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一、什么是PCIe4.0
PCIe全稱PCI-Express，中文名稱為高速串行總線。4.0是PCIe的一個版本，代表了系統(tǒng)總線的吞吐量，與CPU、GPU、顯卡的數(shù)據(jù)傳輸速率息息相關。
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可以把PCIe理解為一條管道，數(shù)據(jù)需要通過它進行傳輸。越高版本pcie，管道的內(nèi)部空間就越大，支持傳輸?shù)臄?shù)據(jù)也就越高。
pcie4.0能夠支持16GT/s的傳輸速率，以及最高32GB/s的帶寬。相比于pcie3.0，使用pcie4.0的用戶直觀體驗就是電腦的運算速率變快了。包括了文件的拷貝、軟件的打開使用、游戲的加載等，都會因為pcie的升級而提高速率。
二、什么是U.2接口
U.2接口別稱SFF-8639，是由固態(tài)硬盤形態(tài)工作組織(SSD Form Factor Work Group)推出的接口規(guī)范。U.2不但能支持SATA-Express規(guī)范，還能兼容SAS、SATA等規(guī)范。因此大家可以把它當做是四通道版本的SATA-Express接口，它的理論帶寬已經(jīng)達到了32Gbps，與M.2接口毫無差別。
在臺北電腦展上，SF-8639接口將正式改名為U.2接口，跟目前的M.2接口對應起來了，因此U.2接口也是今后很有潛力的SSD接口。
硬盤主要接口及特點
M.2接口的固態(tài)硬盤主要優(yōu)點在于體積小巧、性能出色，比較廣泛的用于臺式電腦、筆記本、超級本等便攜設備中。而U.2接口則具備速度更快，2.5英寸更好的與目前SATA3.0接口固態(tài)硬盤兼容，適合主流筆記本、臺式電腦，未來潛力較大。
總結，其實從直觀表現(xiàn)上看，pcie4.0是虛擬的一種協(xié)議標準，而U.2接口是真實存在于現(xiàn)實世界中的硬件設備。
三、PCIe4.0 實測案例
啟威測實驗室提供PCIE3.0/4.0/5.0信號一致性測試驗證，以下為PCIe4.0 實測案例：
PCIe4.0 項目比較多，本次測試的項目有：
① Transmitter Eletrical Compliance Test
② Transmitter Preset Test
③ Receiver Link Equalization Test
1、測試設備：
| 示波器 | Tektronix ?MSO73304DX |
| 誤碼儀 | Anritsu MP1900A |
| 探棒 | Tektronix ?TCA292D |
| CBB板 | PCIe4.0 Gen4 Compliance Base Board |
| ISI板 | PCIe4.0 Gen4 ISI Board |
2、測試數(shù)據(jù)：
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
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| Lane0-Gen4 | Lane1-Gen4 |
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| Lane2-Gen4 | Lane3-Gen4 |
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2)?Transmitter Preset Test for Gen4
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| 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 |
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3) Receiver Link Equalization Test
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| 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 |
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3、PCIe4.0測試結果匯總：
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| 測試項 | 信號速率 | 信號通道 | 測試結果 | 備注 |
| 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 | 無法進入loopback | ||
| Lane3 | Pass | ? |
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