sv2chisel (System)Verilog to Chisel Translator

Maintenance License GitHub tag (latest SemVer)

sv2chisel translates synthesizable (System)Verilog to low-level Chisel.

The resulting Chisel is intended to be manually refactored to benefit from the advanced Chisel's features such as type and functional parameterization thanks to Scala support for polymorphism and high-order functions. Several research efforts, such as this paper, demonstrate in practice the relevance of such refactoring.

sv2chisel has achieved 1:1 translation of several large codebases with few or no manual modifications. Discover all Features & Limitations

sv2chisel emerged as a research effort, if you use it or borrow some concepts in your own work, please cite the associated paper (bibtex entry below).

Project Contents

The current repository holds the sv2chisel project which is divided in two parts:

Getting Started

Get sv2chisel

Note: the version of sv2chisel x.5.x is aligned on Chisel stack 3.5.x and the versioning intends to follow the same evolution as Chisel stack one on minors

Native Binaries

sv2chisel releases provide native standalone binaries for the following platforms:

  • Linux (tested on a regular basis on Ubuntu 20.04)
  • Darwin (tested on a regular basis on MacOS with Darwin Kernel Version 17.7.0)
  • Windows (tested on windows 10 -- git-bash is recommended for colored console printing)

Just chmod u+x sv2chisel_<build> and you are all set for your first translation!


sv2chisel releases also provide a standalone jar file which only require a jvm installation.

Just untar -xzf sv2chisel_jar.tar.gz and you are all set for your first translation!

From code

Finally, sv2chisel code can be directly executed with any working sbt installation by cloning this repository, see direct usage from sources.

Setup your own Chisel project

If this is your first time using Chisel, we highly recommend you to follow either the online bootcamp or the chisel-tutorials first.

To set-up efficiently a new Chisel project, the easiest way is to clone the chisel-template.

As final step, you need to include sv2chisel-helpers library in this new project, by adding the following line to your local build.sbt file:

// sv2chisel was first published in 2021, on new sonatype servers hence requiring non default resolvers
resolvers ++= Seq(
  "New Sonatype Snapshots" at "",
  "New Sonatype Releases" at "",
// For simpler usage, sv2chisel minor version is aligned on chisel stack minor version: x.5.x 
libraryDependencies += "com.ovhcloud" %% "sv2chisel-helpers" % "0.5.0"

This new project is intended to be used as output target for the Chisel files converted from your (System)Verilog sources.


Complete 4-steps process, from (System)Verilog descriptions to upgraded Chisel generators:

  1. Translation
  2. Creation of a Chisel main
  3. Correctness Test
  4. Manual upgrade of the 1-1 translation to more idiomatic scala/chisel syntaxes

1. Translation

Option A: Create a config file for your HDL project


Then simply run sv2chisel with this config file:

./sv2chisel -c config.yml

Additional option (such as verbosity control) can be found with ./sv2chisel -help

Option B: Raw CLI Usage

See ./sv2chisel -help to get started, basic usage:

./sv2chisel <path/to/> ... <path/to/>


Please review and fix (or at least acknowledge) any error (fatal/critical) messages reported by sv2chisel before proceeding any further, as the generated Chisel code will probably not be usable in such cases.

Do not hesitate to raise an issue here in case of trouble.

2. Creation of a Chisel Main

In order to check the translation correctness of the translation, let's now translate it back to Verilog! Yeah it sounds silly but it's the way it works: Chisel is an hardware construction language, not intended to be provided directly to synthesis and simulation tools but rather to be executed and produce a low-level Verilog, almost down to netlist.

Getting started with Chisel generation API can be a bit frightening for Scala/Chisel newcomers, fortunately sv2chisel is able to generate that boilerplate for you. See details about specifying a top-level in the config file or Manual setup example below.

In a nutshell, just set the translationOptions.Chiselizer.topLevelChiselGenerators option in your config file, using the syntax presented in the example config file

It will generate an object App such as object my_moduleGen extends App {/* */}. To generate your Verilog, run this app with sbt runMain my_moduleGen if placed in src/main/scala or with sbt Test / runMain my_moduleGen if placed in src/test/scala.

Error reporting

  • compile step should not raise errors, if it does, please raise an issue here
  • Similarly, Chisel elaboration step (in between Elaborating... and Done elaborating. message) should not raise errors, if it does, please raise an issue here
  • Finally, FIRRTL compilation step might raise errors, in particular related to missing connections in your design. This is due to a strict Chisel/FIRRTL toolchain policy: no declared wire shall be left unassigned and no latches are allowed. If you do get such errors, you are welcome to fix them yourself either in the verilog or the generated chisel, but do not hesitate reach the very welcoming Chisel/FIRRTL community for help!

3. Test: Check translation correctness

You can now integrate the chisel-emitted Verilog into your usual simulation and synthesis flow, and check that it is consistent. Simulation should pass and synthesis produce on-par resource usage results. If it is not the case, investigate the translation result, be sure you understand the implication of every warning message and feel free to open an issue for help or to raise a discovered bug.

Beware that ports are flattened in the resulting verilog, you might hence need a verilog wrapper to integrate the resulting verilog, fortunately sv2chisel can bring it to you!

  • a port myport: Vec(n+1, <>) (verilog [N:0]) becomes n ports from myport_0: <> to myport_n: <>
  • a port myport: Bundle (verilog struct) becomes several individual ports named after the fields names such as myport_myfieldA ... myport_myfieldN

4. Upgrade your low-level Chisel

Your translated project is working as expected? Here is precisely where the whole fun starts, and where this step-by step guide stops. Please refer to Chisel documentation for various user-guides and examples to truly unleash Chisel's generation powers.

Citing this work

If you use this work or borrow some concept for your own research, please cite the following paper:

  author    = {Jean Bruant and
               Pierre-Henri Horrein and
               Olivier Muller and
               Tristan Grol{\'{e}}at and
               Fr{\'{e}}d{\'{e}}ric P{\'{e}}trot},
  title     = {(System)Verilog to Chisel Translation for Faster Hardware Design},
  booktitle = {Proceedings of the 31th International Workshop on Rapid System Prototyping,
               {RSP} 2020, Virtual Conference, September 24-25, 2020},
  publisher = {{ACM}},
  year      = {2020},


You've developed a new cool feature? Fixed an annoying bug? We'd be happy to hear from you!

Getting Started

If you have successfully published sv2chisel locally, then you are all set to start hacking into the code, otherwise see direct usage from sources.


The in-code documentation remains yet quite sparse. Here is a quick overview of the code base, within src/main/:

  1. Lexing & Parsing to IR
    • antlr4/ ANTLR SystemVerilog Lexer & Parser (generates Java sources within sv2chisel/target/scala-2.12/src_managed/main/antlr4/sv2chisel/antlr/)
    • scala/sv2chisel/Visitor.scala Visits the AST generated by the parser and map it into our custom Intermediate Representation (IR)
    • scala/sv2chisel/ir/ describe our IR which is based on Firrtl. Main content seats within IR.scala while the side files provide many convenient implicit functions operating on the IR.
  2. Transforms
    • scala/sv2chisel/Driver.scala contains the list of transforms applied to a project
    • scala/sv2chisel/transforms/ folder contains all the transforms
  3. IR to Chisel
    • scala/sv2chisel/Chiselizer.scala provide implicit functions to convert the IR into Chisel tokens. Note that some constructs of the IR are expected to be removed prior this step, thanks to previous transforms.
    • scala/sv2chisel/Emitter.scala synchronize the chisel token stream with the original token stream in order to re-insert comments and some part of the layout into the final Chisel text to be written to file.


All unit-tests can be found within src/test and can be run with sbt test for the whole batch or with testOnly sv2chiselTests.TestName for a particular one. Please add new test-cases along with new features or bug fix to highlight the quality of your contribution.

During main development process, functional testing was carried out both with the open-source RISC-V core PicoRV32 and some internal verilog libraries at OVHcloud.

Continuous integration system including such automated functional testing is under investigation.

Sharing your modifications

Have a look in and feel free to submit a pull-request on this repository.

Release to Maven Central


  • NB: Based on sbt-pgp & sbt-sonatype plug-ins
  • Add Credentials in ~/.sbt/1.0/sonatype.sbt
credentials += Credentials("Sonatype Nexus Repository Manager",
        "", // created after 2021
  • Add PGP private key in your/CI keyring

Release options

sbt:sv2chisel> publishSigned
sbt:sv2chisel> helpers/publishSigned
  1. RELEASE: Based on sbt-release plugin, just follow the instruction of sbt 'release'

Related links


External licenses

sv2chisel license



Direct Usage From Sources


Publish locally sv2chisel & sv2chisel-helpers

git clone
cd sv2chisel

In sbt shell

sbt:sv2chisel> publishLocal
sbt:sv2chisel> helpers/publishLocal

The publishLocal commands make sv2chisel and sv2chisel-helpers libraries available locally to be used in other Scala project.


Option A: Run the generic application

Either from shell

sbt 'runMain sv2chisel.Main -c config.yml'

or directly in sbt to avoid sbt startup time

sbt:sv2chisel> runMain sv2chisel.Main -c config.yml

Running runMain sv2chisel.Main -help details available options, in particular control of the level of verbosity.

Option B: Create your own translator app


Create a new empty scala project. Official documentation

To be able to use sv2chisel within this newly created project, just add the following line to your build.sbt file.

libraryDependencies += "com.ovhcloud" %% "sv2chisel" % "0.1.0-SNAPSHOT"

Create a new Scala main app template using sv2chisel API, here is a template with a few comments to be used as a starting point to translate your (System)Verilog file(s) or project(s):

This template is to be edited to fit your needs and saved under a proper scala hierarchy such as <your-project>/src/main/scala/<MyTranslator.scala>

Translate your code

In your translator project sbt: runMain MyTranslator

Manual chisel project setup

Let's take an example of input verilog

module test #(
    param TEST = 1
    input clock,
    input reset,
    input a,
    output b
  // module body

that would be translated into Chisel

package myproject

import chisel3._
import sv2chisel.helpers.vecconvert._ // assuming module body requires it

class test extends MultiIOModule (
    val TEST: Int = 1
    val a = IO(Input(Bool())
    val b = IO(Output(Bool())
  // module body

We will use this small chisel main app to generate it:

import myproject._
import chisel3.stage._

object MyTestGenerator extends App { 
  (new ChiselStage()).emitVerilog(new test(10))