Texas Instruments SimpleLink CC2620 Technical Reference Manual page 1537

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23.5.4.3 CSMA-CA Operation
The CSMA-CA operation is a foreground-level operation that runs on top of a receive or energy-detect
scan operation. If run on top of an energy-detect scan operation, this does not perform the energy-detect
scan procedure, but starts a receiver without having to receive packets. This operation starts with the
CMD_IEEE_CSMA command, and uses the command structure given in
At the start of a CSMA-CA operation, the radio CPU waits for the start trigger.
The radio CPU maintains a variable CW which initializes to csmaConfig.initCW.
If remainingPeriods is nonzero at the start of the command, the radio CPU delays for that number of
backoff periods (default 320 µs) measured from the start trigger before proceeding. Otherwise, the radio
CPU draws a pseudo-random number in the range 0 to 2
radio CPU then waits that number of backoff periods from the start trigger before proceeding.
After this wait time, the radio CPU checks the CCA state from the background-level operation, as in
Section 23.5.4.1.5. If the CCA state was INVALID, the radio CPU waits before trying again. If
csmaConfig.bSlotted = 1, the wait is for one backoff period, otherwise it waits until an RSSI result is
available. If the CCA state was IDLE, the radio CPU decrements CW by 1, and if this results in a value of
zero, the CSMA-CA operation ends with success. If this results in a nonzero value, the radio CPU waits
one backoff period timed from the end of the wait time, and then checks the CCA state again as described
previously.
SWCU117C – February 2015 – Revised September 2015
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Table 23-61.
(BE)–1
, where BE is given by
IEEE 802.15.4
(Table 23-61). The
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Radio