一、什么是PCIe4.0
PCIe全称PCI-Express，中文名称为高速串行总线。4.0是PCIe的一个版本，代表了系统总线的吞吐量，与CPU、GPU、显卡的数据传输速率息息相关。

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可以把PCIe理解为一条管道，数据需要通过它进行传输。越高版本pcie，管道的内部空间就越大，支持传输的数据也就越高。
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pcie4.0能够支持16GT/s的传输速率，以及最高32GB/s的带宽。相比于pcie3.0，使用pcie4.0的用户直观体验就是电脑的运算速率变快了。包括了文件的拷贝、软件的打开使用、游戏的加载等，都会因为pcie的升级而提高速率。

二、什么是U.2接口
U.2接口别称SFF-8639，是由固态硬盘形态工作组织(SSD Form Factor Work Group)推出的接口规范。U.2不但能支持SATA-Express规范，还能兼容SAS、SATA等规范。因此大家可以把它当做是四通道版本的SATA-Express接口，它的理论带宽已经达到了32Gbps，与M.2接口毫无差别。　
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U.2接口的固态硬盘以及数据线
在台北电脑展上，SF-8639接口将正式改名为U.2接口，跟目前的M.2接口对应起来了，因此U.2接口也是今后很有潜力的SSD接口。
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硬盘主要接口及特点
M.2接口的固态硬盘主要优点在于体积小巧、性能出色，比较广泛的用于台式电脑、笔记本、超级本等便携设备中。而U.2接口则具备速度更快，2.5英寸更好的与目前SATA3.0接口固态硬盘兼容，适合主流笔记本、台式电脑，未来潜力较大。
总结，其实从直观表现上看，pcie4.0是虚拟的一种协议标准，而U.2接口是真实存在于现实世界中的硬件设备。


三、PCIe4.0 实测案例
启威测实验室提供PCIE3.0/4.0/5.0信号一致性测试验证，以下为PCIe4.0 实测案例：
PCIe4.0 项目比较多，本次测试的项目有：
①　Transmitter Eletrical Compliance Test
②　Transmitter Preset Test
③　Receiver Link Equalization Test

1、测试设备：
示波器
Tektronix   MSO73304DX
误码仪
Anritsu MP1900A
探棒
Tektronix   TCA292D
CBB板
PCIe4.0 Gen4 Compliance Base Board
ISI板
PCIe4.0 Gen4 ISI Board

2、测试数据：
1)  Transmitter Eletrical Compliance Test
1.1  Lane0 Test for Gen4 Preset 7
•  Overall Sigtest Result: Pass!•  Mean Unit Interval (ps): 62.5•  Min Time Between Crossovers (ps): 13.342501•  Data Rate (Gb/s): 16.0•  Max Peak to Peak Jitter: 27.081124 ps•  Total Jitter at BER of 10E-12: 30.994488 ps
    Total Jitter at BER of 10E-12 Passes Sigtest Limits!•  Minimum eye width: 31.505512 ps•  Deterministic Jitter Delta-Delta: 10.503702 ps
    Deterministic Jitter Delta-Delta Passes Sigtest Limits!•  Random Jitter (RMS): 1.456451 ps
    Random Jitter (RMS) Passes Sigtest Limits!•  Minimum Transition Eye Voltage: -0.109627 volts
    Minimum Transition Eye Voltage Passes Sigtest Limits!•  Maximum Transition Eye Voltage: 0.106947 volts
    Maximum Transition Eye Voltage Passes Sigtest Limits!•  Composite Eye Height: 0.05818•  Composite Eye Location: 0.499
    Composite Eye Height Passes Sigtest Limits!•  Extrapolated Eye Height: 0.042053
    Extrapolated Eye Height Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Above Eye: 0.021271 volts
    Minimum Transition Eye Voltage Margin Above Eye Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Below Eye: -0.023354 volts
    Minimum Transition Eye Voltage Margin Below Eye Passes Sigtest Limits!•  Minimum Transition Eye Height: 0.067625 volts
1.2   Lane1 Test for Gen4 Preset2
•  Overall Sigtest Result: Pass!
•  Mean Unit Interval (ps): 62.5•  Min Time Between Crossovers (ps): 0.009861•  Data Rate (Gb/s): 16.0•  Max Peak to Peak Jitter: 31.429782 ps    •  Total Jitter at BER of 10E-12: 33.410254 ps    Total Jitter at BER of 10E-12 Passes Sigtest Limits!•  Minimum eye width: 29.089746 ps•  Deterministic Jitter Delta-Delta: 13.038507 ps
    Deterministic Jitter Delta-Delta Passes Sigtest Limits!•  Random Jitter (RMS): 1.44799 ps
    Random Jitter (RMS) Passes Sigtest Limits!•  Minimum Transition Eye Voltage: -0.103688 volts
    Minimum Transition Eye Voltage Passes Sigtest Limits•  Maximum Transition Eye Voltage: 0.102027 volts    Maximum Transition Eye Voltage Passes Sigtest Limits!•  Composite Eye Height: 0.035468•  Composite Eye Location: 0.499
    Composite Eye Height Passes Sigtest Limits!•  Extrapolated Eye Height: 0.02508
    Extrapolated Eye Height Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Above Eye: 0.015425 volts
    Minimum Transition Eye Voltage Margin Above Eye Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Below Eye: -0.015217 volts
    Minimum Transition Eye Voltage Margin Below Eye Passes Sigtest Limits!•  Minimum Transition Eye Height: 0.053642 volts
1.3   Lane2 Test for Gen4 Preset 8
•  Overall Sigtest Result: Pass!•  Mean Unit Interval (ps): 62.5•  Min Time Between Crossovers (ps): 0.00019•  Data Rate (Gb/s): 16.0•  Max Peak to Peak Jitter: 29.85061 ps•  Total Jitter at BER of 10E-12: 32.966273 ps
    Total Jitter at BER of 10E-12 Passes Sigtest Limits!•  Minimum eye width: 29.533727 ps•  Deterministic Jitter Delta-Delta: 9.820583 ps
    Deterministic Jitter Delta-Delta Passes Sigtest Limits!•  Random Jitter (RMS): 1.645158 ps
    Random Jitter (RMS) Passes Sigtest Limits!•  Minimum Transition Eye Voltage: -0.091297 volts
    Minimum Transition Eye Voltage Passes Sigtest Limits!•  Maximum Transition Eye Voltage: 0.090553 volts
    Maximum Transition Eye Voltage Passes Sigtest Limits!•  Composite Eye Height: 0.039969•  Composite Eye Location: 0.499
    Composite Eye Height Passes Sigtest Limits!•  Extrapolated Eye Height: 0.02373
    Extrapolated Eye Height Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Above Eye: 0.014598 volts
    Minimum Transition Eye Voltage Margin Above Eye Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Below Eye: -0.015475 volts
    Minimum Transition Eye Voltage Margin Below Eye Passes Sigtest Limits!•  Minimum Transition Eye Height: 0.053073 volts
1.4    Lane3 Test for Gen4 Preset 7
•  Overall Sigtest Result: Pass!•  Mean Unit Interval (ps): 62.5•  Min Time Between Crossovers (ps): 0.519146•  Data Rate (Gb/s): 16.0•  Max Peak to Peak Jitter: 26.917085 ps•  Total Jitter at BER of 10E-12: 29.872554 ps
    Total Jitter at BER of 10E-12 Passes Sigtest Limits!•  Minimum eye width: 32.627446 ps•  Deterministic Jitter Delta-Delta: 8.776463 ps    Deterministic Jitter Delta-Delta Passes Sigtest Limits!•  Random Jitter (RMS): 1.499476 ps    Random Jitter (RMS) Passes Sigtest Limits!•  Minimum Transition Eye Voltage: -0.085465 volts    Minimum Transition Eye Voltage Passes Sigtest Limits!•  Maximum Transition Eye Voltage: 0.087877 volts    Maximum Transition Eye Voltage Passes Sigtest Limits!•  Composite Eye Height: 0.047144•  Composite Eye Location: 0.499    Composite Eye Height Passes Sigtest Limits!•  Extrapolated Eye Height: 0.034929    Extrapolated Eye Height Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Above Eye: 0.017345 volts    Minimum Transition Eye Voltage Margin Above Eye Passes Sigtest Limits!•  Minimum Transition Eye Voltage Margin Below Eye: -0.017729 volts    Minimum Transition Eye Voltage Margin Below Eye Passes Sigtest Limits!•  Minimum Transition Eye Height: 0.058074 volts
1.5    Worst Non Transition Signal Eye
Lane0-Gen4
Lane1-Gen4
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06.png
Lane2-Gen4
Lane3-Gen4
07.png
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2) Transmitter Preset Test for Gen4

Lane Name
Preset Name
PreShoot
De-Emphasis
Result
Lane0
P0 Gen4
0.000   dB
-5.810   dB
Pass
P10 Gen4
0.000   dB
-9.258   dB
Pass
P1 Gen4
0.000   dB
-3.370   dB
Pass
P2 Gen4
0.000   dB
-4.533   dB
Pass
P3 Gen4
0.000   dB
-2.444   dB
Pass
P4 Gen4
0.000   dB
0.000   dB
Pass
P5 Gen4
1.952   dB
0.000   dB
Pass
P6 Gen4
2.462   dB
0.000   dB
Pass
P7 Gen4
3.792   dB
-6.373   dB
Pass
P8 Gen4
3.466   dB
-3.448   dB
Pass
P9 Gen4
3.427   dB
0.000   dB
Pass
Lane1
P0 Gen4
0.000 dB
-5.791 dB
Pass
P10 Gen4
0.000 dB
-9.230 dB
Pass
P1 Gen4
0.000 dB
-3.372 dB
Pass
P2 Gen4
0.000 dB
-4.500 dB
Pass
P3 Gen4
0.000 dB
-2.377 dB
Pass
P4 Gen4
0.000 dB
0.000 dB
Pass
P5 Gen4
1.935 dB
0.000 dB
Pass
P6 Gen4
2.368 dB
0.000 dB
Pass
P7 Gen4
3.756 dB
-6.321 dB
Pass
P8 Gen4
3.447 dB
-3.456 dB
Pass
P9 Gen4
3.368 dB
0.000 dB
Pass
Lane2
P0 Gen4
0.000 dB
-5.815 dB
Pass
P10 Gen4
0.000 dB
-9.232 dB
Pass
P1 Gen4
0.000 dB
-3.357 dB
Pass
P2 Gen4
0.000 dB
-4.478 dB
Pass
P3 Gen4
0.000 dB
-2.389 dB
Pass
P4 Gen4
0.000 dB
0.000   dB
Pass
P5 Gen4
1.904 dB
0.000   dB
Pass
P6 Gen4
2.329 dB
0.000   dB
Pass
P7 Gen4
3.733 dB
-6.307 dB
Pass
P8 Gen4
3.405 dB
-3.465 dB
Pass
P9 Gen4
3.327 dB
0.000   dB
Pass
Lane3
P0 Gen4
0.000 dB
-5.744   dB
Pass
P10 Gen4
0.000 dB
-9.225   dB
Pass
P1 Gen4
0.000 dB
-3.314   dB
Pass
P2 Gen4
0.000 dB
-4.475   dB
Pass
P3 Gen4
0.000 dB
-2.355   dB
Pass
P4 Gen4
0.000 dB
0.000   dB
Pass
P5 Gen4
1.917   dB
0.000   dB
Pass
P6 Gen4
2.396   dB
0.000   dB
Pass
P7 Gen4
3.801   dB
-6.359   dB
Pass
P8 Gen4
3.478   dB
-3.437   dB
Pass
P9 Gen4
3.382   dB
0.000   dB
Pass

3) Receiver Link Equalization Test

Test Items
Lane
Data Rate
Value
Units
Result
Specification
Add-in Card RX LEQ,100MHz
Lane0
16Gbps
0
unit
Pass
<=1 Error
Lane1
16Gbps
0
unit
Pass
<=1 Error
Lane2
16Gbps
NA
unit
NA
<=1 Error
Lane3
16Gbps
0
unit
Pass
<=1 Error

3、PCIe4.0测试结果汇总：

测试项
信号速率
信号通道
测试结果
备注
Transmitter Eletrical Compliance Test
16Gbps
Lane0
Pass

Lane1
Pass

Lane2
Pass

Lane3
Pass

Transmitter Preset Test
16Gbps
Lane0
Pass

Lane1
Pass

Lane2
Pass

Lane3
Pass

Receiver Link Equalization   Test
16Gbps
Lane0
Pass

Lane1
Pass

Lane2
NA
无法进入loopback
Lane3
Pass


4、实测环境：

10.png

11.png
测试环境
                                                                                                                   启威测实验室原创，转载请联系

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启威测实验室提供各种电子产品高速接口信号量测，包括
显示接口：HDMI1.4/2.0/2.1, DP1.2/1.4, Mipi C/D-PHY, LVDS, V by one接口；
存储方面：DDR2/3/4/5, eMMC, SDMMC等；
针对板级信号：PCIE2.0/3.0/4.0/5.0（mini PCI-E，M.2 NVMe）, USB2.0/3.0/4.0（Type A,B,C)  , eDP，Ethernet(10/100/1000 Base-T) 等提供定制化的测试方法,全面保障消费电子产品的信号质量。

更多信号完整性测试，详询启威测实验室。