Setting Up Verible for Verilog with Neovim

I have been using Vivado for moss RTL development, which, despite its notoriously large install size, offers a fairly decent developer experience.

Or maybe I have just been using it for too long. I’m not sure I would have said this a few months ago.

However, I still prefer to write Verilog in Neovim, as it allows me to use vim motions, as well as switch between RTL and software code without changing my workflow. For most languages, I leverage Neovim’s Language Server Protocol (LSP) support for linting, formatting, auto-completion, and compiler diagnostics. I had been missing the same level of support for Verilog, but noticed that nvim-lspconfig listed a few different options. One of the most mature options is Verible, which is developed under the CHIPS Alliance.

Setup is pretty straightforward and mirrors other language server configurations. I still use an init.vim configuration script rather than init.lua, but the setup looks largely the same.

init.vim (snippet)

lua <<EOF
require('lspconfig').verible.setup{
  cmd = {'verible-verilog-ls', '--rules_config_search'},
}
EOF

autocmd BufWritePost *.v lua vim.lsp.buf.format({ async = false })

verible-verilog-ls is the language server component of the Verible tool suite. You can find additional configuraion options in the Verible and nvim-lspconfig documentation. The primary adjustments being made to the default setup are that we are supplying a flag (--rules_config_search) and specifying that we want formatting (vim.lsp.buf.format) to run automatically after saving Verilog (*.v) files.

The next time I opened Neovim, I was able to auto-format all existing RTL files on save. I also was presented with inline hints, such as the ones shown below.

Neovim buffer with linter errors shown for explicit-parameter-storage-type and always_comb rules.

While this is helpful, Verible, as well as many of the other language server options, is designed primarily for SystemVerilog. Because SystemVerilog is a superset of Verilog, many of the linter rules suggest changes that are not valid in Verilog, such as the use of keywords like always_comb (you can find a full list of linter rules here). Given the sample size of the existing moss RTL, I was able to put together a Verible linting configuration that eliminated these issues.

.rules.verible_lint

parameter-name-style=localparam_style:ALL_CAPS
-always-comb
-explicit-parameter-storage-type
-unpacked-dimensions-range-ordering

Because we supplied the --rules_config_search flag, verible-verilog-ls will automatically search for a rules file with name .rules.verible_lint in parent directories and apply it to the current file. This is especially useful in the case of our Neovim setup where the path to the rules file may differ between projects, so supplying a path via --rules_config <path> in our config would be brittle. Reopening Neovim revealed that the rules file was in fact being honored.

Note: you can test your linter rules config by invoking verible-verilog-lint <path> --rules_config_search directly.

The same Neovim buffer, now devoid of errors.

I am sure that my setup will continue to evolve over time, but my development workflow has already been significantly improved, despite still having to open Vivado to run simulation, synthesis, and implementation (place & route). Given that interfacing with Vivado can be done using tcl commands, I am planning to move towards not using the UI at all and triggering all workflows from Neovim. Coming to logic design from a software engineering background, I believe that I have a unique opportunity to push forward improved developer experience in the space. Documenting how to leverage some of the awesome existing open source tooling is a small, but important first step, and I’ll make sure to continue to write posts as my workflow evolves over time!

If you’re interested in keeping up with my three year chip design journey, subscribe to the RSS feed for this blog, and tune in for my ~weekly livestreams. As always, if you have feedback, questions, or just want to chat, feel free to reach out to @hasheddan on any of the platforms listed on the home page.