{
  description = "ECP5 toolchain template project";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    litex-overlay.url = "git+https://git.saji.dev/saji/litex-overlay";
  };

  outputs =
    inputs@{ nixpkgs, litex-overlay ... }:
    let
      systems = [
        "x86_64-linux"
        "aarch64-linux"
        "aarch64-darwin"
        "x86_64-darwin"
      ];
      forAllSystems =
        function:
        nixpkgs.lib.genAttrs systems (
          system:
          function (
            import nixpkgs {
              inherit system;
              config.allowUnfree = true;
              overlays = [
                litex-overlay.overlays.default
              ]; # patches, version pins, new pkgs here.
            }
          )
        );
    in
    {
      devShells = forAllSystems (pkgs: {
        default = pkgs.mkShell {
          packages = with pkgs; [
            (python3.withPackages (
              ps: with ps; [
                cocotb
                cocotb-bus
                litex
                litedram
                liteeth
                litescope
                litespi
                liteiclink
                pythondata-cpu-vexriscv
                pythondata-software-compiler_rt
                pythondata-software-picolibc
                amaranth
              ]
            ))
            yosys
            nextpnr
            # simulators
            verilog
            verilator
            # support package
            trellis
            # loader
            openfpgaloader
            ecpdap # easier to poke probes.
          ];
        };
      });
    };
}