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.

Packages

Custom derivations (source-pinned)

Attribute	Version	Description
codex	latest release	OpenAI Codex CLI coding agent (upstream prebuilt binary)
opencode	latest release	opencode terminal coding agent (upstream prebuilt binary)
verilator_3	3.926	Verilator 3.x — latest upstream 3.x tag
verilator_4	4.228	Verilator 4.x — latest upstream 4.x tag
systemc_2	2.3.4	SystemC 2.x (accellera-official/systemc, C++14)
systemc_3	3.0.2	SystemC 3.x (accellera-official/systemc, C++17)
vtr_9	9.0.0	Verilog-to-Routing — VPR place-and-route
eqy_0	0.66	YosysHQ equivalence checker
yosys-slang0	—	povik/yosys-slang Yosys plugin
chisel_7	7.x	Chisel 7 with chisel-init, chisel-scala-cli, chisel-mill, chisel-sbt
chipyard_1	1.x	Chipyard SoC framework with chipyard-init
openroad-flow-scripts_26	26Q2	OpenROAD Flow Scripts with openroad-flow-scripts-init
openroad-flow-scripts-wrapper, orfs	—	orfs wrapper for running OpenROAD Flow Scripts with tool PATH setup
hotspot_7	7	HotSpot thermal modeling (uvahotspot/HotSpot)
dramsim3_1	1	DRAMsim3 memory simulator (umd-memsys/DRAMsim3)
mcpat_1	1	McPAT power/area/timing model (HewlettPackard/mcpat)
cacti_6	6.5.0	CACTI 6 cache/memory model
cacti_7	7 pinned	CACTI 7 (HewlettPackard/cacti commit )

Forwarded from nixpkgs (version-tracked)

Attribute	Alias of	Description
verilator_5	basePkgs.verilator	Verilator from nixpkgs
yosys_0, yosys-full_0	basePkgs.yosys	Yosys (full = with GHDL plugin if available)
sv-lang_9	basePkgs.sv-lang_9	LLVM/slang SystemVerilog compiler 9.x
sv-lang_10	basePkgs.sv-lang_10	slang 10.x
sv-lang_11	basePkgs.sv-lang	slang 11.x (latest)
abc_0	basePkgs.abc-verifier	Fixed ABC logic synthesis and verification release
sv2v_0	basePkgs.haskellPackages.sv2v	SystemVerilog-to-Verilog converter
ghdl_6	6.0.0	Fixed GHDL 6 release
nvc_1	basePkgs.nvc	NVC VHDL compiler/simulator
vhdl-ls_0	basePkgs.vhdl-ls	VHDL language server
spike_1	basePkgs.spike	RISC-V ISA simulator
surfer_0	basePkgs.surfer	Surfer waveform viewer
verible_0	basePkgs.verible	SystemVerilog linter and formatter
surelog_1	basePkgs.surelog	SystemVerilog preprocessor and elaborator
uhdm_1	basePkgs.uhdm	Universal Hardware Data Model
openroad_26	basePkgs.openroad	OpenROAD physical design suite
circt	basePkgs.circt	CIRCT / MLIR circuit IR tools
firrtl_1

Package naming convention: unsuffixed custom package attributes track upstream branch HEAD and use unstable-YYYY-MM-DD versions. Numbered attributes are fixed release slots for side-by-side tool versions.

Branch-tracking defaults: abc, aiger, amaranth, aslref, cacti, chipyard, chisel, cocotb, edalize, eqy, firrtl, fusesoc, ghdl, gtkwave, hotspot, icsc, klayout, ndf, openroad, openroad-flow-scripts, pycircuit, spike, sv-lang, slang, sv2v, systemc, verilator, vhdl-ls, vtr, xschem, yosys, and yosys-slang follow upstream branch commits; their numbered companions stay fixed to release-series packages.

Fixed release slots and forwarded aliases include sv-lang_9, sv-lang_10, sv-lang_11, verilator_5, systemc_2, systemc_3, yosys_0, vtr_9, eqy_0, sv2v_0, chisel_7, chipyard_1, hotspot_7, spike_1, vhdl-ls_0, xschem_3, cocotb_2, edalize_0, cacti_6, cacti_7, and pycircuit_6.

Python packages

cocotb and edalize are Python packages. Compose them into a python environment for actual use rather than adding them directly to packages:

pkgs.python3.withPackages (ps: [ pkgs.nixchip.cocotb_2 pkgs.nixchip.edalize_0 ])

Tool groups

Tool groups are symlinkJoin bundles for easy shell composition:

Group	Contents
simulation-tools	verilator, sv-lang, chisel, systemc (3.x), ghdl, nvc, iverilog, gtkwave, surfer, verible, spike, vhdl-ls
formal-tools	yosys-full, sby, eqy, yices, boolector, bitwuzla, cadical, cryptominisat, cvc5, z3, abc, aiger, btor2tools, mcy
fpga-tools	yosys-full, yosys-slang, nextpnr, icestorm, trellis, openfpgaloader, sv2v, vtr, fusesoc, sby
physical-design-tools	openroad, openroad-flow-scripts, openroad-flow-scripts-wrapper, yosys-full, circt, firrtl, klayout, magic-vlsi, netgen-vlsi, (espresso if unfree)
analog-tools	ngspice, xyce, qucs-s, xschem
memory-tools	cacti, dramsim3, mcpat
thermal-tools	hotspot, dramsim3
asic-tools	physical-design-tools + analog-tools + memory-tools + thermal-tools + formal-tools
hardware-tools	simulation-tools + fpga-tools + asic-tools + chipyard + surelog + uhdm
ai-tools	codex, opencode, (claude-code if unfree)

physical-design-tools includes the unfree nixpkgs espresso package only when nixpkgs is imported with allowUnfree = true (or an allowUnfreePredicate admitting it); ai-tools likewise includes the unfree claude-code only when allowed. All three agents are upstream's prebuilt release binaries (claude-code on the latest channel), bumped weekly by scripts/update-ai-agents.sh since nixpkgs' builds lag by months. The flake's own outputs (.#ai-tools, nix develop .#ai) allow claude-code and nothing else.

systemc_2 is not in simulation-tools (which uses systemc_3) to avoid header/library collisions. Use systemc_2 directly as a standalone package or via the versions shell.

Dev shells

Shell	Contents
default / hardware	hardware-tools + general dev tools
simulation	simulation-tools + general dev tools
fpga	fpga-tools + simulation-tools + general dev tools
asic	asic-tools + simulation-tools + general dev tools
ai	ai-tools + general dev tools
versions	verilator_3/4/5, systemc_2/3, sv-lang_9/10/11, yosys_0, yosys-full_0, cacti_6/7

General dev tools included in all shells: bash, git, gnumake, nodejs, python3, shellcheck, shfmt.

Upstream Verilator's canonical GitHub tag history starts at v3.600, so this flake does not publish misleading verilator1 or verilator2 packages.

Workspace-style packages install immutable sources under share/ and provide *-init commands to copy a writable workspace into the current directory.

yosys-slang0 installs slang.so under its own output and provides a yosys-slang wrapper that loads the plugin into the pinned nixpkgs Yosys.

Custom derivation notes

• systemc_2 / systemc_3: built from accellera-official/systemc. Version determines the C++ standard automatically (2.x → C++14, 3.x → C++17).
• vtr_9: built with fetchSubmodules = true (requires Catch2 and sockpp submodules). Parmys, ODIN-II, analytic placement, capnproto, and graphics are disabled for a minimal portable build.
• eqy_0: YosysHQ equivalence checker pinned to upstream v0.66. Builds three .so Yosys plugins and patches Python shebang + template variables.
• icsc: Intel SystemC Compiler built against nixpkgs' LLVM/Clang 18 and protobuf instead of the toolchain upstream's install.sh compiles. ICSC ships no executable: designs link SVC::SCTool through svc_target() from $ICSC_HOME/CMakeLists.txt. The ICSC_HOME variable the dev shells export is exactly the one upstream's CMake files expect; source $ICSC_HOME/setenv.sh also sets LLVM_VER.
• pycircuit: pyCircuit compiler and GFSIM runtime built against nixpkgs' LLVM/MLIR 22 (upstream's exact-patch-version CMake lock is dropped; the llvmPackages_22 input selects the series). pycircuit run finds the toolchain from its own install prefix, but calls cmake, ninja and a C++20 compiler (plus verilator for --target verilog) from PATH.
• xls: upstream's prebuilt linux-x64 release, patched with autoPatchelf rather than built from source (Bazel plus its own LLVM). The DSLX tools are wrapped so import std finds the installed stdlib from any working directory; pass --dslx_stdlib_path (--stdlib_path for dslx_ls) to override it. x86_64-linux only.
• aslref: the ASL reference interpreter alone, built with dune from PTO-ISA's herdtools7 fork (the one pto-spec pins in .aslref-origin) instead of through opam. Point pto-spec at it with make check ASLREF=aslref, or ASLREF=aslref for its test scripts.
• pycircuit_6: the v6.x release, which predates main's ACIR rewrite and ships the older pycc flow (pycircuit emit/build, plus , , and ). The release has no executable, so nixchip wraps and stages the helper scripts its wheel would bundle. calls , , a C++ compiler and from .

Automation

GitHub Actions workflows:

• CI: evaluates the flake and builds the fast package set on Linux.
• Update flake inputs: runs nix flake update weekly and opens or updates a PR.
• Update package pins: runs nix-update -F for custom hardware packages, evaluates nix flake check --no-build, and opens or updates a PR.
• GitHub Pages: publishes a searchable package browser from flake metadata.

Branch-tracking packages always use the unstable-YYYY-MM-DD version format (no tag prefix). Released version pins use standard semver (e.g. 0.62, 26Q2).

The update script (scripts/update-packages.sh) accepts per-package --version-regex constraints via nixchipUpdateFlags to keep packages on their intended major version series (e.g., systemc_2 stays on 2.x).

Set NIXCHIP_UPDATE_HISTORICAL=1 to also update historical version pins (cacti_6, cacti_7, verilator_3, verilator_4) — excluded by default because they are intentionally frozen.

The package browser is generated by scripts/generate-package-index.py from the current flake outputs and the static frontend in site/index.html.