{
  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  inputs.bscpkgs.url = "git+https://git.sr.ht/~rodarima/bscpkgs";

  outputs = {self, nixpkgs, ...}@inputs:
  let
    system = "x86_64-linux";
    nixosSystem = import (nixpkgs + "/nixos/lib/eval-config.nix");
    mkRoots = pkgs: list: pkgs.writeText "gcroots.json"
      (builtins.toJSON (map (x: { drv = x; attrs = x.drvAttrs; }) list));
  in {
    #overlay = import ./overlay.nix;
    nixosConfigurations = {
      # The qemu configuration defines a system that runs in the RISC-V
      # architecture, but is build from an x86 host machine.
      qemu = nixosSystem {
        specialArgs = { inherit self; };
        system = "${system}";
        modules = [
          ./configuration.nix
          ./vm.nix
        ];
      };

      # Same, but disable compressed instructions
      qemu-nc = nixosSystem {
        specialArgs = { inherit self; };
        system = "${system}";
        modules = [
          ./configuration.nix
          ./vm.nix
          ./no-compressed.nix
        ];
      };

      # FPGA Lagarto Hun CPU
      lagarto-hun = nixosSystem {
        specialArgs = { inherit self; };
        system = "${system}";
        modules = [
          ./configuration.nix
          ./lagarto-hun.nix
          ./no-compressed.nix
        ];
      };

      # FPGA Lagarto Ox CPU
      lagarto-ox = nixosSystem {
        specialArgs = { inherit self; };
        system = "${system}";
        modules = [
          ./configuration.nix
          ./lagarto-ox.nix
          ./no-compressed.nix
        ];
      };
    };

    # A development shell with QEMU ready to boot the RISC-V system in an x86
    # machine.
    devShells.x86_64-linux.qemu-lagarto-hun =
    let
      nixosconf = self.nixosConfigurations.qemu-nc;
      syspkgs = nixosconf.pkgs;
      toplevel = nixosconf.config.system.build.toplevel;
    in syspkgs.mkShell {
      pname = "qemu-shell";
      nativeBuildInputs = with syspkgs; [ qemu e2fsprogs ];
      # Here we tell the run script where to find the system
      NIXOS_SYSTEM_TOPLEVEL = toplevel;
      OPENSBI = syspkgs.opensbi-uboot;
    };

    devShells.x86_64-linux.lagarto-hun =
    let
      nixosconf = self.nixosConfigurations.lagarto-hun;
      syspkgs = nixosconf.pkgs;
      build = nixosconf.config.system.build;
    in syspkgs.mkShell {
      pname = "lagarto-hun-shell";
      COMMIT = if self ? rev then self.rev else "dirty";
      TOPLEVEL = build.toplevel;
      OPENSBI = syspkgs.opensbi;
      KERNEL = build.kernel;
      INITRD = build.initialRamdisk;
      ROOTFS = build.sdImage;
      UBOOT_ENV = syspkgs.uboot-env;
      shellHook = ''
        echo "Here are the current system pieces:"
        echo " COMMIT    = $COMMIT"
        echo " TOPLEVEL  = $TOPLEVEL"
        echo " KERNEL    = $KERNEL"
        echo " OPENSBI   = $OPENSBI"
        echo " INITRD    = $INITRD"
        echo " ROOTFS    = $ROOTFS"
        echo " UBOOT_ENV = $UBOOT_ENV"
      '';
    };

    devShells.x86_64-linux.lagarto-ox =
    let
      nixosconf = self.nixosConfigurations.lagarto-ox;
      syspkgs = nixosconf.pkgs;
      build = nixosconf.config.system.build;
    in syspkgs.mkShell rec {
      pname = "lagarto-ox-shell";
      COMMIT = if self ? rev then self.rev else "dirty";
      TOPLEVEL = build.toplevel;
      OPENSBI = syspkgs.opensbi;
      KERNEL = build.kernel;
      INITRD = build.initialRamdisk;
      ROOTFS = build.sdImage;
      UBOOT_ENV = syspkgs.uboot-env;
      BITSTREAM = syspkgs.bitstream;
      BOOTROM = syspkgs.bootrom;
      GCROOT = mkRoots syspkgs [
        syspkgs.stdenv KERNEL OPENSBI syspkgs.riscv-tools
      ];
      shellHook = ''
        echo "Here are the current system pieces:"
        echo " COMMIT    = $COMMIT"
        echo " TOPLEVEL  = $TOPLEVEL"
        echo " KERNEL    = $KERNEL"
        echo " OPENSBI   = $OPENSBI"
        echo " INITRD    = $INITRD"
        echo " ROOTFS    = $ROOTFS"
        echo " UBOOT_ENV = $UBOOT_ENV"
        echo " BITSTREAM = $BITSTREAM"
        echo " BOOTROM   = $BOOTROM"
        echo " GCROOT    = $GCROOT"
      '';
    };

    devShells.x86_64-linux.lagarto-ox-rd =
    let
      nixosconf = self.nixosConfigurations.lagarto-ox;
      syspkgs = nixosconf.pkgs;
    in self.outputs.devShells.x86_64-linux.lagarto-ox.overrideAttrs (old:{
        TOPLEVEL = "";
        ROOTFS = "";
        GCROOT = mkRoots syspkgs [ syspkgs.stdenv old.OPENSBI ];
      });

    devShells.x86_64-linux.default =
      self.outputs.devShells.x86_64-linux.lagarto-ox-rd;
  };
}