Add a single or block register transfer operation to this command

def add(self, count, request, data, dap_index):
        """
        Add a single or block register transfer operation to this command
        """
        assert self._data_encoded is False
        if self._dap_index is None:
            self._dap_index = dap_index
        assert self._dap_index == dap_index

        if self._block_request is None:
            self._block_request = request
        elif request != self._block_request:
            self._block_allowed = False
        assert not self._block_allowed or self._block_request == request

        if request & READ:
            self._read_count += count
        else:
            self._write_count += count
        self._data.append((count, request, data))

        if LOG_PACKET_BUILDS:
            self._logger.debug("add(%d, %02x:%s) -> [wc=%d, rc=%d, ba=%d]" %
                (count, request, 'r' if (request & READ) else 'w', self._write_count, self._read_count, self._block_allowed))