nixchip

nixchip is a Nix flake for open hardware development. Hardware packages live under pkgs/; general development tools such as Python, Node.js, Git, Make, and shell linters come directly from nixpkgs in the dev shells.

Quick start

nix develop github:helcel-net/nixchip              # full hardware toolbox
nix develop github:helcel-net/nixchip#simulation   # simulators + waveform viewers
nix develop github:helcel-net/nixchip#fpga         # synthesis + place-and-route
nix develop github:helcel-net/nixchip#asic         # physical design + analog + formal
nix develop github:helcel-net/nixchip#ai         # claude-code + codex + opencode
nix develop github:helcel-net/nixchip#versions     # side-by-side verilator_3/4/5, systemc_2/3, etc.

Every shell exports ${PKGNAME}_HOME, ${PKGNAME}_BIN, ${PKGNAME}_LIB, and ${PKGNAME}_INCLUDE for every individual package in the collection, regardless of which packages are in packages =. See Environment variables.

Use as a flake input

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    nixchip.url = "github:helcel-net/nixchip";
  };

  outputs =
    { nixpkgs, nixchip, ... }:
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs {
        inherit system;
        overlays = [ nixchip.overlays.default ];
      };
    in
    {
      devShells.${system}.default = pkgs.mkShellNoCC {
        packages = [
          pkgs.nixchip.hardware-tools
          pkgs.nixchip.verilator_4
        ];
        shellHook = nixchip.lib.mkNixchipVarsHook pkgs.nixchip;
      };
    };
}

The overlay exports packages under both pkgs.nixchip.* and top-level package names such as pkgs.verilator_4.

Binary caches

CI pushes every build to the nixchip0 Cachix cache, declared in this flake's nixConfig — running any nix command with --accept-flake-config (or accept-flake-config = true in nix.conf) substitutes it automatically.

To actually get cache hits, consume nixchip's packages built against nixchip's own nixpkgs pin. Overriding it rewrites every derivation hash and forces full source rebuilds:

# Cache-friendly: share nixchip's pin.
inputs.nixchip.url = "github:helcel-net/nixchip";
inputs.nixpkgs.follows = "nixchip/nixpkgs";

# Cache-hostile: every nixchip package rebuilds from source.
# inputs.nixchip.inputs.nixpkgs.follows = "nixpkgs";

If you must keep your own nixpkgs pin, use a second, un-overridden nixchip input for the heavy EDA tools and your own pin for everything else.

For non-hardware tooling, use nixpkgs directly:

pkgs.mkShellNoCC {
  packages = [
    pkgs.nixchip.hardware-tools
    pkgs.python3
    pkgs.nodejs
    pkgs.shellcheck
  ];
}

Use from nix-shell

Create a shell.nix:

let
  nixchip = builtins.getFlake "github:helcel-net/nixchip";
  system = builtins.currentSystem;
  pkgs = nixchip.legacyPackages.${system};
in
pkgs.mkShellNoCC {
  packages = [
    pkgs.nixchip.hardware-tools
  ];
  shellHook = nixchip.lib.mkNixchipVarsHook pkgs.nixchip;
}

Then run:

nix-shell --experimental-features 'nix-command flakes'

Environment variables

Every dev shell (including downstream shells that call mkNixchipVarsHook) exports four variables per package:

Variable	Value
PKGNAME_HOME	Nix store path (package root)
PKGNAME_BIN	$PKGNAME_HOME/bin
PKGNAME_LIB	$PKGNAME_HOME/lib
PKGNAME_INCLUDE	$PKGNAME_HOME/include

Package name to env prefix: hyphens become underscores, all uppercase.

Examples:

verilator_4       → VERILATOR_4_HOME / VERILATOR_4_BIN / VERILATOR_4_LIB / VERILATOR_4_INCLUDE
systemc_2         → SYSTEMC_2_HOME / SYSTEMC_2_BIN / SYSTEMC_2_LIB / SYSTEMC_2_INCLUDE
sv-lang_9         → SV_LANG_9_HOME / SV_LANG_9_BIN / ...
yosys-full_0      → YOSYS_FULL_0_HOME / YOSYS_FULL_0_BIN / ...
gem5              → GEM5_HOME / ...
qucs-s_25         → QUCS_S_25_HOME / ...

Tool-group bundles (*-tools) and Python-only packages (cocotb, edalize) are excluded from the export because they are meant to be used differently. The AI agents (codex, opencode) are excluded too: codex reads CODEX_HOME as its writable config directory.

mkNixchipVarsHook for downstream flakes

nixchip.lib.mkNixchipVarsHook takes a pkgs.nixchip attribute set and returns a shell hook string. Wire it in as shown in the flake input example above. The hook is evaluated at evaluation time — no runtime lookups occur.

This is the beginning of the README. Read the rest at the original. Read the full README ↗