Frame Transmission (TX_ARET)

This section describes how frames are transmitted in the TX_ARET mode.

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PHY_DATA_REQUEST_TX_ARET

The TX_ARET mode frame transmission combines a hardware assisted CCA followed by the frame transmission itself and the ACK frame checking. Therefore the radio transceiver switches internally between transmit and receive states.

The result of a TX_ARET transaction is stored in the sub register SR_TRAC_STATUS after the TRX_IRQ_TRX_END interrupt.

Return values:

tracstat

Result of a TX_ARET transaction from sub register SR_TRAC_STATUS. TRAC_SUCCESS : frame transmission was successful and if an ACK frame was required, it was received correctly. TRAC_SUCCESS_DATA_PENDING : Frame transmission was successful. In the received ACK frame, the frame pending subfield was set to 1. TRAC_CHANNEL_ACCESS_FAILURE : The CCA algorithm has failed and the frame could not be send. TRAC_NO_ACK : A correct ACK frame was not received within the required period of time. TRAC_INVALID : transaction ongoing or aborted

According to 802.15.4-2003 (see Table 71, macAckWaitDuration=54 Symbols for 2.4GHz), the ACK frame needs to be received within an interval of 864 us. The internal timing for the ACK frame processing in TX_ARET mode is shown below:

 = CCA =:=== TX ===:============== RX ====================
                   0             42  44  46  48  50  52  54 [time /symbols]
               +---|          |---+---+---+---+---+---+---|
 -------|~~~~~~| F |----------|SFD|LEN|    ACK    |  FCS  | --------------->
        |      +---|          |---o---+---+---+---+---+---|
        |          |              |                       |
        t0         t1             t2                      t3

         F = last transmitted byte,
         SFD, LEN, ACK, FCS = data of the received ACK frame

• t0 : If all CCA attempts fail, at this point in time an TRX_IRQ_TRX_END interrupt is generated with tracstat=TRAC_CHANNEL_ACCESS_FAILURE.
• t1 : End of the frame transmission.
• t2 : A TRX_IRQ_TRX_END interrupt is generated with tracstat=TRAC_NO_ACK, if no SFD occurs within 54 symbols after the last transmission attempt.
• t3 : For a succesfull TX_ARET transaction the TRX_IRQ_TRX_END interrupt is generated at this point in time (tracstat=TRAC_SUCCESS if ACK frame was valid; tracstat=TRAC_SUCCESS_DATA_PENDING if ACK was valid and frame pending bit was set in the ACK frame).

Note:

After a TX_ARET transaction the frame is kept in the SRAM, so that it can sent out another time. The received ACK frame is processed internally and therefore it is not stored in the SRAM.

If the check for BUSY_TX_ARET after initiating the transmission fails, the transmission shall be initiated again. If the frame was downloaded before toggling pin TRX_PIN_SLP_TR, the frame shall also be downloaded again.

Code example

    trx_pinset_slptr(1);
    delay_ns(65);
    trx_pinset_slptr(0);
    trxstat = trx_bit_read(SR_TRX_STATUS);
    ASSERT(trxstat==BUSY_TX_ARET);
    trx_frame_write(len(frame), frame);
    /* TRX_IRQ_TRX_END occurs here */
    tracstat = trx_bit_read(SR_TRAC_STATUS);

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