def listen_tta(self, target, timeout):
        """Listen as Type A Target.

        Waits to receive a SENS_REQ command at the bitrate set by
        **target.brty** and sends the **target.sens_res**
        response. Depending on the SENS_RES bytes, the Initiator then
        sends an RID_CMD (SENS_RES coded for a Type 1 Tag) or SDD_REQ
        and SEL_REQ (SENS_RES coded for a Type 2/4 Tag). Responses are
        then generated from the **rid_res** or **sdd_res** and
        **sel_res** attributes in *target*.

        Note that none of the currently supported hardware can
        actually receive an RID_CMD, thus Type 1 Tag emulation is
        impossible.

        Arguments:

          target (nfc.clf.LocalTarget): Supplies bitrate and mandatory
            response data to reply when being discovered.

          timeout (float): The maximum number of seconds to wait for a
            discovery command.

        Returns:

          nfc.clf.LocalTarget: Command data received from the remote
            Initiator if being discovered and to the extent supported
            by the device. The first command received after discovery
            is returned as one of the **tt1_cmd**, **tt2_cmd** or
            **tt4_cmd** attribute (note that unset attributes are
            always None).

        Raises:

          nfc.clf.UnsupportedTargetError: The method is not supported
            or the *target* argument requested an unsupported bitrate
            (or has a wrong technology type identifier).

          ~exceptions.ValueError: A required target response attribute
            is not present or does not supply the number of bytes
            expected.

        """
        fname = "listen_tta"
        cname = self.__class__.__module__ + '.' + self.__class__.__name__
        raise NotImplementedError("%s.%s() is required" % (cname, fname))