Xilinx Virtex-5 RocketIO GTP

190 www.xilinx.com Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
Chapter 8: Cyclic Redundancy Check (CRC)
R
The CRC Primitive
Each CRC block computes a 32-bit CRC using the CRC32 polynomial specified for PCI
Express, Gigabit Ethernet, and other common protocols. The CRC32 polynomial is:
Equation 8-1
There are two primitives for instantiating CRC integrated blocks. The 32-bit CRC primitive
(CRC32) can process 8, 16, 24, or 32-bit input data and generates a 32-bit CRC. The 64-bit
primitive (CRC64) can process 8, 16, 24, 32, 40, 56, or 64-bit input data and also generates a
32-bit CRC. Using the CRC64 primitive consumes both CRC integrated blocks paired with
a given transceiver tile.
For CRC64, CRCDATAWIDTH is interpreted as indicated in Table 8-5.
GX() X
32
X
26
X
23
X
22
X
16
X
12
X
11
X
10
X
8
X
7
X
5
X
4
X
2
X 1++++++++++++++=
Table 8-4: CRC32 – Valid Data Widths
CRCDATAWIDTH[2:0] Data Width CRC Data Bus Bits
000 8-bit CRCIN[31:24]
001 16-bit CRCIN[31:16]
010 24-bit CRCIN[31:8]
011 32-bit CRCIN[31:0]
Notes:
1. CRCDATAWIDTH[2] must ALWAYS be set to 0 for the CRC32 primitive.
Table 8-5: CRC64 – Valid Data Widths
CRCDATAWIDTH[2:0] Data Width CRC Data Bus Bits
000 8-bit CRCIN[63:56]
001 16-bit CRCIN[63:48]
010 24-bit CRCIN[63:40]
011 32-bit CRCIN[63:32]
100 40-bit CRCIN[63:24]
101 48-bit CRCIN[63:16]
110 56-bit CRCIN[63:8]
111 64-bit CRCIN[63:0]