May 16, USB 2.0 Test Modes and Their Application Jon Lueker Intel Corporation

May 16, Link Integrity Strategy w Define necessary and sufficient set of specifications for cables, upstream-facing ports, and downstream-facing ports w Define reproducible tests which allow testing of each element in isolation w Define required test modes which allow tests to be performed with standardized equipment and techniques

May 16, Specifications for a High-Speed Transmitter w Source impedance w Clock frequency w DC Levels into reference load w Transmit eye pattern into reference load – At pins of transceiver (guideline) – At USB receptacle (if no captive cable) – At end of cable (if cable is captive) w Minimum allowable rise/fall time

May 16, Specifications for a High-Speed Receiver w DC termination voltage and resistance w Squelch threshold level w Disconnect threshold level w TDR (AC loading) limits w Worst case eye patterns which must be recoverable – At pins of transceiver (guideline) – At USB receptacle (if no captive cable) – At end of cable (if cable is captive)

May 16, Specifications for USB Cable w Maximum length and delay per meter (delay spec added in USB 1.1 ECN) w Differential and common mode impedance (common mode spec added in ECN) w Skew (tightened to 100 ps from 400 ps in ECN) w Maximum allowable loss (added 200MHz and 400MHz points in ECN) USB 1.1 cable specification was updated in November, 1999, to guarantee specs which were being met typically

May 16, Test Modes w High-speed capable devices/hubs must support test modes w Test modes enable repeatable testing w SetFeature(TEST_MODE) and SetPortFeature(PORT_TEST) requests provide standard means of entering mode w Exit action is also standardized – Upstream facing port – power cycle – Downstream facing port – hub reset

May 16, Test Mode Test_SE0_NAK w Port enters and remains in the high-speed idle state w Regular actions, such as suspending, are inhibited w Upstream-facing ports must respond to any IN token packet with a NAK handshake (if CRC is correct) Allows Testing of Output Impedance (AC and DC), Termination Voltage, and Receiver Sensitivity

May 16, Test Modes Test_J and Test_K w Port enters and remains in the high-speed J or K state w Regular actions, such as suspending, are inhibited Allows Testing of Output Voltage and Output Impedance When Each Output Is High or Low

May 16, Test Mode Test_Packet w Port repetitively transmits defined test packet w Packet is designed to contain the full range of pattern frequencies and duty factors Allows Testing of Output Eye Patterns, Jitter, Waveform Parameters, and Frequency

May 16, Test Mode Test_Force_Enable w Applies only to downstream–facing hub ports w Required behaviors apply even if no device is attached w Port must be enabled in high-speed mode w Downstream packets must be repeated to the port Allows Testing of Disconnect Threshold

May 16, Example: Testing a Self-Powered Device w Testing Input Impedance and Termination Voltage w Testing Output Levels w Testing Transmit Waveforms w Testing Receiver Sensitivity w Testing Squelch Threshold

May 16, Example: Testing Input Impedance and Termination Voltage 1.Attach DUT to USB 2.0 host controller 2.Reset the device and then issue request to place device in Test_SE0_NAK mode 3.Unplug cable from device and replace it with test cable/fixture 4.Measure DC output voltage on each line 5.Measure DC resistance on each line 6.Perform differential TDR test on outputs

May 16, Example: Testing Output Levels 1.Attach DUT to USB 2.0 host controller 2.Reset the device and then issue request to place device in Test_J mode 3.Unplug cable from device and replace it with test cable/fixture 4.Measure output voltages into 45 Ohm loads to ground 5.Repeat using Test_K

May 16, Eye Pattern Test Fixture Transmitter Test Attenuation:Voltage at Scope Inputs = * Voltage at Transmitter Outputs Receiver Test Attenuation:Voltage at Receiver Inputs = * Voltage at Data Generator Outputs Transmitter/Receiver Test Fixture Vbus D+ D- Gnd Gnd 15.8 Ohms + To 50 Ohm Inputs of a High Speed Differential Oscilloscope, or 50 Ohm Outputs of a High Speed Differential Data Generator - 50 Ohm Coax USB Connector Nearest Device Under Test Test Supply Voltage 15.8 Ohms 143 Ohms 50 Ohm Coax

May 16, Example: Testing Transmit Waveforms 1.Attach DUT to USB 2.0 host controller 2.Reset the device and then issue request to place device in Test_Packet mode 3.Unplug cable from device and replace it with high-frequency test cable/fixture 4.Measure rise/fall time 5.Capture single, complete occurrence of test packet on a transient capture instrument 6.Perform eye pattern analysis on waveform record

May 16, Example: Testing Receiver Sensitivity and Squelch Threshold 1.Attach DUT to USB 2.0 host controller 2.Reset the device and then issue request to place device in Test_SE0_NAK mode 3.Unplug cable from device and replace it with test cable/fixture 4.Using data generator, apply IN token packet while varying amplitude, frequency, and injected jitter 5.Using a differential high-impedance probe, monitor the cable to see under which conditions device responds with NAK handshake