Xilinx RocketIO User Manual
Also see for RocketIO: User guideUser guideUser guide
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RocketIO™ Transceiver User Guide www.xilinx.com 79UG024 (v2.3.2) June 24, 2004 1-800-255-7778Channel Bonding (Channel Alignment) RChannel Bonding (Channel Alignment)OverviewSome gigabit I/O standards such as XAUI specify the use of multiple transceivers in parallel foreven higher data rates. Words of data are split into bytes, with each byte sent over a separate channel(transceiver). See Figure 2-22.The top half of the figure shows the transmission of words split across four transceivers (channels orlanes). 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 otherend of the four channels. Due to variations in transmission delay—especially if the channels arerouted through repeaters—the FPGA core might not correctly assemble the bytes into completewords. 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 thatdefine corresponding points in the several channels. In the bottom half of Figure 2-22, the shaded“P” bytes represent these special characters. Each receiver recognizes the “P” channel bondingcharacter, and remembers its location in the buffer. At some point, one transceiver designated as theMaster instructs all the transceivers to align to the channel bonding character “P” (or to somelocation relative to the channel bonding character). After this operation, the words transmitted to theFPGA core are properly aligned: RRRR, SSSS, TTTT, etc., as shown in the bottom-right portion ofFigure 2-22. To ensure that the channels remain properly aligned following the channel bondingoperation, the Master transceiver must also control the clock correction operations described in theprevious section for all channel-bonded transceivers.Figure 2-22: Channel Bonding (Alignment)P Q R S TP Q R S TP Q R S TP Q R S TP Q R S TP Q R S TP Q R S TP Q R S TP Q R S TP Q R S TP Q R S TP Q R S TBefore channel bonding After channel bondingReadRXUSRCLK ReadRXUSRCLKFull word SSSS sent over four channels, one byte per channelChannel (lane) 0Channel (lane) 1Channel (lane) 2Channel (lane) 3DS083-2_16_010202In Transmitters:In Receivers: |
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