Gsm Fire Encode - Motorola DSP56305 User Manual

CFBTA and CFFTA, respectively. In general, coefficients g
input into bit (48–a) of CFBTA/B and CFFTA/B, respectively. The polynomial degree, n,
is input by setting bit (48–n) of CMSKA/B while all other bits are cleared. The
parameter, m , is determined by the values of bits INE0 and INE1 in CSFTB. If m
0
then INE0 = INE1 = 1, and if m
the feedforward path is always enabled and not affected by INE0/INE1 bits.
14.7.2

GSM Fire Encode

In GSM, Fire coding is defined for burst error correction of 12 bits. Fire encode makes use
of the following generator polynomial of degree 40:
( ) (
G D = D
Fire encode processing involves calculating a CRC syndrome on the data block using the
polynomial G(D). The CCOP is configured in the Parity Coding mode using two
concatenated CFSRs (OPM[1:0] = 11) as shown in Figure 14-10.
Data
Input
'0'
23 22 21
Feedback Tap 0010 0000 0000 0000 1000 0010
Feedfwd Tap 0000 0000 0000 0000 0000 0000
Feedback Tap
23 22 21
Feedback Tap 0100 0000 0000 0000 0000 0000
Feedfwd Tap 0000 0000 0000 0000 0000 0000
MOTOROLA
= 0, then INE0 = INE1 = 0. Notice that the input data to
0
23 17 3
) × (
+ 1 D + D
20 19 18 17 16 15 14
CFSRA
20 19 18 17 16 15
Figure 14-10 GSM Fire Encode
DSP56305 User's Manual
CYCLIC CODE CO-PROCESSOR
a
40 26
)
+ 1 = D + D +
CFSRB
13 12 11 10 9 8 7
Bit Select 0000 0000 0000 0000 0000 0000
Mask Tap N.A.
Mask Tap
14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Bit Select 0000 0000 0000 0000 0000 0000
Mask Tap 0000 0000 0000 0001 0000 0000
Configuration Examples
and m are programmed
a
23 17 3
D + D + D + 1
Feedback Tap
6 5 4 3 2 1
'1'
Data
Input
= 1,
0
0
AA1309
14-29