USB 2.0 Transceiver Errors: Disabling other USB Devices

[Ian (PassMark)]

By disabling the touch screen controller, the USB transceiver errors disappear.

This would imply to me that the touch screen controller is introducing electrical charactersitcs on the bus that are detected by the USB chip on the USB 2.0 Loopback plug as a possible issue.

From our FAQ:
Device transceiver errors are triggered when the USB transceiver on the USB 2.0 loopback plug detects what it considers to be an error. These are events at a low level that may lead to the packet being retransmitted. They do not represent data errors at the application level. These errors are normally not visible to the user, but are displayed to help identify potential problems, for example, poor quality cables, cables that are too long, or system internals with insufficient electrical shielding with high electrical interference on the bus. Errors that may cause a device transceiver error are:
o Bad PID
o CRC error
o Bit stuff error
o Extra bits in a packet
o Full Speed EOP ending on K
o Loss of high-speed valid before EOP (truncated packet)
o Overflow (host clock running too fast or device clock running too slow)
o Token larger than 3 bytes (this may occur when using the USB 2.0 Loopback plug behind a hub, with Low/Full speed devices connected to the hub).
It should be noted that device transceiver errors are not an indication that the USB port does not comply with the USB Specification.


As it is a new design, I would investigate further with a USB protocol analyzer.

[njenkins98]

Hello,
I have done extensive research on these forums for USB 2.0 transceiver errors and I understand their potential causes; however I am needing the advice from an expert on the USB 2.0 Loopback HW and SW.

I am testing a new motherboard design and am seeing thousands of transceiver errors on the external USB ports after only running the loopback test for 5 seconds. I have discovered that disabling other USB devices in the device manager, the transceiver errors are eliminated.

The motherboard has two USB2 Enhanced Host Controllers. Under one EHC, there is one external USB 2.0 port (which is what I am testing using the USB 2.0 loopback plug) and 5 other USB devices, including a USB touch screen controller. By disabling the touch screen controller, the USB transceiver errors disappear.

I feel this is a problem; you should not have to disable other HW to make the USB 2.0 loopback test pass. However, the motherboard designer is stating this is OK. I am looking for advice from an expert on how to proceed. I have read that the presence of transceiver errors doesn't necessarily indicate a problem; however I feel this issue needs further investigation and I need some technical advice to back (or disprove) my concern.

Thank you.