code: def to_string(self):
          
          fmt = '<BBH'
          first = struct.pack(
              fmt,
              self._mode,
              self._cr_timeout,
              self._auto_eject_time
          )
  
          #crc = 0xffff - yubico_util.crc16(first)
          #second = first + struct.pack('<H', crc)
          return first
docs: Return the current DEVICE_CONFIG as a string (always 4 bytes).