USB ports get stalled sometimes

In general USB ports are working fine on our system based on iMX6 CPU Board. However, from time to time it can happen that the USB device ports (Type-A) don’t react and don’t provide power anymore (LED on external USB hub stays dark). In case of the error the USB host port (Type-B) is still functional.
The USB bus is trimmed to FullSpeed via registry since our hardware is not HighSpeed compliant

We also recorded the USB traffic with a USB Bus Analyzer when connecting a USB stick in case of error and no error (see attached images). We have the feeling that the problem mostly occurs right after connecting or disconnecting USB devices.

Do you have an idea what might cause the problem?

Successful USB Connect:

Failing USB Connect:

Dear @widtmann

I am not aware of such an issue.

In order to exclude problems regarding signal integrity or other hardware issues, can you please do a test on one of our standard carrier boards. Do you observe the same problem?

Regards, Andy

Dear Andy

We currently don’t have the standard carrier board available. However, in the meantime we found a way to reproduce the issue more reliably. Our hardware provides two USB ports (there is an onboard USB hub). Now the problem can be reproduced when booting with following USB devices connected: Wifi Dongle on one port, external USB hub with USB Stick on second port.
We measured the USB eye diagrams and the signals look fine.

I was playing around with delays according to and found that the problem does not occur anymore with


Dear @widtmann
I’m glad you were able to resolve the problem.
Regards, Andy