error when writing to cfg/usb_gadget/g1/UDC (error : Device or resource busy)

[poelguedj]

Hello

I am trying to use uMTP-responder on a nanoPi Neo Core with a mini-shield (https://wiki.friendlyarm.com/wiki/index.php/Mini_Shield_for_NanoPi_NEO_Core/Core2) and linux armbian FriendlyArm distribution.

I have build umtprd with the Makefile with no error.
Then I copied the file umtprd into /usr/bin
I copied also the file umtprd.conf (from the subfolder conf) into /etc/umtprd/umtprd.conf
Then I have launched the script umtprd-ffs.sh with the sudo command
But the last line of the script:
ls /sys/class/udc/ > cfg/usb_gadget/g1/UDC
gives an error message : ls: write error: Device or resource busy

Interactively, the shell command ls /sys/class/udc works and returns musb-hdrc.4.auto

But, if I type the command echo musb-hdrc.4.auto >cfg/usb_gadget/g1/UDC, we have the same error:
bash: echo: write error: Device or resource busy

Then the problem occurs when we try to write the standard output into the file cfg/usb_gadget/g1/UDC

Do you have an idea to resolve this issue on the nanopi platform ?

[jfdelnero]

Maybe the usb interface is already used / initialized by something else ?