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Link Layer Engine
If PRFX_TONE_DURATION is set too large compared to the number of preamble bytes configured, the
modulator underflows. If this happens, the task ends with TASKERR_MODUNF as end cause.
Table 25-15. Recommended RAM Register Settings for Start Tone
Data Rate
PRFX_TONE_DURATION PRFX_TONE_OFFSET
MDMCTRL2.NUM_PREAM_BYTES × 0x80 +
2 Mbps
MDMCTRL2.NUM_PREAM_BYTES × 0x80
0x4A
MDMCTRL2.NUM_PREAM_BYTES × 0x100 +
1 Mbps
MDMCTRL2.NUM_PREAM_BYTES × 0x100
0x52
MDMCTRL2.NUM_PREAM_BYTES × 0x200 + min(MDMCTRL2.NUM_PREAM_BYTES × 0x200,
500 kbps
0x62 0x1000)
MDMCTRL2.NUM_PREAM_BYTES × 0x400 + min(MDMCTRL2.NUM_PREAM_BYTES × 0x400,
250 kbps
0x82 0x1000)
25.9.2.3 Receive Task
When a CMD_RX command is received, the LLE configures the radio on the channel given by
PRF_CHAN.FREQ and starts listening for a sync word.
The LLE can set up an internal time-out for the sync search in the PRF_SEARCH_TIME register. If this
register is non-zero and no sync has been obtained in the number of 32 MHz cycles given by this register,
the task ends with a TASK_NOSYNC end cause. Note that the value of this register must be large enough
to have time for the duration of the sync word and one preamble byte, in addition to some margin, in order
to get sync. The task can also be set up to end on Timer 2 event 2, based on
PRF_TASK_CONF.STOP_CONF. If this bit field is 11, the Timer 2 event 2 time-out applies only during the
first sync search after a CMD_RX command has been issued if PRF_TASK_CONF.START_CONF is 0. In
this case, the time-out in PRF_SEARCH_TIME does not apply to the first sync search, but it still applies to
subsequent sync searches in the same task. If PRF_TASK_CONF.STOP_CONF is 11 and
PRF_TASK_CONF.START_CONF is 1, the time-out applies to every sync search and PRF_SEARCH_TIME
never applies, but the Timer 2 event 2 timeout does not apply after sync is obtained or while waiting for
Timer 2 event 1 to restart listening. If sync is obtained, the LLE starts reading the packet.
If sync is found on a packet, the time of sync is captured by the Timer 2 capture function (see
Section 22.1.10).
25.9.2.3.1 Basic Mode
This section describes the receive operation if PRF_TASK_CONF.MODE is 00 or 01.
If PRF_TASK_CONF.MODE is 01, the length byte is read first. It gives the number of bytes between the
length byte and the CRC, including the address. If the length is too small to contain the address, the
reception of the packet is stopped and the device goes back to sync search (regardless of the setting in
PRF_TASK_CONF.REPEAT).
Next, the address byte is read if PRF_PKT_CONF.ADDR_LEN is 1. It is compared against
PRF_ADDR_ENTRYn.ADDRESS for the values of n where the entry is enabled for the received sync word.
If there is a matching entry, this entry is used when receiving the packet; otherwise, reception is stopped
and the device goes back to sync search. If PRF_PKT_CONF.ADDR_LEN is 0, the first entry that is enabled
for the received sync word is used. If PRF_TASK_CONF.MODE is 00, the packet length is then read from
PRF_ADDR_ENTRYn.RXLENGTH. This length includes the address, so it must be greater than or equal to
the number of address bytes. If PRF_TASK_CONF.MODE is 01, the received length byte is compared
against PRF_ADDR_ENTRYn.RXLENGTH. If it is greater than that value, reception is stopped and the
device goes back to sync search.
If reception is stopped due to address mismatch or invalid length, the time-out given by
PRF_SEARCH_TIME or Timer 2 event 2 still applies. If the first packet of the task is being received and
PRF_TASK_CONF.STOP_CONF is 11, the next packet still counts as the first packet.
319
SWRU191C–April 2009–Revised January 2012 CC2541 Proprietary Mode Radio
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