Tydi-Clash
Simple Starter Project
This starter project contains the scaffolding needed to integrate Clash with the Cabal and Stack build systems. It allows you to use dependencies from Hackage easily.
Table of Contents
Getting this project
Stack users can run stack new my-clash-project clash-lang/simple. Cabal users can download a zip containing the project.
Building and testing this project
There's a number of ways to build this project on your machine. The recommended way of doing so is using Stack, whose instructions will follow directly after this section.
Stack (Windows, Linux, MacOS) [recommended]
Install Stack using your package manager or refer to the How to install section of the Stack manual.
Build the project with:
To run the tests defined in tests/, use:
To compile the project to VHDL, run:
You can find the HDL files in vhdl/. The source can be found in src/Example/Project.hs.
Cabal (Linux, MacOS)
The following instructions only work for Cabal >=3.0 and GHC >=8.4.
First, update your cabal package database:
You only have to run the update command once. After that, you can keep rebuilding your project by running the build command:
To run the tests defined in tests/, use:
To compile the project to VHDL, run:
You can find the HDL files in vhdl/. The source can be found in src/Example/Project.hs.
REPL
Clash offers a REPL as a quick way to try things, similar to Python's python or Ruby's irb. Stack users can open the REPL by invoking:
Cabal users use:
IDE support
We currently recommend Visual Studio Code in combination with the Haskell plugin. All you need to do is open this folder in VSCode; it will prompt you to install the plugin.
Project overview
This section will give a tour of all the files present in this starter project. It's also a general introduction into Clash dependency management. It's not an introduction to Clash itself though. If you're looking for an introduction to Clash, read "Clash.Tutorial" on Hackage.
tydi-clash
├── bin
│ ├── Clash.hs
│ └── Clashi.hs
├── src
│ └── Example
│ └── Project.hs
├─── tests
│ ├── Tests
│ │ └── Example
│ │ └── Project.hs
│ ├── doctests.hs
│ └── unittests.hs
├── cabal.project
├── tydi-clash.cabal
└── stack.yaml
tydi-clash.cabal
This is the most important file in your project. It describes how to build your project. Even though it ends in .cabal, Stack will use this file too. It starts of with meta-information:
cabal-version: 2.4
name: tydi-clash
version: 0.1
license: BSD-2-Clause
author: John Smith <john@example.com>
maintainer: John Smith <john@example.com>
If you decide to publish your code on Hackage, this will show up on your package's front page. Take note of the license, it's set to BSD-2-Clause by default, but this might bee too liberal for your project. You can use any of the licenses on spdx.org/licenses. If none of those suit, remove the license line, add license-file: LICENSE, and add a LICENSE file of your choice to the root of this project. Moving on:
common common-options
default-extensions:
BangPatterns
BinaryLiterals
ConstraintKinds
[..]
QuasiQuotes
-- Prelude isn't imported by default as Clash offers Clash.Prelude
NoImplicitPrelude
Clash's parent language is Haskell and its de-facto compiler, GHC, does a lot of heavy lifting before Clash gets to see anything. Because using Clash's Prelude requires a lot of extensions to be enabled to be used, we enable them here for all files in the project. Alternatively, you could add them where needed using {-## LANGUAGE SomeExtension #-} at the top of a .hs file instead. The next section, ghc-options, sets warning flags (-Wall -Wcompat) and flags that make GHC generate code Clash can handle.
Note that this whole section is a common "stanza". We'll use it as a template for any other definitions (more on those later). The last thing we add to the common section is some build dependencies:
build-depends:
base,
Cabal,
-- clash-prelude will set suitable version bounds for the plugins
clash-prelude >= 1.8.2 && < 1.10,
ghc-typelits-natnormalise,
ghc-typelits-extra,
ghc-typelits-knownnat
These dependencies are fetched from Hackage, Haskell's store for packages. Next up is a library stanza. It defines where the source is located, in our case src/, and what modules can be found there. In our case that's just a single module, Example.Project.
library
import: common-options
hs-source-dirs: src
exposed-modules:
Example.Project
default-language: Haskell2010
Note that extra dependencies could be added by adding a build-depends line to this section. The following section defines a testsuite called doctests. Doctests are tests that are defined in the documentation of your project. We'll see this in action in src/.
test-suite doctests
type: exitcode-stdio-1.0
default-language: Haskell2010
main-is: doctests.hs
ghc-options: -Wall -Wcompat -threaded
hs-source-dirs: tests
build-depends:
base,
tydi-clash,
doctest-parallel >= 0.2 && < 0.4,
Last but not least, another testsuite stanza is defined:
test-suite test-library
import: common-options
default-language: Haskell2010
hs-source-dirs: tests
type: exitcode-stdio-1.0
ghc-options: -threaded
main-is: unittests.hs
other-modules:
Tests.Example.Project
build-depends:
tydi-clash,
QuickCheck,
hedgehog,
tasty >= 1.2 && < 1.6,
tasty-hedgehog,
tasty-th
These testsuites are executed when using stack test or cabal test. Note that Cabal swallows the output if more than one testsuite is defined, as is the case here. You might want to consider running the testsuites separately. More on tests in /tests.
cabal.project
A cabal.project file is used to configure details of the build, more info can be found in the Cabal user documentation. We use it to make Cabal always generate GHC environment files, which is a feature Clash needs when using Cabal.
cabal.project can be used to build multi-package projects, by extending packages.
stack.yaml
While Cabal fetches packages straight from Hackage (with a bias towards the latest versions), Stack works through snapshots. Snapshots are an index of packages from Hackage know to work well with each other. In addition to that, they specify a GHC version. These snapshots are curated by the community and FP Complete and can be found on stackage.org.
This project uses lts-19.32, which
includes Clash 1.6.4. Snapshots tightly couple GHC and package versions. By
working this way, Stack projects build on a cohesive set of packages. Plus, it
guarantees that if a stack build works now, it will work in 10 years too.
Note: If you need a newer Clash version, simply change the version bounds in tydi-clash.cabal and follow the hints given by Stack.
src/
This is where the source code of the project lives, as specified in tydi-clash.cabal. It contains a single file, Example/Project.hs which starts with:
module Example.Project (topEntity, plus) where
import Clash.Prelude
-- | Add two numbers. Example:
--
-- >>> plus 3 5
-- 8
plus :: Signed 8 -> Signed 8 -> Signed 8
plus a b = a + b
tydi-clash.cabal enabled NoImplicitPrelude which enables the use of Clash.Prelude here. Next, a function plus is defined. It simply adds two numbers. Note that the example (>>> plus 3 5) gets executed by the doctests defined for this project and checked for consistency with the result in the documentation (8).
-- | 'topEntity' is Clash's equivalent of 'main' in other programming
-- languages. Clash will look for it when compiling 'Example.Project'
-- and translate it to HDL. While polymorphism can be used freely in
-- Clash projects, a 'topEntity' must be monomorphic and must use non-
-- recursive types. Or, to put it hand-wavily, a 'topEntity' must be
-- translatable to a static number of wires.
topEntity :: Signed 8 -> Signed 8 -> Signed 8
topEntity = plus
as the comment says topEntity will get compiled by Clash if we ask it to compile this module:
or
We could instead ask it to synthesize plus instead:
If you want to play around with Clash, this is probably where you would put all the definitions mentioned in "Clash.Tutorial" on Hackage.
tests/
Most of this directory is scaffolding, with the meat of the tests being defined in tests/Tests/Example/Project.hs. Writing good test cases is pretty hard: edge cases are easy to forget both in the implementation and tests. To this end, it's a good idea to use fuzz testing. In this project we use Hedgehog:
import Example.Project (plus)
prop_plusIsCommutative :: H.Property
prop_plusIsCommutative = H.property $ do
a <- H.forAll (Gen.integral (Range.linear minBound maxBound))
b <- H.forAll (Gen.integral (Range.linear minBound maxBound))
plus a b === plus b a
This test generates two numbers a and b that fit neatly into domain of Signed 8, thanks to the use of minBound and maxBound. It then tests whether the plus operation commutes. I.e., whether a + b ~ b + a. All functions called prop_* are collected automatically:
We can run the tests using stack test or cabal run test-library:
.
Tests.Example.Project
plusIsCommutative: OK
✓ plusIsCommutative passed 100 tests.
All 1 tests passed (0.00s)
Change the license
By default tydi-clash.cabal sets its license field to BSD-2-Clause. You might want to change this.