Add ESP.getChipId() function to get ESP32's ChipID. (#322)

* Add ESP.getChipId() function to get ESP32's ChipID.

* change getChipId() to getEfuseMac()

cores/esp32/Esp.cpp

@@ -212,3 +212,11 @@ bool EspClass::flashRead(uint32_t offset, uint32_t *data, size_t size)
 {
     return spi_flash_read(offset, (uint32_t*) data, size) == ESP_OK;
 }
+
+
+uint64_t EspClass::getEfuseMac(void)
+{
+    uint64_t _chipmacid;
+    esp_efuse_read_mac((uint8_t*) (&_chipmacid));
+    return _chipmacid;
+}

cores/esp32/Esp.h

@@ -76,6 +76,8 @@ public:
     bool flashWrite(uint32_t offset, uint32_t *data, size_t size);
     bool flashRead(uint32_t offset, uint32_t *data, size_t size);
 
+    uint64_t getEfuseMac();
+
 };
 
 extern EspClass ESP;

libraries/ESP32/examples/ChipID/GetChipID/GetChipID.ino

@@ -0,0 +1,14 @@
+uint64_t chipid;  
+
+void setup() {
+	Serial.begin(115200);
+}
+
+void loop() {
+	chipid=ESP.getEfuseMac();//The chip ID is essentially its MAC address(length: 6 bytes).
+	Serial.printf("ESP32 Chip ID = %04X",(uint16_t)(chipid>>32));//print High 2 bytes
+	Serial.printf("%08X\n",(uint32_t)chipid);//print Low 4bytes.
+
+	delay(3000);
+
+}