NixOS on ARM/Raspberry Pi 4: Difference between revisions

NixOS on ARM/Raspberry Pi 4 (view source)

Revision as of 13:34, 22 October 2021

1,762 bytes added , 22 October 2021

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    '';
 </nowiki>}}
+==== Gpio and 1-wire ====
+{{file|/etc/nixos/configuration.nix|nix|<nowiki>
+  # add gpio group
+  users.groups.gpio = {};
+  # udev rule for gpio
+  services.udev.extraRules = ''
+    SUBSYSTEM=="bcm2835-gpiomem", KERNEL=="gpiomem", GROUP="gpio",MODE="0660"
+    SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", RUN+="${pkgs.bash}/bin/bash -c 'chown root:gpio  /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'"
+    SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add",RUN+="${pkgs.bash}/bin/bash -c 'chown root:gpio /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"
+  '';
+  # add user with gpio group
+  users = {
+    mutableUsers = false;
+    users.mygpiouser = {
+      isNormalUser = true;
+      password = "mygpiouserpasswd";
+      extraGroups = [ "wheel" "gpio" ];
+    };
+  };
+ # insert device tree snippet for 1-wire
+  hardware.deviceTree = {
+   enable = true;
+   overlays = [
+      {
+        name = "w1-gpio-overlay";
+        dtsText = ''
+	/dts-v1/;
+	/plugin/;
+	/ {
+	compatible = "brcm,bcm2711";
+	fragment@0 {
+		target-path = "/";
+		__overlay__ {
+			w1: onewire@0 {
+				compatible = "w1-gpio";
+				pinctrl-names = "default";
+				pinctrl-0 = <&w1_pins>;
+				gpios = <&gpio 4 0>;
+				rpi,parasitic-power = <0>;
+				status = "okay";
+			};
+		};
+	};
+	fragment@1 {
+		target = <&gpio>;
+		__overlay__ {
+			w1_pins: w1_pins {
+				brcm,pins = <4>;
+				brcm,function = <0>; // in (initially)
+				brcm,pull = <0>; // off
+			};
+		};
+	};
+	__overrides__ {
+		gpiopin =       <&w1>,"4",
+				<&w1_pins>,"brcm,pins:0";
+		pullup =        <&w1>,"rpi,parasitic-power:0";
+		};
+	};
+        '';
+      }
+    ];
+  };
+</nowiki>}}
 == Troubleshooting ==