Bit-Stream Processor
25.3.4 Variables in RAM Page 5
Some additional RAM registers are placed in page 5 of the RFCORE RAM. These variables have the
prefix
PRFX
and are listed in
. The addresses overlap other RAM registers, and to access them
page 5 must be selected using the
RFRAMCFG
register; see
. Some of the registers have a
reset value. This value is written by the LLE shortly after it has been taken out of reset by
LLECTRL.LLE_EN
being set to 1. If the MCU must modify these registers, the modification must be done
each time the LLE is reset. After taking the LLE out of reset, the MCU may modify the registers after
LLASTAT.LLE_IDLE
has gone high.
Table 25-7. RAM-Based Registers in RAM Page 5
(1)
Name
Addr
Prot
Reset Val
Description
Last frequency offset estimate, read from the
0x6006
Sem1/R
–
PRFX_LAST_FREQEST
FREQEST
register at the end of receiving each
packet
0x6008
Sem1
0x20
Lower RSSI limit for use in AGC algorithm
PRFX_RSSI_LIM_LOWER
0x6009
Sem1
0x3C
Upper RSSI limit for use in AGC algorithm
PRFX_RSSI_LIM_UPPER
0x600A
Sem1
0x14
Difference between high and low RSSI gain
PRFX_RSSI_DIFF
LNAGAIN
setting to use while close to
0x600B
Sem1
0x4A
PRFX_LNAGAIN_SAT
saturation
Duration of tone in start of packet if
0x600C
–
0x600D
Sem1
0x064A
PRFX_TONE_DURATION
PRF_PKT_CONF.START_TONE
= 1,
given in 31.25-ns units
Time to subtract from Tx synthesizer calibration
0x600E
–
0x600F
Sem0
0x0600
PRFX_TONE_OFFSET
time if
PRF_PKT_CONF.START_TONE
=
1, given in 31.25-ns units
(1)
Note that the LLE is reset when the device enters PM2 or PM3. This means that the PRFX registers must be re-initialized after
coming up from one of these power modes.
The parts of RAM page 5 that are not listed in
are reserved for use by the LLE and should not
be written by the MCU.
25.4 Bit-Stream Processor
The bit-stream processor (BSP) supports automatic insertion of CRC and detection of CRC error with a
programmable polynomial of 8, 16, 24, or 32 bits.
The bit-stream processor also supports whitening and de-whitening. The whitening sequences
supported are a PN7 sequence and a PN 9 sequence compatible with CC2500/CC2510.
The bit-stream processor is used by the LLE to do the whitening and CRC generation and checking. This
operation is based on the configuration set up by the MCU. The BSP can also be run in a coprocessor
mode to calculate whitened sequences and CRCs. This must only be done while the LLE is not running.
25.4.1 Whitening
The BSP supports two whiteners, a PN7 and a PN9 whitener. The register
BSP_MODE
is used to enable or
disable each whitener. When no whitener is enabled, it outputs zero. The whitener sequence is XORed
with the transmitted or received signal.
It is possible to enable both whiteners. This is useful, e.g., in conjunction with the test command
CMD_TX_TEST (
) to transmit a white test signal.
25.4.1.1 PN7 Whitening
The PN7 whitener is shown in
. It has a 7-bit whitening shift register w used for calculating the
PN sequence given by the polynomial x
7
+ x
4
+ 1. The output is the same as the shift register feedback.
304
CC2541 Proprietary Mode Radio
SWRU191C
–
April 2009
–
Revised January 2012
Copyright
©
2009
–
2012, Texas Instruments Incorporated