Installation for nixos based raspberry pi

[joehealy]

Extracted the polling version in a form suitable for nixos (could use the recommended version once RPi.GPIO has support for aarch64):

Save the following as /etc/nixos/shutdown-button.nix, then add it as an import into /etc/nixos/configuration.nix (ie add ./shutdown-button.nix as a line in the imports list) and run nixos-rebuild switch.

{pkgs, config, ... }:
  
let 

  shutdownCheck = pkgs.writeShellScriptBin "shutdownCheck" ''

# 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=465
REBOOTPULS {pkgs, config, ... }:
  
let 

  shutdownCheck = pkgs.writeShellScriptBin "shutdownCheck" ''

# 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=465
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=466
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
    ${pkgs.coreutils}/bin/sleep 0.2
  else  
    pulseStart=$(date +%s%N | cut -b1-13) # mark the time when Shutoff signal went HIGH (milliseconds since epoch)
    while [ $shutdownSignal = 1 ]; do
      ${pkgs.coreutils}/bin/sleep 0.02
      if [ $(($(date +%s%N | cut -b1-13)-$pulseStart)) -gt $REBOOTPULSEMAXIMUM ]; then
        echo -e "\n====================================================================================="
        echo "            SHUTDOWN request from GPIO", SHUTDOWN, ", halting Rpi ..."
        echo "====================================================================================="
        poweroff
        exit
      fi
      shutdownSignal=$(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 "====================================================================================="
      reboot
      exit
    fi
  fi
done

'';



in {


  systemd.services.shutdown-button = {
    description = "Shutdown Button";

    after = [ "multi-user.target" ];
    wantedBy = [ "multi-user.target" ];

    serviceConfig = {
      User = "root";
      ExecStart = "${shutdownCheck}/bin/shutdownCheck";
      Restart = "always";
    };
  };


}