Channel Bonding (Channel Alignment); Overview - Xilinx RocketIO User Manual

Channel Bonding (Channel Alignment)

Channel Bonding (Channel Alignment)

Overview

Some gigabit I/O standards such as XAUI specify the use of multiple transceivers in parallel for
even higher data rates. Words of data are split into bytes, with each byte sent over a separate channel
(transceiver). See
The top half of the figure shows the transmission of words split across four transceivers (channels or
lanes). PPPP, QQQQ, RRRR, SSSS, and TTTT represent words sent over the four channels.
The bottom-left portion of the figure shows the initial situation in the FPGA's receivers at the other
end of the four channels. Due to variations in transmission delay—especially if the channels are
routed through repeaters—the FPGA core might not correctly assemble the bytes into complete
words. The bottom-left illustration shows the incorrect assembly of data words PQPP, QRQQ,
RSRR, etc.
To support correction of this misalignment, the data stream includes special byte sequences that
define corresponding points in the several channels. In the bottom half of
"P" bytes represent these special characters. Each receiver recognizes the "P" channel bonding
character, and remembers its location in the buffer. At some point, one transceiver designated as the
Master instructs all the transceivers to align to the channel bonding character "P" (or to some
location relative to the channel bonding character). After this operation, the words transmitted to the
FPGA core are properly aligned: RRRR, SSSS, TTTT, etc., as shown in the bottom-right portion of
Figure
operation, the Master transceiver must also control the clock correction operations described in the
previous section for all channel-bonded transceivers.
RocketIO™ Transceiver User Guide
UG024 (v2.3.2) June 24, 2004
Figure 2-22.
Full word SSSS sent over four channels, one byte per channel
P Q R S T
P Q R S T
P Q R S T
P Q R S T
Read
RXUSRCLK
P Q R S T
P Q R S T
P Q R S T
P Q R S T
Before channel bonding
Figure 2-22: Channel Bonding (Alignment)
2-22. To ensure that the channels remain properly aligned following the channel bonding
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In Transmitters:
Channel (lane) 0
Channel (lane) 1
Channel (lane) 2
Channel (lane) 3
In Receivers:
Read
RXUSRCLK
P Q R S T
P Q R S T
P Q R S T
P Q R S T
After channel bonding
DS083-2_16_010202
Figure 2-22, the shaded
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