57
8168C-MCU Wireless-02/10
AT86RF212
Table 5-15. TX_ARET Interpretation of TRAC_STATUS Register Bits
Value
Name
Description
0
SUCCESS
The transaction was responded by a valid
ACK, or, if no ACK is requested, after a
successful frame transmission.
1
SUCCESS_DATA_PENDING
Equivalent to SUCCESS and indicating that
the “Frame Pending” bit (see section
6.1.2.2)
of the received acknowledgment frame was
set.
3
CHANNEL_ACCESS_FAILURE
Channel is still busy after
MAX_CSMA_RETRIES of CSMA-CA.
5
NO_ACK
No acknowledgement frame was received
during all retry attempts.
7
INVALID
Entering TX_ARET mode until IRQ_3
(TRX_END).
A value of MAX_CSMA_RETRIES = 7 initiates an immediate TX_ARET transaction
without performing CSMA-CA. This supports beacon-enabled network operation.
Furthermore, by ignoring the value of MAX_FRAME_RETRIES, only a single attempt is
made to transmit the frame.
Note that the acknowledgment receive procedure does not overwrite the Frame Buffer
content. Transmit data in the Frame Buffer is not modified during the entire TX_ARET
transaction. Received frames, other than the expected ACK frame, are discarded
automatically.
5.2.4.1 Acknowledgment Timeout
If an acknowledgment (ACK) frame is expected after frame transmission, the
AT86RF212 sets a timeout until which a valid ACK frame must have been arrived. This
timeout macAckWaitDuration is defined according to [2] as follows:
macAckWaitDuration [symbol periods] =
aUnitBackoffPeriod + aTurnaroundTime + phySHRDuration + 6
phySymbolsPerOctet
where 6 represents the number of PHY header octets plus the number of PSDU octets
in an acknowledgment frame.
Specifically for the implemented PHY Modes (see section
7.1), this formula results in
the following values:
BPSK:
macAckWaitDuration = 120 symbol periods
O-QPSK:
macAckWaitDuration = 54 symbol periods
Note that for any PHY Mode the unit “symbol period” refers to the symbol duration of
the appropriate synchronization header; see section
7.1.3 for further information
regarding symbol period.
5.2.4.2 Timing
A timing example of a TX_ARET transaction is shown in
Figure 5-13. In the example
shown, a data frame with an acknowledgment request is to be transmitted. The frame
transmission is started by pin 11 (SLP_TR). As MIN_BE is set to zero, the initial
CSMA-CA backoff period has length zero too. Thus, the CSMA-CA duration time
tCSMA-CA only consists of 8 symbols of CCA measurement period. If CCA returns IDLE
(assumed here), the frame is transmitted.