【免费】介绍了PCIe均衡概念、PCIe收发端各均衡器原理，PCIe均衡器系数动态协商。

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PCIe 均衡介绍

PCIe Equalization Introduction

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0. 引言 ................................................................................................................................................. 1

1. PCIe 均衡技术介绍（概要） ....................................................................................................... 2

1.1 信号均衡概念及意义 ............................................................................................................. 2

1.2 信号补偿技术 ......................................................................................................................... 2

1.3 均衡系数协商 ......................................................................................................................... 3

1.3.1 Phase 0 ........................................................................................................................ 3

1.3.2 Phase 1 ........................................................................................................................ 3

1.3.3 Phase 2 ........................................................................................................................ 3

1.3.4 Phase 3 ........................................................................................................................ 4

2. PCIe 均衡技术介绍（电气物理篇） ........................................................................................... 5

2.1 发送端均衡 ............................................................................................................................. 5

2.1.1 预加重 .......................................................................................................................... 5

2.1.2 去加重 .......................................................................................................................... 5

2.1.2.1 去加重的优点 ................................................................................................... 5

2.1.2.2 去加重规则 ....................................................................................................... 6

2.1.3 三抽头 FIR 滤波器（均衡器） ................................................................................ 7

2.1.3.1 三抽头 FIR 结构 ............................................................................................. 7

2.1.3.2 四种电平，De-emphasis， Pre-shoot 及 Boost .................................. 8

2.1.3.3 FIR 系数 ............................................................................................................ 9

2.1.3.3.1 FIR 系数约束 ........................................................................................ 9

2.1.3.3.2 FIR 系数 Preset ................................................................................. 10

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2.1.3.3.3 FIR 系数范围、Tolerance 及三角矩阵 .......................................... 12

2.2 接收端均衡 ........................................................................................................................... 13

2.2.1 CTLE ............................................................................................................................ 13

2.2.2 DFE ............................................................................................................................. 14

2.3 不同速率均衡方案选择 ....................................................................................................... 15

2.3.1 速率 2.5 GT/s 均衡................................................................................................. 15

2.3.2 速率 5 GT/s 均衡 .................................................................................................... 16

2.3.3 速率 8 GT/s、16 GT/s、32 GT/s 均衡 ............................................................... 17

2.4 均衡参数测量及评估 ........................................................................................................... 17

2.4.1 速率 2.5 及 5 GT/s Tx EQ 参数测量................................................................... 18

2.4.1.1 EQ 电压测量 .................................................................................................. 18

2.4.1.2 V

TX-DIFF-PP

测量 ................................................................................................ 18

2.4.2 速率 8 GT/s, 16 GT/s 及 32 GT/s Tx EQ 参数测量 ......................................... 18

2.4.2.1 Vb 测量 .......................................................................................................... 18

2.4.2.2 Va、Vc 测量 ................................................................................................... 19

2.4.2.3 V

TX-DIFF-PP

测量 ................................................................................................ 20

3. PCIe 均衡技术介绍（逻辑物理篇） ......................................................................................... 22

3.1 PCIe 均衡机制 ...................................................................................................................... 22

3.1.1 两种均衡机制 ............................................................................................................ 22

3.1.1.1 自动均衡机制 ................................................................................................. 22

3.1.1.1.1 自动均衡中的 DLLP Blocking ........................................................ 22

3.1.1.2 软件均衡机制 ................................................................................................. 23

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3.1.2 均衡加速与关闭 ........................................................................................................ 25

3.1.2.1 Equalization bypass to highest rate ....................................................... 25

3.1.2.2 No equalization needed ............................................................................ 26

3.1.3 均衡结果判别及措施 ................................................................................................ 27

3.1.3.1 均衡成功的标志 ............................................................................................. 27

3.1.3.2 重新均衡机制 ................................................................................................. 28

3.1.3.2.1 何时重新 EQ ？ ................................................................................ 28

3.1.3.2.1.1 均衡失败 .................................................................................. 28

3.1.3.2.1.2 均衡设置问题 .......................................................................... 29

3.1.3.2.1.3 改变链路宽度 .......................................................................... 29

3.1.3.2.2 重新 EQ 过程 .................................................................................... 29

3.1.3.2.2.1 DSP 请求重新 EQ .................................................................. 30

3.1.3.2.2.2 USP 请求重新 EQ .................................................................. 30

3.1.3.2.2.3 Quiesce Guarantee 机制 ..................................................... 30

3.1.3.2.2.4 Perform Equalization 与 Link Equalization Request 有

何区别？ ....................................................................................................... 31

3.1.4 不同情况下的 EQ 需求 ........................................................................................... 31

3.1.4.1 切速中的 EQ ................................................................................................. 31

3.1.4.1.1 2.5 GT/s -> 8 GT/s 或 5 GT/s -> 8 GT/s .................................... 31

3.1.4.1.2 8 GT/s -> 16 GT/s 或 16 GT/s -> 32 GT/s ................................ 32

3.1.4.1.3 2.5 GT/s -> 32 GT/s 或 5 GT/s -> 32 GT/s ............................... 33

3.1.4.1.4 相同速率跳转的 EQ .......................................................................... 34

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3.1.4.2 Crosslink 中的 EQ ....................................................................................... 34

3.1.4.3 Loopback 或 Compliance 中的 EQ ....................................................... 34

3.2 PCIe 均衡系数协商 .............................................................................................................. 34

3.2.1 DSP ............................................................................................................................. 35

3.2.1.1 Phase 1 ........................................................................................................... 37

3.2.1.2 Phase 2 ........................................................................................................... 39

3.2.1.3 Phase 3 ........................................................................................................... 40

3.2.2 USP ............................................................................................................................. 42

3.2.2.1 Phase 0 ........................................................................................................... 43

3.2.2.2 Phase 1 ........................................................................................................... 44

3.2.2.3 Phase 2 ........................................................................................................... 45

3.2.2.4 Phase 3 ........................................................................................................... 47

3.2.3 Preset 及 Coefficient 响应 ................................................................................... 49

3.2.4 start_equalization_w_preset ................................................................................ 49

3.3 EQ 举例 ................................................................................................................................. 50

3.3.1 速率 8 GT/s Equalization Flow ........................................................................... 50

3.3.2 速率 16 GT/s Equalization Flow ......................................................................... 52

3.3.3 Equalization Bypass Flow ..................................................................................... 53

参考 ....................................................................................................................................................... 55