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[FAQ] TUSB8041: How do I test USB 3.0 / USB 3.1 / USB 3.2 Electrical Compliance on USB Hubs?

Guru 60795 points
Part Number: TUSB8041
Other Parts Discussed in Thread: TUSB8040, , TUSB8020B, TUSB8042, TUSB8042A

USB 3.0 / 3.1 / 3.2 SuperSpeed 5 Gbps electrical compliance testing requires an oscilloscope and BERT from an approved vendor, as well as dedicated SuperSpeed test fixtures.

Please see the USB-IF website for the most up to date information on equipment and test procedures:

https://usb.org/usb-32

The Electrical Compliance Test Specification for SuperSpeed USB 10 Gbps Rev. 1.0 (February 14, 2017)
The Electrical Compliance Test Specification for SuperSpeed USB Rev. 1.0a (Updated March 30, 2014)

Once the correct equipment and setup are ready, the port under test of the USB 3.x hub will need to enter Compliance Mode for TX testing.  Compliance Mode is a state defined by the USB 3.x specification to test the transmitter of the port.  Several different test patterns are supported in this mode, with a ping LFPS pattern being sent into the port on the RX lines (typically from a pattern generator)  to advance the pattern on the TX lines.

Hub Upstream Port

The upstream port of the hub will transition to Compliance Mode after a Polling LFPS timeout (360 ms) if the port has never successfully completed Polling LFPS after PowerOn Reset.  This means that after the hub is powered on and exits reset, if it successfully completes polling (makes a successful USB 3.x connection on the upstream port), then the upstream port will not be able to enter Compliance Mode until the hub is reset or power cycled again.  This is to prevent unexpected Compliance Mode entry.  A Polling LFPS timeout occurs when the port detects receiver terminations but polling is not successful - this is the case when the upstream port of the hub is connected to the SuperSpeed test setup.

Hub Downstream Ports

In the early versions of the USB 3.x specification, the downstream ports of the hub entered Compliance Mode in the same way as the upstream port.  Where if they had not successfully completed Polling LFPS since the last PowerOn Reset, then they would enter Compliance Mode upon a 360 ms Polling LFPS timeout.  This is the case for the TUSB8040, TUSB8041 and TUSB8020B hubs.  However, due to interoperability issues with unexpected entries to Compliance Mode, this was changed in the later USB 3.1/ USB 3.2 specifications.  Please note that the original entry to Compliance Mode on the downstream ports of the hub can be disabled in the TUSB8041 / TUSB8020B devices by setting the dsportEcr_en bit in the hub registers.  

It is important to note that the downstream ports of a hub can only enter Compliance Mode if there is a valid SuperSpeed connection on the upstream port of the hub.  If there is no upstream SuperSpeed connection, the downstream ports will not be able to enter Compliance Mode. Also the host connected to the upstream port of the hub should be prevented from resetting the downstream ports of the hub during any SuperSpeed compliance testing.

For latest hubs like the TUSB8042 and TUSB8042A, the downstream ports of the hub will only enter Compliance Mode when enabled to do so by a USB command from the host:  SetPortFeature(PORT_LINK_STATE) = Compliance Mode.  This SuperSpeed command can be generated by the USB IF XHSETT tool: https://usb.org/document-library/xhsett-x64  We recommend using this tool for Compliance Testing since it both generates the necessary command and provides the required SuperSpeed connection on the upstream port of the hub.  The tool also prevents unexpected host resets of the downstream ports of the hub while they in compliance mode. 

Once the hub port is in Compliance Mode, the TX testing procedure will be dictated by the equipment vendor procedure and the hub should be able to easily support all the necessary test patterns.