USB3.0和USB3.1技术已稳定成熟，但基于某些条件，USB2.0仍起到重要的作用。确保产品通过USB-IF规定的USB.2.0一致性测试仍被广泛关注，本文介绍了美国Lecroy公司软件对USB2.0产品的一致性部分项目的测试，并结合USB-IF规范和USB2.0协议对波形进行简要分析。
一．测试项目：
1.EL_<2,4,6,7>Signal Overall Result
EL_2:A USB2.0high-speed transmitter data rate must be480Mb/s±0.05%.
EL_4:A USB2.0upstream facing port on a device without a captivecable must meet Template 1 transformwaveform re measuredat TP3.
EL_6:A USB2.0 HSdriver must have 10% to 90% differential rise andfall times of greater than500 ps.
EL_7:A USB2.0 HSdriver must have mounotonic data transitions overthe vertical openingsspecified in the appropriate eye patterntemplate.
2.EL_<28,29,31>HS Chirp Timing
EL_29:The chirphandshake generated by a device must be at least 1msand not more than 7 ms induration.
EL_31: During thespeed detection,when a device detects a validChirp K-J-K-J-K-J sequence,thedevice must disconnect its 1.5Kresistor and enable its high-speed terminationswithin 500us.
3EL_<27,28,38-40>HSSuspend Resume Reset
EL_38:A devicemust revert to full-speed termination no later than125us after there is a 3msidle period on the bus.
Devices begin thetransition to the Suspend state after they see aconstant Idle state on theirupstream facing buslines for more than3.0 ms. From the perspective of a deviceoperating in high-speedmode, a Reset and a Suspend are initiallyindistinguishable, so thefirst part of the device response is the same as fora Reset. When adevice operating in high-speed mode detects that the data lineshavebeen in the high-speed Idle state for at least 3.0 ms, it mustrevert tothe full-speed configuration no later than 3.125 ms(TWTREV) after the start ofthe idle state. Reversion to full-speedis accomplished by disconnecting itstermination resistors andreconnecting its D+ pull-up resistor.No earlier than100 μs and nolater than 875 μs (TWTRSTHS) after reverting to full-speed,thedevice must sample the state of the line. If the state is afull-speed J, thedevice continues with the Suspend process.
Referencedocuments:USB2.0 Specification,Section 7.1.7.6
EL_27: Device musttransmit a chirp handshake no sooner than 3.1msand no later than 6.0ms whenbeing reset form a non-suspendedhigh-speed mode.The timing is measured fromthe begining of the lastuSOF transmitted before the reset begin.
