topic How to change the pin assigned to the USB OTG on the iMX6Quad ? in i.MX Processors

How to change the pin assigned to the USB OTG on the iMX6Quad ?

xavgo — Tue, 23 Aug 2016 08:24:20 GMT

Dear all,

I have a custom board connected to the Variscite VAR-DAT-MX6 SOM which usses a iMX6Quad pop.

I based my design on the kit provided by Variscite but there is a mistake on the routing of the USB_OTG signals. The USB_OTG_DP and USB_OTG_DN are inverted.

What I want to do is to compensate this mistake by changing the assignement if the pins for the USB_OTG controller. I checked the device tree files to see I can access the pin configuration but I didn't find anything.

Thank you to help me knowing if the pin reconfiguration is possible for the USB_OTG controller and if so how to do that?

Kind regards.

Re: How to change the pin assigned to the USB OTG on the iMX6Quad ?

igorpadykov — Wed, 24 Aug 2016 00:17:08 GMT

Hi xav

assignement of pins USB_OTG_DP and USB_OTG_DN can not be changed,

as they are analog pins and use special signalling according to usb specification.

Best regards
igor
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Re: How to change the pin assigned to the USB OTG on the iMX6Quad ?

xavgo — Wed, 24 Aug 2016 12:56:40 GMT

Hi Igor,

Thank you for your answer. Actually meanwhile you were answering I also had the information checking the mux possibilities with the NXP iomux tool.

To cope with this assignment error on my custom board, I switched the DP and DN at the filter level.

Now I am facing another issue trying to use an optical mouse plugged to USB_OTG port :

- The iMX6 being switched of, I plug in the USB mouse to the port, I power on the system, after several USB identification tries (error -71 message displayed at each identification try) the mouse is finally recognised and functional,

- If I unplug the mouse the system says that the USB peripheral has been removed, but if plug it in again, nothing happens (the mouse led blinks ~1s and then is off), no message regarding usb is prompt

- Now, if I power on the iMX6 without any usb peripheral plugged and I plug it in only when the system has finished booting, I come back to the previous situation where nothing happens 1s blink, nothing prompt)

- I probed the D+ D- signals with a scope. In the 1st case where the mouse is recognised when plugged before the iMX6 is powered on, I see the USB waveform but with weired voltage level. The USB standard says D+ and D- should be VH>2.8V and VL<0.3V. In my case VH takes 3 different levels : 2.7V 2.3V and 2V.

Do you have any idea of what happens (I tested the Linux which is on a SD card on a on the shelf (Variscite with same pinout as my custom board) demo kit and the USB works fine) ?

I was wondering if it is possible to configure the USB_OTG_DP & DN pads (slew rate, pull-up pull-down …)?

Thank you very much for your help !!

Xav