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Table 16-5. Writing Sequence for Encryption Engine Initialization (Continued)
16.3.1.3.3 Whitening/De-Whitening
According to the Bluetooth specifications, all packets must be scrambled to randomize the data from
highly redundant patterns and to minimize DC bias in the packet. The whitening unit performs this
scrambling (whitening) and descrambling (de-whitening) of the packet header and payload (including the
CRC) during transmit and receive.
Whitening is enabled or disabled by software. To enable whitening, write the initialization word specified
in the Bluetooth standard to the WHITE_CONTROL register. To disable, write all zeros to the same
register. There is no status information available for the whitening/de-whitening unit.
16.3.1.3.4 FEC Coding/Decoding
The forward error correction (FEC) is a standard block encoder/decoder algorithm. Two forms of FEC are
used in the Bluetooth standard:
•
1/3 FEC: Repeating each bit so that each bit occurs three times in a row. Simple majority decision
is used in decoding—that is, if two or more bits are equal, the value of these bits is used.
•
2/3 FEC: Using a (15, 10) shortened Hamming code with a minimum distance of 4. This encoding
allows correction of one-bit errors and detection of two-bit errors. For each block of 10 bits, 5
redundant bits are appended. In the receive decoding, the BTA checks each 15 bit block for errors
and sets the REC2 and NREC flags in the status register accordingly.
FEC can be enabled or disabled by software according to the packet type.
16.3.1.4 Bit Buffer
The bit buffer is a 512-bit memory bank used for four different purposes. It is software accessible, and is
arranged as eight 64-bit "long words," designated LW0 through LW7. Software views each long word as
four concatenated 16 bit words that are accessed independently. Figure 16-4 illustrates the arrangement of
the long words in the bit buffer.
MOTOROLA
Word Number
Bits 15–8
11
CL[1]
12
111000CL
Bluetooth Accelerator (BTA)
Bits 7–0
CL[0]
CL
CL[2]
25
24
Module Descriptions
16-11
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