Add integrations with Nix and NixOS

.actrc

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+-P ubuntu-latest=catthehacker/ubuntu:runner-latest

.editorconfig

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+# 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

.github/workflows/test.yml

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+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

.gitignore

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+# 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

doc/nixos-modules.md

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+## 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)
+
+