diff --git a/.actrc b/.actrc
new file mode 100644
index 0000000..d270424
--- /dev/null
+++ b/.actrc
@@ -0,0 +1 @@
+-P ubuntu-latest=catthehacker/ubuntu:runner-latest
diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..82ebf5c
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,26 @@
+# Editor configuration, see http://editorconfig.org
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+charset = utf-8
+indent_style = space
+indent_size = 2
+
+[*.md]
+max_line_length = off
+trim_trailing_whitespace = false
+indent_size = unset
+
+[*.py]
+indent_size = 4
+
+[*.sh]
+indent_style = space
+indent_size = 4
+binary_next_line = true
+switch_case_indent = true
+space_redirects = false
+keep_padding = true
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..6834fef
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,41 @@
+name: Run ATX-Raspi tests
+on:
+  pull_request:
+  push:
+  workflow_dispatch:
+jobs:
+  flake:
+    name: Run Nix flake checks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Initialize Nix store paths
+        run: |
+          sudo mkdir -p /nix/store
+          sudo chmod -R 777 /nix
+      # https://github.com/cachix/install-nix-action/issues/56#issuecomment-1030697681
+      - name: Configure Nix store cache
+        uses: actions/cache@v4
+        with:
+          key: ${{ runner.os }}-${{ runner.arch }}-nix-store
+          # See https://github.com/actions/cache/pull/726 and
+          # https://github.com/actions/cache/issues/494 for caveats on negative
+          # patterns.
+          path: |
+            /nix/store/**
+            /nix/var/nix/*/*
+            /nix/var/nix/db/*
+            /nix/var/nix/db/*/**
+            !/nix/var/nix/daemon-socket/socket
+            !/nix/var/nix/userpool/*
+            !/nix/var/nix/gc.lock
+            !/nix/var/nix/db/big-lock
+            !/nix/var/nix/db/reserved
+      - name: Install Nix
+        uses: cachix/install-nix-action@v31
+        with:
+          extra_nix_config: |
+            system-features = benchmark big-parallel kvm nixos-test uid-range
+      - name: Run Nix flake checks
+        run: |
+          nix flake check -L
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6688664
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,13 @@
+# VM disk images
+*.qcow2
+
+# Nix build results
+result
+result-*
+repl-result-*
+
+# NixOS test driver REPL history
+.nixos-test-history
+
+# Binary executable.
+/nix/pkgs/gpiosimtest/gpiosimtest
diff --git a/doc/nixos-modules.md b/doc/nixos-modules.md
new file mode 100644
index 0000000..b494496
--- /dev/null
+++ b/doc/nixos-modules.md
@@ -0,0 +1,206 @@
+## services\.atx-raspi-shutdown\.enable
+
+
+
+Whether to enable the ATX-Raspi shutdown daemon\.
+
+
+
+*Type:*
+boolean
+
+
+
+*Default:*
+` false `
+
+
+
+*Example:*
+` true `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
+
+## services\.atx-raspi-shutdown\.package
+
+
+
+Package providing the ATX-Raspi daemon\.
+
+
+
+*Type:*
+package
+
+
+
+*Default:*
+` <derivation atx-raspi-shutdownirq> `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
+
+## services\.atx-raspi-shutdown\.chip
+
+The path to the GPIO chip\.
+
+
+
+*Type:*
+null or absolute path
+
+
+
+*Default:*
+` null `
+
+
+
+*Example:*
+` "/dev/gpiochip42" `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
+
+## services\.atx-raspi-shutdown\.implementation
+
+
+
+GPIO daemon implementation\.  “irq” selects the
+edge-triggered Python implementation\.  “check” selects
+the polling-based shell implementation\.
+
+
+
+*Type:*
+one of “check”, “irq”
+
+
+
+*Default:*
+` "irq" `
+
+
+
+*Example:*
+` "check" `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
+
+## services\.atx-raspi-shutdown\.pins\.boot
+
+
+
+Pin on ` chip ` to set high upon ATX-Raspi
+service startup\.
+
+
+
+*Type:*
+null or (unsigned integer, meaning >=0)
+
+
+
+*Default:*
+` null `
+
+
+
+*Example:*
+` 8 `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
+
+## services\.atx-raspi-shutdown\.pins\.shutdown
+
+
+
+Pin on ` chip ` to watch for the shutdown or
+reboot button press\.
+
+
+
+*Type:*
+null or (unsigned integer, meaning >=0)
+
+
+
+*Default:*
+` null `
+
+
+
+*Example:*
+` 7 `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
+
+## services\.atx-raspi-shutdown\.pulses\.reboot
+
+
+
+Minimum duration of high state on
+` pins.shutdown ` to trigger reboot\.
+
+
+
+*Type:*
+null or floating point number
+
+
+
+*Default:*
+` null `
+
+
+
+*Example:*
+` 0.2 `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
+
+## services\.atx-raspi-shutdown\.pulses\.shutdown
+
+
+
+Minimum duration of high state on
+` pins.shutdown ` to trigger shutdown\.
+
+
+
+*Type:*
+null or floating point number
+
+
+
+*Default:*
+` null `
+
+
+
+*Example:*
+` 0.6 `
+
+*Declared by:*
+ - [flake\.nix](/flake.nix)
+
+
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..c24a65b
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,103 @@
+{
+  "nodes": {
+    "devshell": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1741473158,
+        "narHash": "sha256-kWNaq6wQUbUMlPgw8Y+9/9wP0F8SHkjy24/mN3UAppg=",
+        "owner": "numtide",
+        "repo": "devshell",
+        "rev": "7c9e793ebe66bcba8292989a68c0419b737a22a0",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "devshell",
+        "type": "github"
+      }
+    },
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      },
+      "locked": {
+        "lastModified": 1741352980,
+        "narHash": "sha256-+u2UunDA4Cl5Fci3m7S643HzKmIDAe+fiXrLqYsR2fs=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "f4330d22f1c5d2ba72d3d22df5597d123fdb60a9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1742669843,
+        "narHash": "sha256-G5n+FOXLXcRx+3hCJ6Rt6ZQyF1zqQ0DL0sWAMn2Nk0w=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "1e5b653dff12029333a6546c11e108ede13052eb",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-lib": {
+      "locked": {
+        "lastModified": 1740877520,
+        "narHash": "sha256-oiwv/ZK/2FhGxrCkQkB83i7GnWXPPLzoqFHpDD3uYpk=",
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "rev": "147dee35aab2193b174e4c0868bd80ead5ce755c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "devshell": "devshell",
+        "flake-parts": "flake-parts",
+        "nixpkgs": "nixpkgs",
+        "treefmt-nix": "treefmt-nix"
+      }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1742370146,
+        "narHash": "sha256-XRE8hL4vKIQyVMDXykFh4ceo3KSpuJF3ts8GKwh5bIU=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "adc195eef5da3606891cedf80c0d9ce2d3190808",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..1e5ee45
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,83 @@
+{
+  description = "Description for the project";
+
+  inputs = {
+    devshell.url = "github:numtide/devshell";
+    devshell.inputs.nixpkgs.follows = "nixpkgs";
+
+    flake-parts.url = "github:hercules-ci/flake-parts";
+
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+    treefmt-nix.inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs = inputs:
+    inputs.flake-parts.lib.mkFlake {inherit inputs;} ({
+      inputs,
+      moduleWithSystem,
+      self,
+      ...
+    }: {
+      systems = [
+        "aarch64-darwin"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "x86_64-linux"
+      ];
+
+      imports = [
+        inputs.devshell.flakeModule
+        inputs.treefmt-nix.flakeModule
+
+        ./nix/checks.nix
+        ./nix/devshells.nix
+        ./nix/nixos-modules.nix
+        ./nix/packages.nix
+      ];
+
+      flake = {
+        nixosConfigurations = {
+          default = inputs.nixpkgs.lib.nixosSystem {
+            modules = [
+              self.nixosModules.atx-raspi
+              {
+                boot.isContainer = true;
+                fileSystems."/".fsType = "tmpfs";
+                nixpkgs.hostPlatform = "x86_64-linux";
+                system.stateVersion = "24.11";
+              }
+            ];
+          };
+        };
+      };
+
+      perSystem = {
+        config,
+        lib,
+        ...
+      }: {
+        apps = lib.mapAttrs (lib.const (lib.getAttr "flakeApp")) config.devShells;
+
+        treefmt = {config, ...}: {
+          flakeFormatter = true;
+          projectRootFile = "flake.nix";
+
+          programs = {
+            alejandra.enable = true;
+            gofumpt.enable = true;
+            ruff.enable = true;
+            shellcheck.enable = true;
+            shfmt.enable = true;
+          };
+
+          settings.formatter = lib.mkIf config.programs.shfmt.enable {
+            # Empty out the CLI options list so that `shfmt` uses the settings
+            # from `.editorconfig`.
+            shfmt.options = lib.mkForce [];
+          };
+        };
+      };
+    });
+}
diff --git a/nix/checks.nix b/nix/checks.nix
new file mode 100644
index 0000000..c9aa181
--- /dev/null
+++ b/nix/checks.nix
@@ -0,0 +1,116 @@
+{self, ...}: {
+  perSystem = {
+    config,
+    lib,
+    pkgs,
+    ...
+  }: {
+    checks = {
+      default = config.checks.atx-raspi;
+
+      atx-raspi = pkgs.nixosTest {
+        name = "atx-raspi-shutdown";
+        nodes = let
+          common = {pkgs, ...}: {
+            imports = [self.nixosModules.default];
+
+            boot.kernelModules = ["gpio-sim"];
+
+            environment.systemPackages = with pkgs; [
+              curl
+              jq
+            ];
+
+            security.polkit.debug = true;
+            security.polkit.enable = true;
+
+            services.atx-raspi-shutdown.enable = true;
+
+            systemd.services.gpiosimtest = {
+              wantedBy = ["multi-user.target"];
+              environment.PORT = "8080";
+              serviceConfig = {
+                ExecStart = lib.getExe config.packages.gpiosimtest;
+              };
+            };
+
+            systemd.services.atx-raspi-shutdown = {
+              wantedBy = lib.mkForce []; # Need to start manually.
+              requires = ["gpiosimtest.service"];
+              after = ["gpiosimtest.service"];
+              environment.ATX_RASPI_DRY_RUN = "1";
+            };
+          };
+        in {
+          check = {...}: {
+            imports = [common];
+            services.atx-raspi-shutdown.implementation = "check";
+          };
+
+          irq = {...}: {
+            imports = [common];
+            services.atx-raspi-shutdown.implementation = "irq";
+          };
+        };
+        testScript = {nodes, ...}: let
+          checkURL = "http://localhost:${nodes.check.systemd.services.gpiosimtest.environment.PORT}";
+          irqURL = "http://localhost:${nodes.irq.systemd.services.gpiosimtest.environment.PORT}";
+        in ''
+          import time
+
+          from typing import Optional
+
+          def systemctl_succeed(m: Machine, q: str, user: Optional[str] = None) -> str:
+            user_desc = "root"
+            if user is not None:
+              user_desc = user
+            with m.nested(f"command `systemctl {q}` must succeed as {user_desc}"):
+              (status, output) = m.systemctl(q, user)
+
+              if status != 0:
+                  m.log(f"output: {output}")
+                  raise Exception(f"command `systemctl {q}` failed as {user_desc} (exit code {status})")
+
+              return output
+
+          start_all()
+
+          check.succeed("modprobe gpio_sim 1>&2")
+          check.succeed("lsmod | grep gpio_sim 1>&2")
+
+          check.wait_for_unit("dbus.service")
+
+          systemctl_succeed(check, "cat polkit.service 1>&2")
+          systemctl_succeed(check, "cat atx-raspi-shutdown.service 1>&2")
+
+          systemctl_succeed(irq, "cat polkit.service 1>&2")
+          systemctl_succeed(irq, "cat atx-raspi-shutdown.service 1>&2")
+
+          check.wait_for_unit("gpiosimtest.service")
+          check_chip = check.succeed("curl ${checkURL}/devpath | jq --raw-output '.data.devpath'").strip()
+          systemctl_succeed(check, f"set-environment ATX_RASPI_CHIP={check_chip}")
+
+          irq.wait_for_unit("gpiosimtest.service")
+          irq_chip = irq.succeed("curl ${irqURL}/devpath | jq --raw-output '.data.devpath'").strip()
+          systemctl_succeed(irq, f"set-environment ATX_RASPI_CHIP={irq_chip}")
+
+          systemctl_succeed(check, "start atx-raspi-shutdown.service")
+          check.wait_for_unit("atx-raspi-shutdown.service")
+          check.wait_until_succeeds("test $(curl ${checkURL}/line/8/level | jq --raw-output '.data.level') = 1")
+          check.wait_until_succeeds("curl -X PUT ${checkURL}/line/7/pull/up | jq 1>&2")
+          time.sleep(5)
+          check.wait_until_succeeds("curl -X PUT ${checkURL}/line/7/pull/down | jq 1>&2")
+          check.wait_until_succeeds(f"journalctl --grep='SHUTDOWN request on chip {check_chip}'")
+
+          systemctl_succeed(irq, "start atx-raspi-shutdown.service")
+          irq.wait_for_unit("atx-raspi-shutdown.service")
+          irq.wait_until_succeeds("test $(curl ${irqURL}/line/8/level | jq --raw-output '.data.level') = 1")
+          irq.wait_until_succeeds("curl -X PUT ${irqURL}/line/7/pull/up | jq 1>&2")
+          time.sleep(5)
+          irq.wait_until_succeeds("curl -X PUT ${irqURL}/line/7/pull/down | jq 1>&2")
+          check.wait_until_succeeds(f"journalctl --grep='SHUTDOWN request on chip {irq_chip}'")
+        '';
+      };
+    };
+  };
+}
diff --git a/nix/devshells.nix b/nix/devshells.nix
new file mode 100644
index 0000000..aa3099f
--- /dev/null
+++ b/nix/devshells.nix
@@ -0,0 +1,50 @@
+{
+  perSystem = {
+    config,
+    lib,
+    pkgs,
+    ...
+  }: {
+    devShells = {
+      default = config.devShells.atx-raspi;
+    };
+
+    devshells = {
+      atx-raspi = {extraModulesPath, ...}: {
+        imports = ["${extraModulesPath}/language/go.nix"];
+
+        commands =
+          [
+            {
+              package = pkgs.act;
+            }
+
+            {
+              package = pkgs.libgpiod;
+            }
+
+            {
+              package = config.treefmt.build.wrapper;
+            }
+
+            {
+              name = "mkoptdocs";
+              command = ''
+                cd "$(git rev-parse --show-cdup)" || exit
+                while read -r out_path; do
+                  install -Dm0644 "$out_path" ./doc/nixos-modules.md
+                done < <(nix build "$@" --no-link --print-out-paths '.#docs')
+              '';
+              help = "Build NixOS module options documentation";
+            }
+          ]
+          ++ lib.pipe config.packages [
+            (lib.flip builtins.removeAttrs ["default"])
+            (builtins.attrValues)
+            (lib.filter (package: package ? meta.mainProgram))
+            (map (package: {inherit package;}))
+          ];
+      };
+    };
+  };
+}
diff --git a/nix/nixos-modules.nix b/nix/nixos-modules.nix
new file mode 100644
index 0000000..89453be
--- /dev/null
+++ b/nix/nixos-modules.nix
@@ -0,0 +1,236 @@
+{
+  self,
+  moduleWithSystem,
+  ...
+}: {
+  flake = {
+    nixosModules = {
+      default = self.nixosModules.atx-raspi;
+
+      atx-raspi = moduleWithSystem (
+        {config, ...} @ perSystem: {
+          config,
+          lib,
+          options,
+          ...
+        }: let
+          inherit (lib) mkOption types;
+          cfg = config.services.atx-raspi-shutdown;
+          opts = options.services.atx-raspi-shutdown;
+          description = "ATX-Raspi shutdown daemon";
+          polkitEnabled = config.security.polkit.enable;
+          wrap = lib.replaceStrings ["\n"] [" "];
+        in {
+          options = {
+            services = {
+              atx-raspi-shutdown = {
+                enable = lib.mkEnableOption "the ${description}";
+
+                implementation = mkOption {
+                  type = types.enum ["check" "irq"];
+                  default = "irq";
+                  example = "check";
+                  description = ''
+                    GPIO daemon implementation.  "irq" selects the
+                    edge-triggered Python implementation.  "check" selects
+                    the polling-based shell implementation.
+                  '';
+                };
+
+                package = mkOption {
+                  type = types.package;
+                  default = perSystem.config.packages."atx-raspi-shutdown${cfg.implementation}";
+                  description = ''
+                    Package providing the ATX-Raspi daemon.
+                  '';
+                };
+
+                chip = mkOption {
+                  type = types.nullOr types.path;
+                  default = null;
+                  example = "/dev/gpiochip42";
+                  description = ''
+                    The path to the GPIO chip.
+                  '';
+                };
+
+                pins = {
+                  shutdown = mkOption {
+                    type = types.nullOr types.ints.unsigned;
+                    default = null;
+                    example = 7;
+                    description = ''
+                      Pin on {option}`chip` to watch for the shutdown or
+                      reboot button press.
+                    '';
+                  };
+
+                  boot = mkOption {
+                    inherit (opts.pins.shutdown) type;
+                    default = null;
+                    example = 8;
+                    description = ''
+                      Pin on {option}`chip` to set high upon ATX-Raspi
+                      service startup.
+                    '';
+                  };
+                };
+
+                pulses = {
+                  reboot = mkOption {
+                    type = types.nullOr types.float;
+                    default = null;
+                    example = 0.2;
+                    description = ''
+                      Minimum duration of high state on
+                      {option}`pins.shutdown` to trigger reboot.
+                    '';
+                  };
+
+                  shutdown = mkOption {
+                    inherit (opts.pulses.reboot) type;
+                    default = null;
+                    example = 0.6;
+                    description = ''
+                      Minimum duration of high state on
+                      {option}`pins.shutdown` to trigger shutdown.
+                    '';
+                  };
+                };
+              };
+            };
+          };
+
+          config = lib.mkIf cfg.enable {
+            systemd.services.atx-raspi-shutdown = lib.const {
+              imports = [
+                (lib.mkIf polkitEnabled {
+                  #serviceConfig.DynamicUser = true;
+                })
+              ];
+
+              description = "The ${description}";
+
+              wantedBy = ["basic.target"];
+
+              environment =
+                lib.flip lib.pipe [
+                  (lib.filterAttrs (_: value: value != null))
+                  (lib.mapAttrs' (name: value: {
+                    inherit value;
+                    name = "ATX_RASPI_${lib.toUpper name}";
+                  }))
+                ] {
+                  inherit (cfg) chip;
+                  boot_pin = cfg.pins.boot;
+                  shutdown_pin = cfg.pins.shutdown;
+                  pulse_min = cfg.pulses.reboot;
+                  pulse_max = cfg.pulses.shutdown;
+                };
+
+              serviceConfig = {
+                UMask = "0027";
+
+                Restart = "always";
+                RestartSec = 3;
+
+                BindPaths =
+                  [
+                    #"/run/dbus/system_bus_socket"
+                  ]
+                  ++ lib.optional (cfg.chip != null) cfg.chip;
+
+                ExecStart = lib.getExe cfg.package;
+
+                # Security settings
+                CapabilityBoundingSet = [""];
+                DevicePolicy = "closed";
+                DeviceAllow = "char-gpiochip";
+                LockPersonality = true;
+                MemoryDenyWriteExecute = true;
+                NoNewPrivileges = true;
+                PrivateDevices = false;
+                PrivateIPC = true;
+                PrivateTmp = true;
+                ProcSubset = "pid";
+                ProtectClock = true;
+                ProtectControlGroups = true;
+                ProtectHome = true;
+                ProtectHostname = true;
+                ProtectKernelLogs = true;
+                ProtectKernelModules = true;
+                ProtectKernelTunables = true;
+                ProtectProc = "invisible";
+                ProtectSystem = "strict";
+                RemoveIPC = true;
+                RestrictAddressFamilies = [
+                  "AF_INET"
+                  "AF_INET6"
+                  "AF_NETLINK"
+                  "AF_UNIX"
+                ];
+                RestrictNamespaces = true;
+                RestrictRealtime = true;
+                RestrictSUIDSGID = true;
+                SystemCallArchitectures = "native";
+                SystemCallFilter = [
+                  "@system-service @resources"
+                  "~@privileged"
+                ];
+              };
+            };
+
+            assertions = let
+              noNullAttrValues = attrs: lib.all (x: x != null) (builtins.attrValues attrs);
+            in [
+              {
+                assertion = (noNullAttrValues cfg.pins) -> (cfg.pins.boot != cfg.pins.shutdown);
+                message = wrap ''
+                  atx-raspi: boot pin and shutdown pin must be distinct
+                '';
+              }
+
+              {
+                assertion = (noNullAttrValues cfg.pulses) -> (cfg.pulses.reboot > cfg.pulses.shutdown);
+                message = wrap ''
+                  atx-raspi: shutdown pulse must be longer than reboot pulse
+                  (reboot pulse is ${toString cfg.pulses.reboot}, shutdown
+                  pulse is ${toString cfg.pulses.poweroff})
+                '';
+              }
+            ];
+
+            warnings = lib.optional (!polkitEnabled) (wrap ''
+              atx-raspi: `security.polkit.enable` is set to `false`; running
+              the GPIO daemon as `root`.
+            '');
+
+            security.polkit.extraConfig = ''
+              // Permit ATX-Raspi service users to power off and reboot
+              polkit.addRule(function(action, subject) {
+                if (
+                  (
+                       action.id == "org.freedesktop.login1.power-off"
+                    || action.id == "org.freedesktop.login1.power-off-multiple-sessions"
+                    || action.id == "org.freedesktop.login1.power-off-ignore-inhibit"
+                    || action.id == "org.freedesktop.login1.reboot"
+                    || action.id == "org.freedesktop.login1.reboot-multiple-sessions"
+                    || action.id == "org.freedesktop.login1.reboot-ignore-inhibit"
+                    || action.id == "org.freedesktop.login1.suspend"
+                    || action.id == "org.freedesktop.login1.suspend-multiple-sessions"
+                    || action.id == "org.freedesktop.login1.suspend-ignore-inhibit"
+                    || action.id == "org.freedesktop.login1.hibernate"
+                    || action.id == "org.freedesktop.login1.hibernate-multiple-sessions"
+                    || action.id == "org.freedesktop.login1.hibernate-ignore-inhibit"
+                  ) && subject.user == "${config.systemd.services.atx-raspi-shutdown.serviceConfig.User or "atx-raspi-shutdown"}"
+                ) {
+                  return polkit.Result.YES;
+                }
+              });
+            '';
+          };
+        }
+      );
+    };
+  };
+}
diff --git a/nix/packages.nix b/nix/packages.nix
new file mode 100644
index 0000000..9fcfed3
--- /dev/null
+++ b/nix/packages.nix
@@ -0,0 +1,81 @@
+{self, ...}: {
+  perSystem = {
+    config,
+    pkgs,
+    system,
+    ...
+  }: {
+    packages = {
+      default = config.packages.atx-raspi-shutdownirq;
+
+      atx-raspi-shutdownirq = pkgs.callPackage ({
+        writers,
+        python3,
+      }:
+        writers.makeScriptWriter {
+          inherit (python3.withPackages (p: [p.libgpiod])) interpreter;
+        } "/bin/atx-raspi-shutdownirq" (builtins.readFile "${self}/shutdownirq.py")) {};
+
+      atx-raspi-shutdowncheck = pkgs.callPackage ({
+        coreutils,
+        libgpiod,
+        lib,
+        writers,
+      }:
+        writers.writeBashBin "atx-raspi-shutdowncheck" {
+          makeWrapperArgs = [
+            "--prefix"
+            "PATH"
+            ":"
+            (lib.makeBinPath [coreutils libgpiod])
+          ];
+        } (builtins.readFile "${self}/shutdowncheck.sh")) {};
+
+      docs = pkgs.callPackage ({
+        nixosOptionsDoc,
+        lib,
+        eval,
+      }:
+        (nixosOptionsDoc {
+          options = {
+            inherit (eval.options.services) atx-raspi-shutdown;
+          };
+
+          # Default is currently "appendix".
+          documentType = "none";
+
+          warningsAreErrors = true;
+
+          transformOptions = let
+            ourPrefix = "${toString self}/";
+            moduleSource = "flake.nix";
+            link = {
+              url = "/${moduleSource}";
+              name = moduleSource;
+            };
+          in
+            opt:
+              opt
+              // {
+                visible = opt.visible && (lib.any (lib.hasPrefix ourPrefix) opt.declarations);
+                declarations = map (decl:
+                  if lib.hasPrefix ourPrefix decl
+                  then link
+                  else decl)
+                opt.declarations;
+              };
+        })
+        .optionsCommonMark) {
+        eval = self.nixosConfigurations.default.extendModules {
+          modules = [
+            {
+              nixpkgs.hostPlatform = system;
+            }
+          ];
+        };
+      };
+
+      gpiosimtest = pkgs.callPackage ./pkgs/gpiosimtest {};
+    };
+  };
+}
diff --git a/nix/pkgs/gpiosimtest/default.nix b/nix/pkgs/gpiosimtest/default.nix
new file mode 100644
index 0000000..be82aa8
--- /dev/null
+++ b/nix/pkgs/gpiosimtest/default.nix
@@ -0,0 +1,13 @@
+{buildGoModule}:
+buildGoModule {
+  pname = "gpiosimtest";
+  version = "0.1.0";
+  src = ./.;
+  vendorHash = "sha256-wufUG34GPZLdcuhVls06o3uiVf0wYUVjFQOdbYbZ5pg=";
+  tags = ["nomsgpack"];
+  meta = {
+    description = "GPIO chip simulation API";
+    homepage = "https://github.com/LowPowerLab/ATX-Raspi";
+    mainProgram = "gpiosimtest";
+  };
+}
diff --git a/nix/pkgs/gpiosimtest/go.mod b/nix/pkgs/gpiosimtest/go.mod
new file mode 100644
index 0000000..b72aa88
--- /dev/null
+++ b/nix/pkgs/gpiosimtest/go.mod
@@ -0,0 +1,39 @@
+module github.com/LowPowerLab/ATX-Raspi/gpiosimtest
+
+go 1.21.4
+
+require (
+	github.com/gin-gonic/gin v1.10.0
+	github.com/warthog618/go-gpiosim v0.1.1
+)
+
+require (
+	github.com/bytedance/sonic v1.11.6 // indirect
+	github.com/bytedance/sonic/loader v0.1.1 // indirect
+	github.com/cloudwego/base64x v0.1.4 // indirect
+	github.com/cloudwego/iasm v0.2.0 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.3 // indirect
+	github.com/gin-contrib/sse v0.1.0 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/go-playground/validator/v10 v10.20.0 // indirect
+	github.com/goccy/go-json v0.10.2 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.7 // indirect
+	github.com/leodido/go-urn v1.4.0 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/pelletier/go-toml/v2 v2.2.2 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
+	github.com/ugorji/go/codec v1.2.12 // indirect
+	github.com/warthog618/go-gpiocdev v0.9.1 // indirect
+	golang.org/x/arch v0.8.0 // indirect
+	golang.org/x/crypto v0.23.0 // indirect
+	golang.org/x/net v0.25.0 // indirect
+	golang.org/x/sys v0.20.0 // indirect
+	golang.org/x/text v0.15.0 // indirect
+	google.golang.org/protobuf v1.34.1 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/nix/pkgs/gpiosimtest/go.sum b/nix/pkgs/gpiosimtest/go.sum
new file mode 100644
index 0000000..70a0f2c
--- /dev/null
+++ b/nix/pkgs/gpiosimtest/go.sum
@@ -0,0 +1,95 @@
+github.com/bytedance/sonic v1.11.6 h1:oUp34TzMlL+OY1OUWxHqsdkgC/Zfc85zGqw9siXjrc0=
+github.com/bytedance/sonic v1.11.6/go.mod h1:LysEHSvpvDySVdC2f87zGWf6CIKJcAvqab1ZaiQtds4=
+github.com/bytedance/sonic/loader v0.1.1 h1:c+e5Pt1k/cy5wMveRDyk2X4B9hF4g7an8N3zCYjJFNM=
+github.com/bytedance/sonic/loader v0.1.1/go.mod h1:ncP89zfokxS5LZrJxl5z0UJcsk4M4yY2JpfqGeCtNLU=
+github.com/cloudwego/base64x v0.1.4 h1:jwCgWpFanWmN8xoIUHa2rtzmkd5J2plF/dnLS6Xd/0Y=
+github.com/cloudwego/base64x v0.1.4/go.mod h1:0zlkT4Wn5C6NdauXdJRhSKRlJvmclQ1hhJgA0rcu/8w=
+github.com/cloudwego/iasm v0.2.0 h1:1KNIy1I1H9hNNFEEH3DVnI4UujN+1zjpuk6gwHLTssg=
+github.com/cloudwego/iasm v0.2.0/go.mod h1:8rXZaNYT2n95jn+zTI1sDr+IgcD2GVs0nlbbQPiEFhY=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gabriel-vasile/mimetype v1.4.3 h1:in2uUcidCuFcDKtdcBxlR0rJ1+fsokWf+uqxgUFjbI0=
+github.com/gabriel-vasile/mimetype v1.4.3/go.mod h1:d8uq/6HKRL6CGdk+aubisF/M5GcPfT7nKyLpA0lbSSk=
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+golang.org/x/text v0.15.0 h1:h1V/4gjBv8v9cjcR6+AR5+/cIYK5N/WAgiv4xlsEtAk=
+golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/protobuf v1.34.1 h1:9ddQBjfCyZPOHPUiPxpYESBLc+T8P3E+Vo4IbKZgFWg=
+google.golang.org/protobuf v1.34.1/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+nullprogram.com/x/optparse v1.0.0/go.mod h1:KdyPE+Igbe0jQUrVfMqDMeJQIJZEuyV7pjYmp6pbG50=
+rsc.io/pdf v0.1.1/go.mod h1:n8OzWcQ6Sp37PL01nO98y4iUCRdTGarVfzxY20ICaU4=
diff --git a/nix/pkgs/gpiosimtest/main.go b/nix/pkgs/gpiosimtest/main.go
new file mode 100644
index 0000000..4dc2270
--- /dev/null
+++ b/nix/pkgs/gpiosimtest/main.go
@@ -0,0 +1,201 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+	gpiosim "github.com/warthog618/go-gpiosim"
+)
+
+const (
+	ENOLINE = -1
+)
+
+func retrieveLineOffset(g *gpiosim.Simpleton, spec string) (int, error) {
+	offset, err := strconv.Atoi(spec)
+	if err != nil {
+		return ENOLINE, err
+	}
+
+	if offset < 0 || offset >= g.Config().NumLines {
+		return ENOLINE, fmt.Errorf("offset must be an integer between 0 and %d; got %d", g.Config().NumLines-1, offset)
+	}
+
+	return offset, nil
+}
+
+func handleLineOffset(c *gin.Context, g *gpiosim.Simpleton, spec string) (int, error) {
+	offset, err := retrieveLineOffset(g, spec)
+	if err != nil {
+		respondNotFound(c, err, gin.H{
+			"offset": offset,
+		})
+	}
+
+	return offset, err
+}
+
+func handleLevel(c *gin.Context, g *gpiosim.Simpleton, offset int) {
+	level, err := g.Level(offset)
+	if err != nil {
+		respondInternalServerError(c, err, gin.H{"offset": offset, "level": level})
+	} else {
+		respondOk(c, gin.H{"offset": offset, "level": level})
+	}
+}
+
+func handlePull(c *gin.Context, g *gpiosim.Simpleton, offset int) {
+	pull, err := g.Pull(offset)
+	if err != nil {
+		respondInternalServerError(c, err, gin.H{"offset": offset, "pull": pull})
+	} else {
+		respondOk(c, gin.H{"offset": offset, "pull": pull})
+	}
+}
+
+func respond(c *gin.Context, st int, err error, data gin.H) {
+	c.JSON(st, gin.H{"error": err, "data": data})
+}
+
+func respondOk(c *gin.Context, data gin.H) {
+	respond(c, http.StatusOK, nil, data)
+}
+
+func respondBadRequest(c *gin.Context, err error, data gin.H) {
+	respond(c, http.StatusBadRequest, err, data)
+}
+
+func respondNotFound(c *gin.Context, err error, data gin.H) {
+	respond(c, http.StatusNotFound, err, data)
+}
+
+func respondInternalServerError(c *gin.Context, err error, data gin.H) {
+	respond(c, http.StatusInternalServerError, err, data)
+}
+
+func main() {
+	lines, ok := os.LookupEnv("LINES")
+	var linei int
+	if ok {
+		linec, err := strconv.Atoi(lines)
+		if err != nil {
+			fmt.Printf("error parsing LINES specification %v: %v\n", lines, err)
+			os.Exit(1)
+		} else {
+			linei = linec
+		}
+	} else {
+		linei = 9
+	}
+
+	g, err := gpiosim.NewSimpleton(linei)
+	if err != nil {
+		fmt.Printf("error creating simulated GPIO: %v\n", err)
+		os.Exit(1)
+	}
+
+	defer g.Close()
+
+	r := gin.Default()
+
+	r.GET("/", func(c *gin.Context) {
+		respondOk(c, gin.H{
+			"chipname": g.ChipName(),
+			"config":   g.Config(),
+			"devpath":  g.DevPath(),
+		})
+	})
+
+	r.GET("/chipname", func(c *gin.Context) {
+		respondOk(c, gin.H{"chipname": g.ChipName()})
+	})
+
+	r.GET("/config", func(c *gin.Context) {
+		respondOk(c, gin.H{"config": g.Config()})
+	})
+
+	r.GET("/devpath", func(c *gin.Context) {
+		respondOk(c, gin.H{"devpath": g.DevPath()})
+	})
+
+	r.GET("/line/:offset/level", func(c *gin.Context) {
+		offset, err := handleLineOffset(c, g, c.Param("offset"))
+		if err != nil {
+			return
+		}
+
+		handleLevel(c, g, offset)
+	})
+
+	r.GET("/line/:offset/pull", func(c *gin.Context) {
+		offset, err := handleLineOffset(c, g, c.Param("offset"))
+		if err != nil {
+			return
+		}
+
+		handlePull(c, g, offset)
+	})
+
+	r.PUT("/line/:offset/pull/down", func(c *gin.Context) {
+		offset, err := handleLineOffset(c, g, c.Param("offset"))
+		if err != nil {
+			return
+		}
+
+		if err := g.Pulldown(offset); err != nil {
+			respondInternalServerError(c, err, gin.H{"offset": offset})
+		} else {
+			handlePull(c, g, offset)
+		}
+	})
+
+	r.PUT("/line/:offset/pull/up", func(c *gin.Context) {
+		offset, err := handleLineOffset(c, g, c.Param("offset"))
+		if err != nil {
+			return
+		}
+
+		if err := g.Pullup(offset); err != nil {
+			respondInternalServerError(c, err, gin.H{"offset": offset})
+		} else {
+			handlePull(c, g, offset)
+		}
+	})
+
+	r.PUT("/line/:offset/pull/:bias", func(c *gin.Context) {
+		offset, err := handleLineOffset(c, g, c.Param("offset"))
+		if err != nil {
+			return
+		}
+
+		bias, err := strconv.Atoi(c.Param("bias"))
+		if err != nil {
+			respondBadRequest(c, err, gin.H{"offset": offset, "bias": bias})
+			return
+		}
+
+		if err := g.SetPull(offset, bias); err != nil {
+			respondInternalServerError(c, err, gin.H{"offset": offset, "bias": bias})
+		} else {
+			handlePull(c, g, offset)
+		}
+	})
+
+	r.PUT("/line/:offset/pull/toggle", func(c *gin.Context) {
+		offset, err := handleLineOffset(c, g, c.Param("offset"))
+		if err != nil {
+			return
+		}
+
+		if err := g.Toggle(offset); err != nil {
+			respondInternalServerError(c, err, gin.H{"offset": offset})
+		} else {
+			handlePull(c, g, offset)
+		}
+	})
+
+	r.Run()
+}
diff --git a/shutdowncheck.sh b/shutdowncheck.sh
new file mode 100755
index 0000000..49a9304
--- /dev/null
+++ b/shutdowncheck.sh
@@ -0,0 +1,212 @@
+#!/bin/sh
+
+# ATXRaspi/MightyHat interrupt based shutdown/reboot script
+# Script by Felix Rusu
+
+set -eu
+
+header() {
+  if [ "$#" -lt 2 ]; then
+    echo 1>&2 'internal error: usage: header <padding> <line> [<line>...]'
+    return 64 # EX_USAGE
+  fi
+
+  padding="${1:-0}"
+  shift
+
+  if [ "$((padding+0))" != "$padding" ]; then
+    echo 1>&2 'internal error: padding must be an integer'
+    return 64 # EX_USAGE
+  fi
+
+  left=''
+  while [ "$padding" -gt 0 ]; do
+    left="${left} "
+    padding="$((padding-1))"
+  done
+
+  echo "=========================================================================================="
+  for line in "$@"; do
+    echo "${left}${line}"
+  done
+  echo "=========================================================================================="
+}
+
+f2nsec() {
+  case "${1?}" in
+    *.*.*)
+      echo 1>&2 "Not a valid decimal number: ${1}"
+      return 1
+      ;;
+    *.*)
+      __f2nsec_whole="${1%%.*}"
+      __f2nsec_fractional="${1#*.}"
+
+      __f2nsec_exp="${#__f2nsec_fractional}"
+      __f2nsec_scale=1
+
+      while [ "$__f2nsec_exp" -gt 0 ]; do
+        __f2nsec_scale="$(( __f2nsec_scale * 10 ))"
+        __f2nsec_exp="$(( __f2nsec_exp - 1 ))"
+      done
+
+      echo "$(( (__f2nsec_whole * 1000000000) + ((__f2nsec_fractional * 1000000000) / __f2nsec_scale) ))"
+      ;;
+    *)
+      echo "$(( "$1" * 1000000000 ))"
+      ;;
+  esac
+}
+
+ATX_RASPI_PULSE_MIN="${ATX_RASPI_PULSE_MIN:-0.2}"
+ATX_RASPI_PULSE_MAX="${ATX_RASPI_PULSE_MAX:-0.6}"
+
+REBOOTPULSEMINIMUM="$(f2nsec "$ATX_RASPI_PULSE_MIN")" #reboot pulse signal should be at least this long
+REBOOTPULSEMAXIMUM="$(f2nsec "$ATX_RASPI_PULSE_MAX")" #reboot pulse signal should be at most this long
+
+#This is GPIO 7 (pin 26 on the pinout diagram).
+#This is an input from ATXRaspi to the Pi.
+#When button is held for ~3 seconds, this pin will become HIGH signaling to this script to poweroff the Pi.
+SHUTDOWN="${ATX_RASPI_SHUTDOWN_PIN:-7}"
+
+#Added reboot feature (with ATXRaspi R2.6 (or ATXRaspi 2.5 with blue dot on chip)
+#Hold ATXRaspi button for at least 500ms but no more than 2000ms and a reboot HIGH pulse of 500ms length will be issued
+#This is GPIO 8 (pin 24 on the pinout diagram).
+#This is an output from Pi to ATXRaspi and signals that the Pi has booted.
+#This pin is asserted HIGH as soon as this script runs (by writing "1" to /sys/class/gpio/gpio8/value)
+BOOT="${ATX_RASPI_BOOT_PIN:-8}"
+
+CHIP="${ATX_RASPI_CHIP:-/dev/gpiochip0}"
+
+failed=''
+
+if [ "$REBOOTPULSEMINIMUM" -le 0 ]; then
+  failed="${failed:+"${failed}, "}ATX_RASPI_PULSE_MIN (${ATX_RASPI_PULSE_MIN}) must be greater than 0"
+fi
+
+if [ "$REBOOTPULSEMAXIMUM" -le "$REBOOTPULSEMINIMUM" ]; then
+  failed="${failed:+"${failed}, "}ATX_RASPI_PULSE_MAX (${ATX_RASPI_PULSE_MAX}) must be greater than ATX_RASPI_PULSE_MIN (${ATX_RASPI_PULSE_MIN})"
+fi
+
+if [ "$SHUTDOWN" -lt 0 ]; then
+  failed="${failed:+"${failed}, "}ATX_RASPI_SHUTDOWN_PIN (${SHUTDOWN}) must be greater than 0"
+fi
+
+if [ "$BOOT" -lt 0 ]; then
+  failed="${failed:+"${failed}, "}ATX_RASPI_BOOT_PIN (${BOOT}) must be greater than 0"
+fi
+
+if [ "$SHUTDOWN" -eq "$BOOT" ]; then
+  failed="${failed:+"${failed}, "}ATX_RASPI_SHUTDOWN_PIN (${SHUTDOWN}) must be distinct from ATX_RASPI_BOOT_PIN (${BOOT})"
+fi
+
+if [ -n "${failed:-}" ]; then
+  echo 1>&2 "ERROR: $failed"
+  exit 1
+fi
+
+if [ -n "${ATX_RASPI_DRY_RUN:-}" ]; then
+  handle_press() {
+    echo "[dry-run] $*"
+  }
+else
+  handle_press() {
+    "$@"
+  }
+fi
+
+if { command -v gpioset && command -v gpiomon ; } 1>/dev/null 2>&1; then
+  init_shutdown_pin() {
+    # NOP
+    :
+  }
+
+  init_boot_pin() {
+    gpioset -z -b pull-up -t 0 -c "${CHIP?}" "${BOOT?}=1"
+  }
+
+  watch_shutdown_pin() {
+    gpiomon -c "${CHIP?}" -F '%e %S' "${SHUTDOWN?}" | while read -r event seconds; do
+      case "$event" in
+        # Rising
+        1)
+          pulseStart="$(f2nsec "$seconds")"
+          ;;
+        # Falling
+        2)
+          pulseEnd="$(f2nsec "$seconds")"
+          pulseStart="${pulseStart:-"$pulseEnd"}"
+          pulseDuration="$(( pulseEnd - pulseStart ))"
+
+          if [ "$pulseDuration" -gt "$REBOOTPULSEMAXIMUM" ]; then
+            header 12 "SHUTDOWN request on chip ${CHIP?} from GPIO${SHUTDOWN}, halting Rpi ..."
+            handle_press poweroff
+            return
+          elif [ "$pulseDuration" -gt "$REBOOTPULSEMINIMUM" ]; then
+            header 12 "REBOOT request on chip ${CHIP?} from GPIO${SHUTDOWN?}, recycling Rpi ..."
+            handle_press reboot
+            return
+          else
+            unset pulseStart pulseEnd
+          fi
+          ;;
+        *)
+          echo 1>&2 "WARNING: unrecognized event '${event}' on chip ${CHIP?} for GPIO${SHUTDOWN?}; ignoring."
+          ;;
+      esac
+    done
+  }
+elif [ -e /sys/class/gpio/export ]; then
+  init_shutdown_pin() {
+    echo "${SHUTDOWN?}" > /sys/class/gpio/export
+    echo in > "/sys/class/gpio/gpio${SHUTDOWN?}/direction"
+  }
+
+  init_boot_pin() {
+    echo "${BOOT?}" > /sys/class/gpio/export
+    echo out > "/sys/class/gpio/gpio${BOOT?}/direction"
+    echo 1 > "/sys/class/gpio/gpio${BOOT?}/value"
+  }
+
+  watch_shutdown_pin() {
+    #This loop continuously checks if the shutdown button was pressed on
+    #ATXRaspi (GPIO7 to become HIGH), and issues a shutdown when that happens.
+    #It sleeps as long as that has not happened.
+    while true; do
+      shutdownSignal="$(cat "/sys/class/gpio/gpio${SHUTDOWN}/value")"
+      if [ "$shutdownSignal" = 0 ]; then
+        sleep 0.2
+      else
+        pulseStart="$(date +%s%N)" # mark the time when Shutoff signal went HIGH (milliseconds since epoch)
+        while [ "$shutdownSignal" = 1 ]; do
+          sleep 0.02
+          if [ "$(( "$(date +%s%N)" - pulseStart ))" -gt "$REBOOTPULSEMAXIMUM" ]; then
+            header 12 "SHUTDOWN request from GPIO${SHUTDOWN}, halting Rpi ..."
+            handle_press poweroff
+            return
+          fi
+          shutdownSignal="$(cat "/sys/class/gpio/gpio${SHUTDOWN}/value")"
+        done
+        #pulse went LOW, check if it was long enough, and trigger reboot
+        if [ "$(( "$(date +%s%N)" - pulseStart ))" -gt "$REBOOTPULSEMINIMUM" ]; then
+          header 12 "REBOOT request from GPIO${SHUTDOWN}, recycling Rpi ..."
+          handle_press reboot
+          return
+        fi
+      fi
+    done
+  }
+else
+  # shellcheck disable=SC2016
+  echo 1>&2 'FATAL: missing `libgpiod` tools (`gpioset`, `gpiomon`), and legacy sysfs GPIO interface is unavailable; terminating.'
+  exit 1
+fi
+
+init_shutdown_pin
+init_boot_pin
+
+header 3 \
+   "ATXRaspi shutdown POLLING script started: asserted pins ($SHUTDOWN=input,LOW; $BOOT=output,HIGH)" \
+   "Waiting for GPIO$SHUTDOWN to become HIGH (short HIGH pulse=REBOOT, long pulse HIGH=SHUTDOWN)..."
+
+watch_shutdown_pin
diff --git a/shutdowncheckOpenElec.sh b/shutdowncheckOpenElec.sh
new file mode 120000
index 0000000..cfe9e86
--- /dev/null
+++ b/shutdowncheckOpenElec.sh
@@ -0,0 +1 @@
+shutdowncheck.sh
\ No newline at end of file
diff --git a/shutdownchecksetup.sh b/shutdownchecksetup.sh
index 67dd567..d5d9994 100644
--- a/shutdownchecksetup.sh
+++ b/shutdownchecksetup.sh
@@ -1,130 +1,168 @@
-#!/bin/bash
-
-OPTION=$(whiptail --title "ATXRaspi/MightyHat shutdown/reboot script setup" --menu "\nChoose your script type option below:\n\n(Note: changes require reboot to take effect)" 15 78 4 \
-"1" "Install INTERRUPT based script /etc/shutdownirq.py (recommended)" \
-"2" "Install POLLING based script /etc/shutdowncheck.sh (classic)" \
-"3" "Disable any existing shutdown script" 3>&1 1>&2 2>&3)
- 
-exitstatus=$?
-if [ $exitstatus = 0 ]; then
-    sudo sed -e '/shutdown/ s/^#*/#/' -i /etc/rc.local
-
-    if [ $OPTION = 1 ]; then
-      echo '#!/usr/bin/python
-# ATXRaspi/MightyHat interrupt based shutdown/reboot script
-# Script by Tony Pottier, Felix Rusu
-import RPi.GPIO as GPIO
-import os
-import sys
-import time
-
-GPIO.setmode(GPIO.BCM) 
-
-pulseStart = 0.0
-REBOOTPULSEMINIMUM = 0.2	#reboot pulse signal should be at least this long (seconds)
-REBOOTPULSEMAXIMUM = 1.0	#reboot pulse signal should be at most this long (seconds)
-SHUTDOWN = 7							#GPIO used for shutdown signal
-BOOT = 8								#GPIO used for boot signal
-
-# Set up GPIO 8 and write that the PI has booted up
-GPIO.setup(BOOT, GPIO.OUT, initial=GPIO.HIGH)
-
-# Set up GPIO 7  as interrupt for the shutdown signal to go HIGH
-GPIO.setup(SHUTDOWN, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
-
-print("\n==========================================================================================")
-print("   ATXRaspi shutdown IRQ script started: asserted pins (",SHUTDOWN, "=input,LOW; ",BOOT,"=output,HIGH)")
-print("   Waiting for GPIO", SHUTDOWN, "to become HIGH (short HIGH pulse=REBOOT, long HIGH=SHUTDOWN)...")
-print("==========================================================================================")
-try:
-	while True:	
-		GPIO.wait_for_edge(SHUTDOWN, GPIO.RISING)
-		shutdownSignal = GPIO.input(SHUTDOWN)
-		pulseStart = time.time() #register time at which the button was pressed
-		while shutdownSignal:
-			time.sleep(0.2)
-			if(time.time() - pulseStart >= REBOOTPULSEMAXIMUM):
-				print("\n=====================================================================================")
-				print("            SHUTDOWN request from GPIO", SHUTDOWN, ", halting Rpi ...")
-				print("=====================================================================================")
-				os.system("sudo poweroff")
-				sys.exit()
-			shutdownSignal = GPIO.input(SHUTDOWN)
-		if time.time() - pulseStart >= REBOOTPULSEMINIMUM:
-			print("\n=====================================================================================")
-			print("            REBOOT request from GPIO", SHUTDOWN, ", recycling Rpi ...")
-			print("=====================================================================================")
-			os.system("sudo reboot")
-			sys.exit()
-		if GPIO.input(SHUTDOWN): #before looping we must make sure the shutdown signal went low
-			GPIO.wait_for_edge(SHUTDOWN, GPIO.FALLING)
-except:
-	pass 
-finally:
-	GPIO.cleanup()' > /etc/shutdownirq.py
-      sudo sed -i '$ i python /etc/shutdownirq.py &' /etc/rc.local
-    elif [ $OPTION = 2 ]; then
-      echo '#!/bin/bash
-# ATXRaspi/MightyHat interrupt based shutdown/reboot script
-# Script by Felix Rusu
-
-#This is GPIO 7 (pin 26 on the pinout diagram).
-#This is an input from ATXRaspi to the Pi.
-#When button is held for ~3 seconds, this pin will become HIGH signalling to this script to poweroff the Pi.
-SHUTDOWN=7
-REBOOTPULSEMINIMUM=200      #reboot pulse signal should be at least this long
-REBOOTPULSEMAXIMUM=600      #reboot pulse signal should be at most this long
-echo "$SHUTDOWN" > /sys/class/gpio/export
-echo "in" > /sys/class/gpio/gpio$SHUTDOWN/direction
-#Added reboot feature (with ATXRaspi R2.6 (or ATXRaspi 2.5 with blue dot on chip)
-#Hold ATXRaspi button for at least 500ms but no more than 2000ms and a reboot HIGH pulse of 500ms length will be issued
-#This is GPIO 8 (pin 24 on the pinout diagram).
-#This is an output from Pi to ATXRaspi and signals that the Pi has booted.
-#This pin is asserted HIGH as soon as this script runs (by writing "1" to /sys/class/gpio/gpio8/value)
-BOOT=8
-echo "$BOOT" > /sys/class/gpio/export
-echo "out" > /sys/class/gpio/gpio$BOOT/direction
-echo "1" > /sys/class/gpio/gpio$BOOT/value
-
-echo -e "\n=========================================================================================="
-echo "   ATXRaspi shutdown POLLING script started: asserted pins ($SHUTDOWN=input,LOW; $BOOT=output,HIGH)"
-echo "   Waiting for GPIO$SHUTDOWN to become HIGH (short HIGH pulse=REBOOT, long HIGH=SHUTDOWN)..."
-echo "=========================================================================================="
-
-#This loop continuously checks if the shutdown button was pressed on ATXRaspi (GPIO7 to become HIGH), and issues a shutdown when that happens.
-#It sleeps as long as that has not happened.
-while [ 1 ]; do
-  shutdownSignal=$(cat /sys/class/gpio/gpio$SHUTDOWN/value)
-  if [ $shutdownSignal = 0 ]; then
-    /bin/sleep 0.2
-  else  
-    pulseStart=$(date +%s%N | cut -b1-13) # mark the time when Shutoff signal went HIGH (milliseconds since epoch)
-    while [ $shutdownSignal = 1 ]; do
-      /bin/sleep 0.02
-      if [ $(($(date +%s%N | cut -b1-13)-$pulseStart)) -gt $REBOOTPULSEMAXIMUM ]; then
-        echo -e "\n====================================================================================="
-        echo "            SHUTDOWN request from GPIO", SHUTDOWN, ", halting Rpi ..."
-        echo "====================================================================================="
-        sudo poweroff
-        exit
-      fi
-      shutdownSignal=$(cat /sys/class/gpio/gpio$SHUTDOWN/value)
-    done
-    #pulse went LOW, check if it was long enough, and trigger reboot
-    if [ $(($(date +%s%N | cut -b1-13)-$pulseStart)) -gt $REBOOTPULSEMINIMUM ]; then 
-      echo -e "\n====================================================================================="
-      echo "            REBOOT request from GPIO", SHUTDOWN, ", recycling Rpi ..."
-      echo "====================================================================================="
-      sudo reboot
-      exit
+#!/bin/sh
+
+set -eu
+
+SHUTDOWNCHECK_OWNER="${SHUTDOWNCHECK_OWNER:-LowPowerLab}"
+SHUTDOWNCHECK_REPO="${SHUTDOWNCHECK_REPO:-ATX-Raspi}"
+SHUTDOWNCHECK_REV="${SHUTDOWNCHECK_REV:-master}"
+SHUTDOWNCHECK_BASEURL="${SHUTDOWNCHECK_BASEURL:-"https://raw.githubusercontent.com/${SHUTDOWNCHECK_OWNER}/${SHUTDOWNCHECK_REPO}/${SHUTDOWNCHECK_REV}"}"
+
+# We provide a fallback in case `EUID` is not set; silence shellcheck violation
+# warning that "In POSIX sh, EUID is undefined"
+# shellcheck disable=SC3028
+if [ "${EUID:-$(id -u 2> /dev/null || :)}" != 0 ]; then
+    run_as_root() {
+        sudo "$@"
+    }
+else
+    run_as_root() {
+        "$@"
+    }
+fi
+
+if command -v curl 1> /dev/null 2>&1; then
+    fetch() {
+        run_as_root curl -fsSLo "$2" "$1"
+    }
+elif command -v wget 1> /dev/null 2>&1; then
+    fetch() {
+        run_as_root wget -o "$2" "$1"
+    }
+else
+    fetch() {
+        echo 1>&2 "neither curl nor wget are available; cannot fetch '$1' into '$2'"
+        return 127
+    }
+fi
+
+install_interrupt_script() {
+    dest="${1:-/etc/shutdownirq.py}"
+    fetch "${SHUTDOWNCHECK_BASEURL}/shutdownirq.py" "$dest"
+    run_as_root chmod +x "$dest"
+    if [ -f /etc/rc.local ]; then
+        run_as_root sed -i "$ i python ${dest} &" /etc/rc.local
     fi
-  fi
-done' > /etc/shutdowncheck.sh
-sudo chmod +x /etc/shutdowncheck.sh
-sudo sed -i '$ i /etc/shutdowncheck.sh &' /etc/rc.local
+}
+
+install_polling_script() {
+    dest="${1:-/etc/shutdowncheck.sh}"
+    fetch "${SHUTDOWNCHECK_BASEURL}/shutdowncheck.sh" "$dest"
+    run_as_root chmod +x "$dest"
+    if [ -f /etc/rc.local ]; then
+        run_as_root sed -i "\$ i ${dest} &" /etc/rc.local
     fi
-    
-    echo "You chose option" $OPTION ": All done!"
+}
+
+looks_like_elec_distro() {
+    # shellcheck disable=SC1091
+    . /etc/os-release 1> /dev/null 2>&1 || :
+
+    case "${NAME:-}" in
+        *ELEC)
+            return 0
+            ;;
+    esac
+
+    case "${ID:-}" in
+        *elec)
+            return 0
+            ;;
+    esac
+
+    # shellcheck disable=SC3028
+    # *ELEC distros:
+    #   1. Use `root` for shell sessions,
+    #   2. Have the directory `/storage/.config`, and
+    #   3. Use a `sudo` wrapper that issues a warning about not needing sudo
+    #      and then exits with a non-zero status.
+    [ "${EUID:-$(id -u 2> /dev/null || :)}" -eq 0 ] && [ -d /storage/.config ] && ! sudo true
+}
+
+if looks_like_elec_distro; then
+    dest="${SHUTDOWNCHECK_POLLING_DEST:-${SHUTDOWNCHECK_DEST:-/storage/.config/shutdowncheck.sh}}"
+    install_polling_script "$dest"
+    run_as_root "${SHELL:-/bin/sh}" "-$-" -c "
+echo '#!/bin/sh
+(
+${dest}
+)&' > /storage/.config/autostart.sh
+"
+    chmod 777 /storage/.config/autostart.sh
+    chmod 777 "$dest"
+    exit
+fi
+
+if command -v whiptail 1> /dev/null 2>&1; then
+    get_script_type() {
+        whiptail --title "ATXRaspi/MightyHat shutdown/reboot script setup" --menu "\nChoose your script type option below:\n\n(Note: changes require reboot to take effect)" 15 78 4 \
+            "1" "Install INTERRUPT based script /etc/shutdownirq.py (recommended)" \
+            "2" "Install POLLING based script /etc/shutdowncheck.sh (classic)" \
+            "3" "Disable any existing shutdown script" 3>&1 1>&2 2>&3
+    }
+elif (help select) 1> /dev/null 2>&1; then
+    # Eval this, as otherwise we're liable to get a syntax error from shells that
+    # do not understand `select ...; do ...; done`
+    eval '
+        get_script_type() {
+            echo 1>&2 "ATXRaspi/MightyHat shutdown/reboot script setup"
+            echo 1>&2 "Choose your script type option below (note: changes require reboot to take effect)"
+
+            # shellcheck disable=SC3043
+            local PS3="Choose your script type option: "
+
+            # shellcheck disable=SC3008
+            select CHOICE in "Install INTERRUPT based script /etc/shutdownirq.py (recommended)" \
+                "Install POLLING based script /etc/shutdowncheck.sh (classic)" \
+                "Disable any existing shutdown script"; do
+                if [ -n "${CHOICE:-}" ]; then
+                    echo "$REPLY"
+                    break
+                else
+                    echo 1>&2 "Not a valid choice: ${REPLY}"
+                fi
+            done
+        }
+    '
+else
+    get_script_type() {
+        echo 1>&2 'ATXRaspi/MightyHat shutdown/reboot script setup'
+        echo 1>&2 "Choose your script type option below (note: changes require reboot to take effect)"
+        echo 1>&2 "\
+1) Install INTERRUPT based script /etc/shutdownirq.py (recommended)
+2) Install POLLING based script /etc/shutdowncheck.sh (classic)
+3) Disable any existing shutdown script"
+
+        while true; do
+            echo 1>&2 'Choose your script type option: '
+
+            if read -r REPLY; then
+                case "${REPLY:-}" in
+                    1 | 2 | 3)
+                        echo "$REPLY"
+                        return
+                        ;;
+                    *)
+                        echo 1>&2 "Not a valid choice: ${REPLY}"
+                        ;;
+                esac
+            fi
+        done
+    }
+fi
+
+if OPTION="$(get_script_type)"; then
+    run_as_root sed -e '/shutdown/ s/^#*/#/' -i /etc/rc.local
+
+    case "$OPTION" in
+        1)
+            install_interrupt_script "${SHUTDOWNCHECK_INTERRUPT_DEST:-${SHUTDOWNCHECK_DEST:-}}"
+            ;;
+        2)
+            install_polling_script "${SHUTDOWNCHECK_POLLING_DEST:-${SHUTDOWNCHECK_DEST:-}}"
+            ;;
+    esac
+
+    echo "You chose option ${OPTION}: All done!"
 else
     echo "Shutdown/Reboot script setup was aborted."
 fi
diff --git a/shutdownchecksetupOpenElec.sh b/shutdownchecksetupOpenElec.sh
deleted file mode 100644
index ff8c728..0000000
--- a/shutdownchecksetupOpenElec.sh
+++ /dev/null
@@ -1,56 +0,0 @@
-#!/bin/sh
-echo '#!/bin/bash
-
-#This is GPIO 7 (pin 26 on the pinout diagram).
-#This is an input from ATXRaspi to the Pi.
-#When button is held for ~3 seconds, this pin will become HIGH signalling to this script to poweroff the Pi.
-SHUTDOWN=7
-REBOOTPULSEMINIMUM=200      #reboot pulse signal should be at least this long
-REBOOTPULSEMAXIMUM=600      #reboot pulse signal should be at most this long
-echo "$SHUTDOWN" > /sys/class/gpio/export
-echo "in" > /sys/class/gpio/gpio$SHUTDOWN/direction
-
-#Added reboot feature (with ATXRaspi R2.6 (or ATXRaspi 2.5 with blue dot on chip)
-#Hold ATXRaspi button for at least 500ms but no more than 2000ms and a reboot HIGH pulse of 500ms length will be issued
-
-#This is GPIO 8 (pin 24 on the pinout diagram).
-#This is an output from Pi to ATXRaspi and signals that the Pi has booted.
-#This pin is asserted HIGH as soon as this script runs (by writing "1" to /sys/class/gpio/gpio8/value)
-BOOT=8
-echo "$BOOT" > /sys/class/gpio/export
-echo "out" > /sys/class/gpio/gpio$BOOT/direction
-echo "1" > /sys/class/gpio/gpio$BOOT/value
-
-echo "ATXRaspi shutdown script started: asserted pins ($SHUTDOWN=input,LOW; $BOOT=output,HIGH). Waiting for GPIO$SHUTDOWN to become HIGH..."
-
-#This loop continuously checks if the shutdown button was pressed on ATXRaspi (GPIO7 to become HIGH), and issues a shutdown when that happens.
-#It sleeps as long as that has not happened.
-while [ 1 ]; do
-  shutdownSignal=$(cat /sys/class/gpio/gpio$SHUTDOWN/value)
-  if [ $shutdownSignal = 0 ]; then
-    /bin/sleep 0.2
-  else  
-    pulseStart=$(date +%s%N | cut -b1-13) # mark the time when Shutoff signal went HIGH (milliseconds since epoch)
-    while [ $shutdownSignal = 1 ]; do
-      /bin/sleep 0.02
-      if [ $(($(date +%s%N | cut -b1-13)-$pulseStart)) -gt $REBOOTPULSEMAXIMUM ]; then
-        echo "ATXRaspi triggered a shutdown signal, halting Rpi ... "
-        poweroff
-        exit
-      fi
-      shutdownSignal=$(cat /sys/class/gpio/gpio$SHUTDOWN/value)
-    done
-    #pulse went LOW, check if it was long enough, and trigger reboot
-    if [ $(($(date +%s%N | cut -b1-13)-$pulseStart)) -gt $REBOOTPULSEMINIMUM ]; then 
-      echo "ATXRaspi triggered a reboot signal, recycling Rpi ... "
-      reboot
-      exit
-    fi
-  fi
-done' > /storage/.config/shutdowncheck.sh
-echo '#!/bin/bash
-(
-/storage/.config/shutdowncheck.sh
-)&' > /storage/.config/autostart.sh
-chmod 777 /storage/.config/autostart.sh
-chmod 777 /storage/.config/shutdowncheck.sh
\ No newline at end of file
diff --git a/shutdownchecksetupOpenElec.sh b/shutdownchecksetupOpenElec.sh
new file mode 120000
index 0000000..27c0bc0
--- /dev/null
+++ b/shutdownchecksetupOpenElec.sh
@@ -0,0 +1 @@
+shutdownchecksetup.sh
\ No newline at end of file
diff --git a/shutdownirq.py b/shutdownirq.py
new file mode 100755
index 0000000..db863b6
--- /dev/null
+++ b/shutdownirq.py
@@ -0,0 +1,150 @@
+#!/usr/bin/env python
+
+# ATXRaspi/MightyHat interrupt based shutdown/reboot script
+# Script by Tony Pottier, Felix Rusu
+
+import os
+import sys
+import time
+
+# Reboot pulse signal should be at least this long (seconds).
+REBOOTPULSEMINIMUM = float(os.environ.get("ATX_RASPI_PULSE_MIN", 0.2))
+
+# Reboot pulse signal should be at most this long (seconds).
+REBOOTPULSEMAXIMUM = float(os.environ.get("ATX_RASPI_PULSE_MAX", 1.0))
+
+# GPIO pin used for shutdown signal.
+SHUTDOWN = int(os.environ.get("ATX_RASPI_SHUTDOWN_PIN", 7))
+
+# GPIO pin used for boot signal.
+BOOT = int(os.environ.get("ATX_RASPI_BOOT_PIN", 8))
+
+failed = [msg for (cond, msg) in [
+    (REBOOTPULSEMINIMUM > 0, "ATX_RASPI_PULSE_MIN ({0}) must be greater than 0".format(REBOOTPULSEMINIMUM)),
+    (REBOOTPULSEMAXIMUM > REBOOTPULSEMINIMUM, "ATX_RASPI_PULSE_MAX ({0} must be greater than ATX_RASPI_PULSE_MIN ({1})".format(REBOOTPULSEMAXIMUM, REBOOTPULSEMINIMUM)),
+    (SHUTDOWN >= 0, "ATX_RASPI_SHUTDOWN_PIN ({0}) must be greater than 0".format(SHUTDOWN)),
+    (BOOT >= 0, "ATX_RASPI_BOOT_PIN ({0}) must be greater than 0".format(BOOT)),
+    (SHUTDOWN != 0, "ATX_RASPI_SHUTDOWN_PIN ({0}) must be distinct from ATX_RASPI_BOOT_PIN ({1})".format(SHUTDOWN, BOOT)),
+] if not cond]
+
+if len(failed) > 0:
+    raise ValueError(", ".join(failed))
+
+if os.environ.get("ATX_RASPI_DRY_RUN", "") == "":
+	def handle_press(*command):
+		os.system(*command)
+		sys.exit()
+else:
+	def handle_press(*command):
+		print("[dry-run] ", " ".join(command))
+		sys.exit()
+
+if os.environ.get("ATX_RASPI_DRY_RUN", "") == "":
+	def handle_press(*command):
+		os.system(*command)
+		sys.exit()
+else:
+	def handle_press(*command):
+		print("[dry-run] ", " ".join(command))
+		sys.exit()
+
+def diag(*msgs):
+	linelen = max([len(msg) for msg in msgs]) + 2
+	wrapper = "=" * linelen
+	print(wrapper)
+	for msg in msgs:
+		print(" {0}".format(msg))
+	print(wrapper)
+
+def announce():
+	print()
+	diag(
+		"ATXRaspi shutdown IRQ script started: asserted pins ({0}=input,LOW; {1}=output,HIGH)".format(SHUTDOWN, BOOT),
+		"Waiting for GPIO {0} to become HIGH (short HIGH pulse=REBOOT, long HIGH pulse=SHUTDOWN)...".format(SHUTDOWN),
+	)
+
+try:
+	import gpiod
+	from gpiod.line import Direction, Edge, Value
+	have_gpiod = True
+except ImportError:
+	have_gpiod = False
+
+if have_gpiod:
+
+	CHIP = os.environ.get("ATX_RASPI_CHIP", "/dev/gpiochip0")
+	CONSUMER = "atx-raspi"
+	CONFIG = {
+		SHUTDOWN: gpiod.LineSettings(direction=Direction.INPUT, edge_detection=Edge.BOTH),
+		BOOT: gpiod.LineSettings(direction=Direction.OUTPUT, output_value=Value.ACTIVE)
+	}
+
+	pulse_start = None
+
+	with gpiod.request_lines(CHIP, consumer=CONSUMER, config=CONFIG) as request:
+
+		announce()
+
+		try:
+			while True:
+				for event in request.read_edge_events():
+					if event.event_type is event.Type.RISING_EDGE:
+						pulse_start = time.time()
+					elif event.event_type is event.Type.FALLING_EDGE:
+						pulse_end = time.time()
+
+						if pulse_start is None:
+							pulse_start = pulse_end
+
+						pulse_duration = pulse_end - pulse_start
+
+						if pulse_duration >= REBOOTPULSEMAXIMUM:
+							print()
+							diag("SHUTDOWN request on chip {0} from GPIO{1}, halting Rpi ...".format(CHIP, SHUTDOWN))
+							handle_press("poweroff")
+							sys.exit()
+						elif pulse_duration >= REBOOTPULSEMINIMUM:
+							print()
+							diag("REBOOT request on chip {0} from GPIO{1}, recycling Rpi ...".format(CHIP, SHUTDOWN))
+							handle_press("reboot")
+							sys.exit()
+						else:
+							pulse_start = None
+							pulse_end = None
+		except Exception:
+			pass
+else:
+	import RPi.GPIO as GPIO
+
+	# Set up GPIO 8 and write that the PI has booted up
+	GPIO.setup(BOOT, GPIO.OUT, initial=GPIO.HIGH)
+
+	# Set up GPIO 7  as interrupt for the shutdown signal to go HIGH
+	GPIO.setup(SHUTDOWN, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
+
+	announce()
+
+	try:
+		while True:
+			GPIO.wait_for_edge(SHUTDOWN, GPIO.RISING)
+			shutdown_signal = GPIO.input(SHUTDOWN)
+			pulse_start = time.time() # register time at which the button was pressed
+			while shutdown_signal:
+				time.sleep(0.2)
+				if(time.time() - pulse_start >= REBOOTPULSEMAXIMUM):
+					print()
+					diag("SHUTDOWN request from GPIO{0}, halting Rpi ...".format(SHUTDOWN))
+					handle_press("poweroff")
+					sys.exit()
+				shutdown_signal = GPIO.input(SHUTDOWN)
+			if time.time() - pulse_start >= REBOOTPULSEMINIMUM:
+				print()
+				diag("REBOOT request from GPIO{0}, recycling Rpi ...".format(SHUTDOWN))
+				handle_press("reboot")
+				sys.exit()
+			if GPIO.input(SHUTDOWN): # before looping we must make sure the shutdown signal went low
+				GPIO.wait_for_edge(SHUTDOWN, GPIO.FALLING)
+	except Exception:
+		pass
+	finally:
+		GPIO.cleanup()