docs: def read_mac(self):
          """ Read MAC from OTP ROM """
          mac0 = self.read_reg(self.ESP_OTP_MAC0)
          mac1 = self.read_reg(self.ESP_OTP_MAC1)
          mac3 = self.read_reg(self.ESP_OTP_MAC3)
          if (mac3 != 0):
              oui = ((mac3 >> 16) & 0xff, (mac3 >> 8) & 0xff, mac3 & 0xff)
          elif ((mac1 >> 16) & 0xff) == 0:
              oui = (0x18, 0xfe, 0x34)
          elif ((mac1 >> 16) & 0xff) == 1:
              oui = (0xac, 0xd0, 0x74)
          else:
              raise FatalError("Unknown OUI")
          return oui + ((mac1 >> 8) & 0xff, mac1 & 0xff, (mac0 >> 24) & 0xff)