[core] Add lt_get_device_mac() function

cores/common/base/api/lt_cpu.h

@@ -38,6 +38,7 @@ uint32_t lt_cpu_get_unique_id();
 /**
  * @brief Get CPU ID based on the last three octets of MAC address.
  * Note: the number is 24-bit (with the MSB being zero).
+ * The 3rd-to-last octet is least-significant, the last octet is most-significant.
  */
 uint32_t lt_cpu_get_mac_id();
 

cores/common/base/api/lt_device.h

@@ -20,6 +20,13 @@ const char *lt_get_board_code();
  */
 const char *lt_get_device_name();
 
+/**
+ * @brief Read device's *default* MAC address into 'mac' array.
+ * This can be used even without Wi-Fi enabled, and will ignore
+ * user-changed Wi-Fi MAC (if changing is possible).
+ */
+void lt_get_device_mac(uint8_t *mac);
+
 /**
  * @brief Reboot the CPU.
  */

cores/common/base/lt_api.c

@@ -39,6 +39,12 @@ __attribute__((weak)) uint32_t lt_cpu_get_unique_id() {
 	return lt_cpu_get_mac_id();
 }
 
+__attribute__((weak)) uint32_t lt_cpu_get_mac_id() {
+	uint8_t mac[6];
+	lt_get_device_mac(mac);
+	return (mac[3] << 0) | (mac[4] << 8) | (mac[5] << 16);
+}
+
 __attribute__((weak)) uint8_t lt_cpu_get_core_count() {
 	return 1;
 }