ESP32 ESP.getChipId() alternative

get_chip_id.cpp

#include <Esp.h>
#include <byteswap.h>

// Get the lower 3 bytes of 6 byte MAC
// aa:bb:cc:dd:ee:ff -> dd:ee:ff
// (3 byte shift, byte-swap and 1 byte shift)
uint32_t partialMac = __bswap_32(ESP.getEfuseMac() >> 24) >> 8;
String clientId = String("eee-") + String(partialMac, HEX);

uint32_t getChipId(){
  return __bswap_32(ESP.getEfuseMac() >> 24) >> 8;
}