Initial code

app/boards/shields/mach3/Kconfig.defconfig

@@ -0,0 +1,6 @@
+if SHIELD_MACH3
+
+config ZMK_KEYBOARD_NAME
+    default "MACH3"
+
+endif # BOARD_MACH3

app/boards/shields/mach3/Kconfig.shield

@@ -0,0 +1,2 @@
+config SHIELD_MACH3
+    def_bool $(shields_list_contains,MACH3)

app/boards/shields/mach3/mach3.keymap

@@ -0,0 +1,22 @@
+#include <behaviors.dtsi>
+#include <dt-bindings/zmk/keys.h>
+#include <dt-bindings/zmk/bt.h>
+
+/ {
+    keymap {
+        compatible = "zmk,keymap";
+
+        default_layer {
+// -----------------------------
+// |   A   |    B    |    C    |
+// |   D   |    E    |    F    |
+// |   G   |    H    |    I    |
+// -----------------------------
+            bindings = <
+    &kp A    &kp B    &kp C
+    &kp D    &kp E    &kp F
+    &kp G    &kp H    &kp I
+            >;
+        };
+    };
+};

app/boards/shields/mach3/mach3.overlay

@@ -0,0 +1,23 @@
+/ {
+    chosen {
+        zmk,kscan = &kscan0;
+    };
+
+    kscan0: kscan_0 {
+        compatible = "zmk,kscan-gpio-matrix";
+        label = "KSCAN";
+        diode-direction = "col2row";
+
+        col-gpios
+            = <&pro_micro 7 GPIO_ACTIVE_HIGH>
+            , <&pro_micro 8 GPIO_ACTIVE_HIGH>
+            , <&pro_micro 9 GPIO_ACTIVE_HIGH>
+            ;
+
+        row-gpios
+            = <&pro_micro 2 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>
+            , <&pro_micro 3 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>
+            , <&pro_micro 4 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>
+            ;
+    };
+};

app/boards/shields/mach3/mach3.zmk.yml

@@ -0,0 +1,11 @@
+file_format: "1"
+id: MACH3
+name: MACH3
+type: shield
+url: https://machkeyboards.com
+requires: [pro_micro]
+features:
+  - keys
+outputs:
+  - usb
+  - ble