Initialize the SATA HAT on startup

configuration.nix

@@ -9,6 +9,8 @@
     "console=TTYAMA0,115200"
     "console=tty1"
     "8250.nr_uarts=1"
+    "iomem=relaxed"
+    "strict-devmem=0"
   ];
   boot.loader.raspberryPi = {
     enable = true;

modules/periodic.nix

@@ -28,7 +28,22 @@ in {
     startAt = "02:00:00";
   };
 
-    wantedBy = [ "default.target" ];
+  # Enable SATA HAT
+  systemd.services.sata-hat = {
+    description = "Enable software support for SATA Hat";
+    wantedBy = [ "zfs-import.target" ];
+    script = ''
+      ${pkgs.bash}/bin/bash -c "/etc/nixos/scripts/SATA-hat.sh on"
+    '';
+    serviceConfig = {
+      Type = "oneshot";
+      RemainAfterExit = "yes";
+      ExecStop = ''
+        ${pkgs.bash}/bin/bash -c "/etc/nixos/scripts/SATA-hat.sh off"
+      '';
     };
+    before = [ "zfs-import.target" "zfs-import-vault.service" ];
+    requires = [ "systemd-udev-settle.service" ];
+    after = [ "systemd-udev-settle.service" ];
   };
 }

scripts/SATA-hat.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+
+BASE_PATH=/sys/class/gpio
+
+# GPIO pins
+SATA0=26
+SATA1=25
+CPU_FAN=12
+
+# Values
+LOW=0
+HIGH=1
+
+export_pin() {
+	if [ ! -e $BASE_PATH/gpio"$1" ]; then
+		echo "$1" >$BASE_PATH/export
+	fi
+}
+
+unexport_pin() {
+	if [ -e $BASE_PATH/gpio"$1" ]; then
+		echo "$1" >$BASE_PATH/unexport
+	fi
+}
+
+set_mode() {
+	export_pin "$1"
+	echo "out" >$BASE_PATH/gpio"$1"/direction
+	echo "$2" >$BASE_PATH/gpio"$1"/value
+	if [ "$3" = "clean" ]; then
+		unexport_pin "$1"
+	fi
+}
+
+turn_on() {
+	set_mode $SATA0 $HIGH
+	sleep 1
+	set_mode $SATA1 $HIGH
+	set_mode $CPU_FAN $LOW
+}
+
+turn_off() {
+	set_mode $SATA0 $LOW clean
+	set_mode $SATA1 $LOW clean
+	set_mode $CPU_FAN $LOW clean
+}
+
+trap turn_off INT
+
+if [ "$1" = "on" ]; then
+	turn_on
+else
+	turn_off
+fi
+
+exit 0