check out clash-lang.org/install to install the latest stable release of Clash, or to setup a Clash project.
Get Clash from source
Get the source code using Git and enter the cloned directory:
git clone git@github.com:clash-lang/clash-compiler.git
# Alternatively, if you haven't setup SSH keys with GitHub:
# git clone https://github.com/clash-lang/clash-compiler.git
cd clash-compiler
To check out a released version, use:
git checkout v1.2.3
To checkout a release branch use:
git checkout 1.2
Note that release branches might contain non-released patches.
GHC compatibility
| Linux | Windows | macOS | Clash (released) | Clash (development version) | |
|---|---|---|---|---|---|
| 8.6 | ✔️ | ✔️ | ✔️ | 1.0 - 1.8 | ❌ |
| 8.8 | ✔️ | ❌ | ✔️ | 1.0 - 1.8 | ❌ |
| 8.10 | ✔️ | ✔️ | ❌ | 1.2 - 1.8 | ❌ |
| 9.0 | ✔️ | ✔️2 | ✔️ | 1.4 - 1.8 | ❌ |
| 9.2 | ⚠️1 | ⚠️1 | ⚠️1 | 1.8 | ❌ |
| 9.4 | ⚠️3 ️ | ⚠️3 | ️⚠️3 ️ | 1.8 | ❌ |
| 9.6 | ✔️3 | ✔️3,4 | ✔️3 | 1.8 - 1.10 | ✔️ |
| 9.8 | ✔️ | ✔️4 | ✔️ | 1.8 - 1.10 | ️✔️ |
| 9.10 | ✔️ | ✔️4 | ✔️ | 1.8 - 1.10 | ️✔️ |
| 9.12 | ✔️ | ✔️4 | ✔️ | 1.10 | ️✔️ |
1 GHC 9.2 contains a regression, rendering Clash error messages indecipherable. This change was reverted in 9.4.
2 GHC 9.0.2 on Windows fails to compile clash-cores. We therefore don't run the Clash test suite on CI for this combination.
3 Clash starts extremely slowly when compiled with 9.4.8 up to and including 9.6.2. Consider downgrading to 9.4.7 or upgrading to 9.6.3 and up.
4 Clash starts extremely slowly on Windows with GHC 9.6 through 9.12, consider downgrading to 9.4.7
Cabal
To use Cabal you need both Cabal and GHC installed on your system. We recommend using ghcup. For more information, see https://www.haskell.org/downloads/.
To run clash use:
cabal v2-run -- clash
If this fails, make sure you've got an up-to-date package index:
cabal update
Stack
Install Stack and run:
stack run -- clash
Nix
Or use Nix to get a shell with the clash and clashi binaries on your PATH:
# Start the default dev shell
nix develop .
# Start a dev shell with a specific GHC version
nix develop .#ghc9103
You will need a modern version of nix with support for the new-style nix
command and flakes (2.4 or newer). Support for these must still be manually
enabled, this can be done by setting
experimental-features = nix-command flakes
in your nix.conf.
The flake is configured to use the clash-lang Cachix binary cache.
When you first run nix develop, Nix will ask whether to allow and trust the
cache. Accepting avoids having to build Clash from source.
To automatically enter and exit the nix environment on directory change, you
can install direnv and
nix-direnv and write the
following to a .envrc file in the root of this repository:
use flake
watch_file nix/*
Upon adding or changing this file you must direnv allow in order for the file
to be automatically loaded / reloaded on project changes.
Individual packages / applications can also be built or run using the nix build and nix run commands, i.e.
nix build .#clash-ghc
nix run .#clashi
Hacking
Want to start hacking on Clash? Read HACKING.md for tips and tricks.
Related libraries and initiatives
- Clashilator: tooling to integrate Clash with Verilator. Enables fast, multithreaded simulation by compiling Clash designs to C++.
- Clash Protocols: experimental library for writing Clash circuits with bidirectional communication - such as AXI or Avalon.
- Clash Starters: starter projects to quickly get you up and running.
- Clash WaveDrom: generate wave diagrams from Clash using WaveDrom
Projects built with Clash
- Contranomy: a RISCV implementation verified using the RISC-V Formal Verification Framework.
- Space Invaders: a Clash implementation of the 1978 Space Invaders arcade machine by Taito.