Keyboard functional and first sending of PGN 127502

include/main.h

@@ -6,6 +6,7 @@
 
 // NMEA2000 defaults
 #define N2K_DEFAULT_NODEID 124
+#define NMEA2000_HEARTBEAT_INTERVAL 5000 // milliseconds
 
 // Keys
 #define KEY_1 GPIO_NUM_5     // D2
@@ -54,3 +55,24 @@
 #define SPI_MISO GPIO_NUM_47 // D12
 #define SPI_SCK GPIO_NUM_48  // D13
 #define SPI_CS GPIO_NUM_46   // B0
+
+// Button indices
+#define BUTTON_1 0
+#define BUTTON_2 1
+#define BUTTON_3 2
+#define BUTTON_4 3
+#define BUTTON_5 4
+#define BUTTON_6 5
+#define BUTTON_DST 6
+
+enum class ButtonPressType : uint8_t
+{
+    SHORT,  // < 1 second
+    MEDIUM, // >= 1 second and < 3 seconds
+    LONG    // >= 3 seconds
+};
+struct ButtonEvent
+{
+    uint8_t buttonId;
+    ButtonPressType pressType;
+};