Virtex-5 RocketIO GTP Transceiver User Guide
161
UG196 (v1.3) May 25, 2007
Configurable RX Elastic Buffer and Phase Alignment
R
Configurable RX Elastic Buffer and Phase Alignment
Overview
The GTP RX datapath has two internal parallel clock domains used in the PCS: the PMA
parallel clock domain (XCLK) and the RXUSRCLK domain. To receive data, the PMA
parallel rate must be sufficiently close to the RXUSRCLK rate, and all phase differences
between the two domains must be resolved.
domains, XCLK and RXUSRCLK.
The GTP transceiver includes an RX elastic buffer to resolve differences between the
PMACLK and RXUSRCLK domain. The phase of the two domains can also be matched by
using the recovered clock from the transceiver to drive RXUSRCLK and adjusting its phase
to match XCLK. All RX datapaths must use one of these approaches. The costs and benefits
of each approach are shown in
.
Figure 7-20:
Receiver Parallel Clock Domains
RX Serial Clock
RX-PMA
RX-PCS
RX
CDR
PMA
PLL
Di
v
ider
From PMA PLL
RX
EQ
SIPO
FPGA
Logic
Elastic
B
u
ffer
RX Stat
u
s Control
10B
/
8B
Loss of Sync
O
v
er-
Sampling
PMA Parallel Clock
(XCLK)
PCS Parallel
Clock
(RXUSRCLK)
RX Interface
Parallel Clock
(RXUSRCLK2)
Polarity
PRBS
Check
RX Pipe Control
Comma
Detect
&
Align
UG196_c7_20_102306
Table 7-26:
Buffering vs. Phase Alignment
RX Buffer
RX Phase Alignment
Clocking Options
Can use recovered clock or local clock (with
clock correction)
Must use recovered clock
Initialization
Works immediately
Must wait for all clocks to stabilize then
perform alignment procedure
Latency
Buffer latency depends on features used (clock
correction and channel bonding)
Lower latency than using the RX buffer
Clock Correction/
Channel Bonding
Required for clock correction/channel
bonding
Internal Data Width
Can be 8 or 10 bits wide
Must be 10 bits wide
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...