Texas Instruments CC253x User Manual

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25.9.2.5.1 Continuation and Ending of Transmit on Clear-Channel Tasks
If PRF_TASK_CONF.TX_ON_CC_CONF is 1, the task ends if a valid RSSI value is not below the limit. If
PRF_TASK_CONF.TX_ON_CC_CONF is 0, the device keeps listening until an RSSI below the given value
is found.
If PRF_TASK_CONF.STOP_CONF is 11, Timer 2 event 2 may give a time-out while listening for a clear
channel the first time, but not after the first transmission has been started.
If PRF_TASK_CONF.TX_ON_CC_CONF is 0, the clear-channel assessment must not be used as the only
medium access control scheme in a multiuser environment, as this may cause all the devices to start
transmission at the same time.
If retransmission is enabled, the LLE listens for acknowledgment and retransmits if needed as for normal
Tx tasks. However, if PRF_TASK_CONF.REPEAT_CONF is 0 after applying the retransmit delay, the device
returns to listening, performing the same operation as when the task started, before possibly
retransmitting.
If PRF_TASK_CONF.REPEAT is 0, the task ends after transmission as for normal Tx tasks.
If PRF_TASK_CONF.REPEAT is 1, the Tx FIFO status is checked. If the Tx FIFO has no available data, the
task ends with TASK_ENDOK as the end cause. Otherwise, transmission restarts. If
PRF_TASK_CONF.REPEAT_CONF is 0, the task returns to listening, whereas if it is 1, the task restarts as if
it were a standard transmit task. If PRF_TASK_CONF.START_CONF is 1, it behaves as if the task was
started again with the LLE waiting for Timer 2 event 1, then performing a synthesizer calibration and
starting to listen or transmit. If PRF_TASK_CONF.START_CONF is 0, the listening or transmission restarts
PRF_TX_DELAY after the end of the previously transmitted packet, with synthesizer recalibration only if
there is enough time, but in other respects as starting a new task.
If Timer 2 event 2 (either from Timer 2 or from CMD_SEND_EVENT2) is observed during the task, the
behavior depends on PRF_TASK_CONF.STOP_CONF.
• 00: Nothing happens.
• 01: If received while transmitting a packet or waiting for or receiving an ACK or in the transition
between those, the task ends with TASK_STOP as the end cause after the packet is fully transmitted
and (if ACK is expected) the ACK is received or given up. If received while waiting for Timer 2 event 1
to restart reception, the task ends immediately with TASK_STOP as the end cause.
• 10: Behaves as if a CMD_SHUTDOWN was received
• 11: If received while listening for RSSI below the level before the first packet after the task was started,
or if PRF_TASK_CONF.START_CONF is 1 while listening before any packet, the task ends immediately
with TASK_NOCC as the end cause. Otherwise, nothing happens.
The task can end for all the same reasons as a normal transmit task summarized in Table 25-20. In
addition it can end for the reasons listed in Table 25-21.
Table 25-21. Additional Reasons for End-of-Transmit on Clear-Channel Tasks
Condition End-of-Task Cause Comment
Observed valid RSSI above the threshold with
TASK_NOCC
PRF_TASK_CONF.TX_ON_CC_CONF = 1
Observed CMD_STOP or Timer 2 event 2 with
PRF_TASK_CONF.STOP_CONF = 01 or 11 while listening for
TASK_NOCC
RSSI below the threshold
25.9.2.6 Timing
The timing in tasks is given the registers PRF_TX_DELAY, PRF_SEARCH_TIME, and
PRF_RETRANS_DELAY, PRF_SEARCH_TIME, PRF_RX_TX_TIME, and PRF_TX_RX_TIME. The first two of
these registers are multiplied by 2 and then represent the number of 32-MHz samples, while the rest
directly give the number of 32-MHz samples. PRF_TX_DELAY gives the time from the end of the previous
transmission in the task to the start of the next transmission. Some examples of these delays are shown in
Figure 25-12 and Figure 25-13 for Rx and Tx tasks, respectively. The time from the end of a received
packet to the beginning of a transmitted packet is 130 µs in an Rx task with auto ACK.
327
SWRU191C–April 2009–Revised January 2012 CC2541 Proprietary Mode Radio
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Texas Instruments CC253x Specifications

General

Brand	Texas Instruments
Model	CC253x
Category	Microcontrollers
Language	English