Texas Instruments SimpleLink CC2620 Technical Reference Manual page 1535

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23.5.4.1.4 End of Receive Operation
The receive operation can end as a result of the end trigger given by endTrigger and endTime, or by a
command. The commands that can end the receive operation are the immediate commands
CMD_ABORT and CMD_STOP, and the foreground-level radio operation command
CMD_IEEE_ABORT_BG. The end-trigger and the CMD_STOP command cause the receiver to keep
running until the end of the frame, or until the reception would otherwise be stopped if observed while a
packet was being received. The CMD_ABORT and CMD_IEEE_ABORT_BG commands cause the
receiver to stop as quickly as the implementation allows.
A receive operation ends through one of the causes listed in
structure after the command has ended indicates the reason why the operation ended. In all cases, a
COMMAND_DONE interrupt is raised. In each case, the result is indicated as TRUE, FALSE, or ABORT.
This decides whether to start the next command (if any) indicated in pNextOp, or to return to an IDLE
state. Before the receive operation ends, the radio CPU writes the maximum observed RSSI during the
receive operation to pOutput->maxRssi.
If a transmit operation is started in the foreground, the receive operation is suspended. The receiver stops
as when aborted, but the synthesizer is left on to the extent possible when switching to transmit mode.
When the receiver has stopped, the status field of the command structure is set to IEEE_SUSPENDED.
When the transmit command is done, the receiver restarts and the status field of the command structure is
set back to RUNNING.
Condition
Observed end trigger and finished any ongoing reception
Received CMD_STOP
Received CMD_ABORT or CMD_IEEE_ABORT_BG
Observed illegal parameter
23.5.4.1.5 CCA Monitoring
While the receiver is running, the radio CPU monitors some signals for use in clear-channel assessment.
This monitoring is controlled by ccaOpt. There are three sources for CCA: RSSI above level (ccaEnergy),
carrier sense based on the correlation value (ccaCorr), and carrier sense based on sync found (ccaSync).
Each of these may have the state BUSY, IDLE, or INVALID.
The RSSI above-level is maintained by monitoring the RSSI. If the RSSI is greater than or equal to
ccaRssiThr, ccaEnergy is busy. If the RSSI is smaller than ccaRssiThr, ccaEnergy is IDLE. When an RSSI
calculation has not yet been completed since the receiver started, ccaEnergy is INVALID.
The carrier-sense monitoring based on correlation value uses correlation peaks as defined for use in the
SFD search algorithm in the receiver. If the number of correlation peaks observed in the last 8-symbol
periods (32 µs) is greater than ccaOpt.corrThr, ccaCorr is BUSY; otherwise ccaCorr is IDLE. The value of
ccaOpt.corrThr can be from 0 to 3. While the receiver is receiving a frame, ccaCorr is BUSY regardless of
the observed correlation peaks. If the time since the receiver started is less than 8 symbol periods and the
number of correlation peaks observed since the receiver started is less than or equal to ccaOpt.corrThr,
ccaCorr is INVALID.
The carrier-sense monitoring based on sync found is maintained by the radio CPU as follows. If sync is
obtained on the receiver, the radio CPU checks the PHY header to find the frame length. The radio CPU
considers the channel to be busy for the duration of this frame. This check is done even if reception of the
frame is stopped due to the frame filtering and sync search is restarted. If sync is found again while the
channel is viewed as BUSY, the channel is viewed as Busy until both these frames have ended according
to the observed frame lengths. The INVALID state is not used for ccaSync.
If the radio is transmitting an ACK or is suspended for running a TX operation, ccaEnergy, ccaCorr, and
ccaSync are all BUSY.
SWCU117C – February 2015 – Revised September 2015
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Table 23-81. End of Receive Operation
Status Code
IEEE_DONE_OK
IEEE_DONE_STOPPED
IEEE_DONE_ABORT
IEEE_ERROR_PAR
Copyright © 2015, Texas Instruments Incorporated
Table 23-81. The status field of the command
IEEE 802.15.4
Result
TRUE
FALSE
ABORT
ABORT
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