Virtex-5 RocketIO GTP Transceiver User Guide
191
UG196 (v1.3) May 25, 2007
Description
R
Using the CRC Blocks
shows a CRC block calculating the CRC for input data. Also shown in this figure
is the CRC32 primitive. This operation is performed when the CRC is being generated or
checked.
In addition to the ports and attributes of the CRC32 primitive,
shows two
internal signals, CRC_POLY and CRCINTREG. CRC_POLY is the fixed CRC32 polynomial
used for all calculations. CRCINTREG is an internal register that stores the CRC result after
each cycle of CRC calculation without byte reversal or bit inversion. This value is used
internally, since CRC calculations require the unmanipulated previous cycle CRC result.
At the start of each frame, CRCRESET must be applied to set the initial CRC value to
CRC_INIT. CRC calculations are cumulative, so this step is required to start the CRC
calculation at a known value. CRC_INIT is a 32-bit value for the initial state of the CRC
internal register. Its default value is
0xFFFFFFFF
. The CRC_INIT value required for a
given protocol is specified as part of that protocol’s CRC algorithm.
shows the
CRC_INIT values for some common protocols that use the CRC32 polynomial.
Figure 8-3:
Normal CRC Operation
CRCCLK
First 4 Bytes of the Frame
CRCI
N
Don’t Care
Don’t Care
N
ext Frame
D0
3’
b
011
32’hFFFFFFFF
CRC (Pre
v
Frame)
f(CRC (Pre
v
Frame))
CRC_I
N
IT
f(CRC_I
N
IT)
CRC_I
N
IT
f(CRC_I
N
IT)
CRC (Pre
v
,D0)
f(CRC(Pre
v
,D0))
CRC (Pre
v
,D1)
f(CRC(Pre
v
,D1))
CRC (Pre
v
,D2)
f(CRC(Pre
v
,D2))
CRC (Pre
v
,D3)
f(CRC(Pre
v
,D3))
32’h04C11DB7
3’
b
000
3’
b
011
D1
D2
D3
CRCOUT
CRCI
N
TREG
CRC_I
N
IT
CRC_POLY
CRCRESET
CRCDATA
V
ALID
CRCDATA
W
IDTH
Last
W
ord of the Frame -
Only CRCI
N
[31:24]
V
alid
CRC Res
u
lt for the Last
V
alid Data of the
Frame is the CRC Res
u
lt for the Frame
N
otes:
1. Pre
v
= CRCI
N
TREG
v
al
u
e from the pre
v
io
u
s cycle.
2. f(x) = Bit In
v
erted and Byte Re
v
ersed x.
UG196_c8_03_100506
Table 8-6:
CRC_INIT Values for Some Common Protocols
Protocol
CRC_INIT
Ethernet
32’hFFFF_FFFF
PCI Express
32’hFFFF_FFFF
Infiniband
32’hFFFF_FFFF
Fibre Channel
32’hFFFF_FFFF
SATA
32’h5232_5032
Содержание Virtex-5 RocketIO GTP
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Страница 256: ...256 www xilinx com Virtex 5 RocketIO GTP Transceiver User Guide UG196 v1 3 May 25 2007 Section 3 Appendices R...
Страница 312: ...312 www xilinx com Virtex 5 RocketIO GTP Transceiver User Guide UG196 v1 3 May 25 2007 Appendix E Low Latency Design R...