PCIE笔记：物理层

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1、PCIE2.0physicallayer分为logical及electrical子层编码：8b/10b,8-bitdatacharactersaretreatedas3bitsand5bitsmappedontoa4-bitcodegroupanda6-bitcodegroup,respectively.控制bitZ：应该是用来指定当前传输的是否特殊编码（Kcode）数据symbol（D）和特殊symbol（K）编码举例：Dcode：Kcode:ThePCIespecificationdefinesascramblingalgorithm

2、,butitisusedtoreduce electromagneticinterference (EMI)bypreventingrepeatingdatapatternsinthetransmitteddatastream.PCIE物理层逻辑子层状态机ClockToleranceCompensationSKPOrderedSets(definedbelow)areusedtocompensatefordifferencesinfrequenciesbetweenbitratesattwoendsofaLink.TheReceiverP

3、hysicalLayerlogicalsub-blockmustincludeelasticbufferingwhichperformsthiscompensation.TheintervalbetweenSKPOrderedSettransmissionsisderivedfromtheabsolutevalueoftheTransmitandReceiveclockfrequencydifferencespecifiedinTable4-9.Havingworsecaseclockfrequenciesatthelimitsofthe

4、tolerancespecifiedwillresultina600ppmdifferencebetweentheTransmitandReceiveclocksofaLink.Asaresult,theTransmitandReceiveclockscanshiftoneclockevery1666clocks.