Transmit a message to the CAN bus.

        :param can.Message msg: A message object.
        :param float timeout:
            Wait up to this many seconds for the transmit queue to be ready.
            If not given, the call may fail immediately.

        :raises can.CanError:
            if the message could not be written.

def send(self, msg, timeout=None):
        """Transmit a message to the CAN bus.

        :param can.Message msg: A message object.
        :param float timeout:
            Wait up to this many seconds for the transmit queue to be ready.
            If not given, the call may fail immediately.

        :raises can.CanError:
            if the message could not be written.
        """
        log.debug("We've been asked to write a message to the bus")
        logger_tx = log.getChild("tx")
        logger_tx.debug("sending: %s", msg)

        started = time.time()
        # If no timeout is given, poll for availability
        if timeout is None:
            timeout = 0
        time_left = timeout
        data = build_can_frame(msg)

        while time_left >= 0:
            # Wait for write availability
            ready = select.select([], [self.socket], [], time_left)[1]
            if not ready:
                # Timeout
                break
            sent = self._send_once(data, msg.channel)
            if sent == len(data):
                return
            # Not all data were sent, try again with remaining data
            data = data[sent:]
            time_left = timeout - (time.time() - started)

        raise can.CanError("Transmit buffer full")