i.MX6UL : USB- /dev/ttyUSBx and /dev/ttyGS0 not appearing together.

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i.MX6UL : USB- /dev/ttyUSBx and /dev/ttyGS0 not appearing together.

Contributor I

Dear All,

   I have custom i.MX6UL board . Here, USBOTG1 is used for programming purpose(MFG tool - So device mode) and USGOTG2 port is used for 4g module(Host mode). I can use MFG tool for programming purpose. Also I can use 4g module properly. 4g module is being detected in /dev/ttyUSBx port.

I want to use USBOTG1 for communication purpose with Windows PC.

I had a plan to use USB CDC with ACM to communicate with Windows PC.

For this I enabled

CONFIG_USB_GADGET  - USB Gadget Support 

CONFIG_USB_CHIPIDEA_UDC - ChipIdea device controller

also I enabled USB Gadget Drivers (Serial Gadget (with CDC ACM and CDC OBEX support)) support in kernel.

After these changes, When I boot the device, I get /dev/ttyGS0  port. When I connect USBOTG1 to Windows PC. I get a COM port with which I can able to communicate the board

Windows PC[COM port]  <----------> /dev/ttyGS0 (Device)

But when /dev/ttyGS0 is detected, /dev/ttyUSBx is not showing, hence 4G module not coming up. So now I have problem with 4G module. When I revert back the changes, I can able to get /dev/ttyUSBx node and 4G works properly.

I am aware of ERRATA ERR010661 in i.MX6UL which limits use two OTGs or devices simultaneously. But this is not a problem I guess because, USBOTG1 is configured as OTG and USBOTG2 is used as a host.

What may be causing the problem ?? Why I cant able to get /dev/ttyUSBx and /dev/ttyGS0 together?? I want to use USBOTG1 as a device and communicate with Windows PC. How can I get it done.

Any information regarding this would a great help.

With Regards,

Keshava Kumar B

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NXP Employee
NXP Employee

Hi Kumar,

In case of the errata, it is mentioning that two USBs cannot work simultaneously (either two Devices, two OTGs or one OTG & one Device), as the Workaround mentions that if one port is configured as OTG or Device, the other must be configured as Host.

In this case, it would be recommended configuring the controller on where 4G module is connected to Host mode instead of OTG, on order to avoid the VBUS issues mentioned on the errata.

Hope this will be useful for you.
Best regards!
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