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If CMD_STOP is received while transmitting a packet, waiting for transmission of another packet, waiting
for an ACK, 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
CMD_STOP is received while waiting for Timer 2 event 1 to restart reception, the task ends immediately
with TASK_STOP as the end cause.
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: Behaves as if a CMD_STOP was received
• 10: Behaves as if a CMD_SHUTDOWN was received
• 11: Nothing happens.
In addition, the task can end for reasons described earlier, or it can end due to an error condition. The full
list of possible end causes is summarized in Table 25-20.
Table 25-20. End-of-Transmit Tasks
Condition End-of-Task Cause Comment
Transmitted packet (and potentially received ACK)
TASK_ENDOK
with PRF_TASK_CONF.REPEAT = 0
Transmitted packet (and potentially received ACK)
TASK_ENDOK
and observed Tx FIFO with no available data
Transmitted packet (and potentially received ACK)
after having observed CMD_STOP or Timer 2 event 2
TASK_STOP
with PRF_TASK_CONF.STOP_CONF = 01
Did not get valid acknowledgment after having
retransmitted the number of times given by
TASK_MAXRT
PRF_RETRANS_CNT
Observed empty Tx FIFO when packet transmission
LLEERR and RXTXABO interrupts are
TASKERR_TXFIFO
is supposed to start, or Tx FIFO is in an invalid state
also raised.
Rx FIFO went overfull while receiving an ACK that
TASKERR_RXFIFO
RXFIFOFULL interrupt is also raised.
was not otherwise to be discarded
Received command for starting new task or
If transmitter was running, an RXTXABO
CMD_SHUTDOWN or observed Timer 2 event 2 with
TASK_ABORT
interrupt is also raised.
PRF_TASK_CONF.STOP_CONF = 10
LLEERR interrupt is also raised. If
transmitter or receiver was running and
Received unknown command TASKERR_CMD
had obtained sync, an RXTXABO
interrupt is also raised.
Task ends without any radio operation.
Semaphore is not free when expected TASKERR_SEM
LLEERR interrupt is also raised.
Invalid value of RAM register TASKERR_PAR
LLEERR interrupt is also raised.
Length field to be transmitted exceeded maximum
allowed value (255 in basic mode, 127 or 63 in auto TASKERR_PAR
LLEERR interrupt is also raised.
mode with variable length)
25.9.2.5 Transmit on Clear-Channel Task
When a CMD_TX_ON_CC command is received, the LLE configures the receiver on the channel given by
PRF_CHAN.FREQ, but sync search is not enabled. The LLE polls the RSSI register every 5.33 µs and
compares it to the value of PRF_RSSI_LIMIT. If a valid RSSI below the value of PRF_RSSI_LIMIT is
observed more than PRF_RSSI_COUNT times in a row, the system starts transmitting. From there, the
operation is as a normal transmit task, see Section 25.9.2.4, except for the operation after a packet has
been transmitted and potentially acknowledged, which is described in Section 25.9.2.5.1.
326
CC2541 Proprietary Mode Radio SWRU191C– April 2009–Revised January 2012
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