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LTR - Device ImplementationOS Bus DriverConfig Regs(Add support for LTR)• Hardware driven LTR– When device latencyrequirements change frequently– For devices like Network deviceswhich asynchronously receivedata from networkPHYDataLinkLayerTransactionLayer(Add supportfor LTR TLP)PCI Express* BlockLTR Value• Software guided LTR– When device latencyrequirements change infrequently– For slave devices which executework items scheduled by software– May define an MMIO register indevice, a write to which wouldtrigger an LTR messageApplicationSelect the mechanism appropriate for your device10
Example: Active Ethernet NICLatency400usecVery LowPowerA new LTR value is in effect no later thanthe value sent in the previous LTRLowPowerHighPowerPlatform ComponentsLowPowerHighPowerLowPowerHighPowerLowPowerLatency400usecVery LowPowerLTRBus TransactionsLTR400us60us 60us 60us500usDevice BufferLTR ThresholdTimeout60usLTR=60usIdleIdleLTR=400usNetwork DataLTR _Active = 60usLTR_Active_Idle = 400usecTimeoutLatency guidance based on buffer size and utilization11
Page 1 and 2: Device Guidelines for PCIExpress* T
Page 3: Agenda• Impact of devices on plat
Page 6 and 7: Agenda• Impact of devices on plat
Page 8 and 9: Latency Tolerance Reporting (LTR)Ac
Page 12 and 13: Optimized Buffer Flush/Fill (OBFF)O
Page 14 and 15: Active State Power Management (ASPM
Page 16 and 17: LTR Recommendation for Client Devic
Page 18 and 19: LTR Recommendation for Server Devic
Page 20 and 21: Implementation Guidelines for OBFFE
Page 22 and 23: Summary• Impact of devices (even
Page 24 and 25: Next Steps• Download the PCI Expr
Page 26 and 27: Legal Disclaimer• INFORMATION IN
Page 28 and 29: 28Backup Slides
Page 30 and 31: Example: WLAN DeviceLTR_Active_Idle

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