def serve_once(self):
<EOL>request_adu = self.serial_port.read(<NUM_LIT>)<EOL>log.debug('<STR_LIT>'.format(hexlify(request_adu)))<EOL>if len(request_adu) == <NUM_LIT:0>:<EOL><INDENT>raise ValueError<EOL><DEDENT>response_adu = self.process(request_adu)<EOL>self.respond(response_adu)<EOL>
Listen and handle 1 request.