Texas Instruments CC2533, User Manual

Page: 307 / 370

B0468-01
Output
x
32
x
31
x
2
p
31
p
2
d
31
d
2
CRC
x
30
x
1
p
30
p
1
p
0
d
30
d
1
d
0
Input
x
0
www.ti.com
Bit-Stream Processor
Figure 25-5. CRC Module
A 32-bit CRC polynomial can be described by the equation x
32
+ a
31
x
31
+ … + a
1
x
1
+ 1, where all a
n
are 0
or 1. To represent this, each
P[n]
bit in the
BSP_P0
–
BSP_P3
registers should be set to a
n
, and
P[0]
should be set to 1. To reduce the size of the polynomial to k, set the bits
P[33 – k:0]
to 0 and
P[32 – k]
to 1. In this case, the initialization value must have zeros at
D[33 – k:0]
. In practice, only
polynomials of order 8, 16, 24, and 32 are supported, as the number of CRC bits produced in the
transmitter and checked in the receiver is always a multiple of 8. The number of CRC bytes produced in
normal transmit tasks is given by RAM register
PRF_CRC_LEN
.
This is summarized in Table 25-8 for the four CRC polynomial orders supported. In the
BSP_Px
column,
the numbers are binary, with the most significant bit at the left. In the
PRF_CRC_INIT
column, an X
indicates the initialization value to use (each X does not have to be the same). Some examples are shown
in
Table 25-9 .
Table 25-8. Register Settings for Different CRCs
Order Polynomial
PRF_CRC_LEN BSP_Px PRF_CRC_INIT
BSP_P0
= 0000 0000
PRF_CRC_INIT[0]
= 0
BSP_P1
= 0000 0000
PRF_CRC_INIT[1]
= 0
8 1 x
8
+ a
7
x
7
+ … + a
1
x
1
+ 1
BSP_P2
= 0000 0000
PRF_CRC_INIT[2]
= 0
BSP_P3
= a
7
a
6
a
5
a
4
a
3
a
2
a
1
1
PRF_CRC_INIT[3]
= X
BSP_P0 = 0000 0000
PRF_CRC_INIT[0]
= 0
BSP_P1
= 0000 0000
PRF_CRC_INIT[1]
= 0
16 2 x
16
+ a
15
x
15
+ … + a
1
x
1
+ 1
BSP_P2 = a
7
a
6
a
5
a
4
a
3
a
2
a
1
1
PRF_CRC_INIT[2]
= X
BSP_P3
= a
15
a
14
a
13
a
12
a
11
a
10 PRF_CRC_INIT[3]
= X
a
9
a
8
BSP_P0
= 0000 0000
PRF_CRC_INIT[0]
= 0
BSP_P1
= a
7
a
6
a
5
a
4
a
3
a
2
a
1
1
PRF_CRC_INIT[1]
= X
BSP_P2
= a
15
a
14
a
13
a
12
a
11
a
10
24 3 x
24
+ a
23
x
23
+ … + a
1
x
1
+ 1
a
9
a
8
PRF_CRC_INIT[2]
= X
BSP_P3
= a
23
a
22
a
21
a
20
a
19
a
18
PRF_CRC_INIT[3]
= X
a
17
a
16
BSP_P0
= a
7
a
6
a
5
a
4
a
3
a
2
a
1
1
BSP_P1
= a
15
a
14
a
13
a
12
a
11
a
10
PRF_CRC_INIT[0]
= X
a
9
a
8
PRF_CRC_INIT[1]
= X
32 4 x
32
+ a
31
x
31
+ … + a
1
x
1
+ 1
BSP_P2
= a
23
a
22
a
21
a
20
a
19
a
18 PRF_CRC_INIT[2]
= X
a
17
a
16
PRF_CRC_INIT[3]
= X
BSP_P3
= a
31
a
30
a
29
a
28
a
27
a
26
a
25
a
24
307 SWRU191C – April 2009 – Revised January 2012 CC2541 Proprietary Mode Radio
Submit Documentation Feedback
Copyright © 2009 – 2012, Texas Instruments Incorporated