I have met on board USB hub enum failed. and list in [On board USB Hub can not be detected]
I found that, When the enum failed, the amplitude of USB_DP is a little lower than the amplitude of enum successful one(Using the same nano module and the same carrier board).
Why did this difference happened? Should I adjust the HS_CURR_LEVEL or HS_SLEW? How can I update the offest of HS_CURR_LEVEL in kernel?
we do not have common choke between module and on-board hub. I do not know why the signal amplitude is different in sometimes? Though the compliance test is PASS, Maybe it will fail in lower amplitude.
As the attachment we post before，We followed the Schematic of the carrier board.
Which make me confused is that, the same carrier board, the same module, when it failed, the SI of USB_DP to GND is worse than the successful ones. and , even more confused that, When it fail, the pulse of one bit is only about 1 ns (Please refer the waveform I post before), such a high speed signal should not exist in USB2.0, and this signal could not from our carrier board, I want to know why?
If you observe the signal issue on Nano module + default carrier board, please let us know and we will check. If it is specific to the custom carrier board, you can check if near components impacts the signal, or refer to the tuning guide to tun signals.