diff --git a/cm4/default.nix b/cm4/default.nix
new file mode 100644
index 0000000..d77fff3
--- /dev/null
+++ b/cm4/default.nix
@@ -0,0 +1,37 @@
+{
+  config,
+  lib,
+  fn,
+  nixos-hardware,
+  ...
+}: let
+  inherit (lib) mkIf mkEnableOption mkOption types;
+  cfg = config.hardware.cm4;
+in {
+  options.hardware.cm4 = {
+    enable = mkEnableOption "custom CM4";
+  };
+
+  imports = [nixos-hardware.nixosModules.raspberry-pi-4] ++ (fn.scanPaths ./.);
+
+  config = mkIf cfg.enable {
+    hardware.raspberry-pi."4" = {
+      apply-overlays-dtmerge.enable = true;
+      xhci.enable = true;
+      overlays = {
+        audremap.enable = true;
+        spi-gpio40-45.enable = true;
+      };
+    };
+
+    hardware.deviceTree = {
+      enable = true;
+      filter = "*-rpi-cm4.dtb";
+    };
+
+    users.groups.spi = {};
+    services.udev.extraRules = ''
+      SUBSYSTEM=="spidev", KERNEL=="spidev0.0", GROUP="spi", MODE="0660"
+    '';
+  };
+}
diff --git a/cm4/dtb-audremap.nix b/cm4/dtb-audremap.nix
new file mode 100644
index 0000000..641a7cd
--- /dev/null
+++ b/cm4/dtb-audremap.nix
@@ -0,0 +1,51 @@
+{
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib) mkEnableOption mkIf mkMerge;
+  cfg = config.hardware.raspberry-pi."4".overlays;
+in {
+  options.hardware = {
+    raspberry-pi."4".overlays.audremap.enable = mkEnableOption ''audremap enable '';
+  };
+
+  config = mkMerge [
+    (mkIf cfg.audremap.enable {
+      hardware.deviceTree.overlays = [
+        {
+          name = "audremap.overlay";
+          filter = "*rpi-cm4*";
+          dtsText = ''
+            /dts-v1/;
+            /plugin/;
+            / {
+              compatible = "brcm,bcm2711";
+              fragment@0 {
+                target = <&audio_pins>;
+                frag0: __overlay__ {
+                  brcm,pins = <12 13>;
+                  brcm,function = <4>; /* alt0 alt0 */
+                };
+              };
+              fragment@1 {
+                target = <&chosen>;
+                __overlay__  {
+                  bootargs = "snd_bcm2835.enable_headphones=1";
+                };
+              };
+              __overrides__ {
+                swap_lr = <&frag0>, "swap_lr?";
+                enable_jack = <&frag0>, "enable_jack?";
+                pins_12_13 = <&frag0>,"brcm,pins:0=12", <&frag0>,"brcm,pins:4=13", <&frag0>,"brcm,function:0=4";
+                pins_18_19 = <&frag0>,"brcm,pins:0=18", <&frag0>,"brcm,pins:4=19", <&frag0>,"brcm,function:0=2";
+                pins_40_41 = <&frag0>,"brcm,pins:0=40", <&frag0>,"brcm,pins:4=41", <&frag0>,"brcm,function:0=4";
+                pins_40_45 = <&frag0>,"brcm,pins:0=40", <&frag0>,"brcm,pins:4=45", <&frag0>,"brcm,function:0=4";
+              };
+            };
+          '';
+        }
+      ];
+    })
+  ];
+}
diff --git a/cm4/dtb-gpio40-45.nix b/cm4/dtb-gpio40-45.nix
new file mode 100644
index 0000000..c30a0c4
--- /dev/null
+++ b/cm4/dtb-gpio40-45.nix
@@ -0,0 +1,55 @@
+{
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib) mkEnableOption mkIf mkMerge;
+  cfg = config.hardware.raspberry-pi."4".overlays;
+in {
+  options.hardware = {
+    raspberry-pi."4".overlays.spi-gpio40-45.enable = mkEnableOption ''spi-gpio40-45 enable '';
+  };
+
+  config = mkMerge [
+    (mkIf cfg.spi-gpio40-45.enable {
+      hardware.deviceTree = {
+        overlays = [
+          {
+            name = "spi-gpio40-45.overlay";
+            filter = "*rpi-cm4*";
+            dtsText = ''
+              /dts-v1/;
+              /plugin/;
+              / {
+                compatible = "brcm,bcm2711";
+                fragment@0 {
+                  target = <&spi0>;
+                  __overlay__ {
+                    cs-gpios = <&gpio 43 1>, <&gpio 44 1>, <&gpio 45 1>;
+                    status = "okay";
+                  };
+                };
+                fragment@1 {
+                  target = <&spi0_cs_pins>;
+                  __overlay__ {
+                    brcm,pins = <45 44 43>;
+                    brcm,function = <1>; /* output */
+                    status = "okay";
+                  };
+                };
+                fragment@2 {
+                  target = <&spi0_pins>;
+                  __overlay__ {
+                    brcm,pins = <40 41 42>;
+                    brcm,function = <3>; /* alt4 */
+                    status = "okay";
+                  };
+                };
+              };
+            '';
+          }
+        ];
+      };
+    })
+  ];
+}