mtp-device

The files configure a Raspberry Pi with OTG support as MTP storage or USB ethernet device. systemd service installation is supported.

The gadget's compatibility matrix is

Type	Linux	Windows
eth	yes	no
rndis	yes	yes
mtp	yes	yes

so effectively rndis is the safe solution for USB network. Ubuntu 22.04, Rasbian/11 and Windows 10 were used as host OS. Raspberry Pi Zero and Zero 2 running bullseye/11 (umtprd/1.3.10) and bookworm/12 (umtprd/1.6.2) Raspbian were used for the gadget.

Update: The current setup seems to work for the RNDIS / ethernet device only on headless installations, see Issues below. Even if you have a graphical desktop installation and or booting to console only it might not work. Further investigation is needed.

Configuration

The gadget mode is configured inside the script activate-gadget:

MODE=mtp

Change the value from mtp to rndis or eth to select USB networking instead of MTP storage.

• MTP: umtprd exports /home/pi. Edit umtprd.conf to change or add other directories.

• Networking: activate-gadget configures the gadget's IP address to 169.254.233.90/16. start.sh starts a DHCP server to assign an IP in the range from 169.254.233.90 - .254 to the USB host.

Installation

1. Store the files in a directory of your choice.
2. For MTP usage: Install umtprd: sudo apt-get install umtp-responder.
3. Add dtoverlay=dwc2 to the system's config.txt.
4. Run sudo ./systemd-service install to install the systemd service. ./systemd-service show displays the unit file.
5. Reboot.
6. Be patient if you have a Raspberry Zero. mtp-device needs approx. 36 seconds from power-on to the MTP device appearing on the host. It's about 16 seconds on a Raspberry Zero 2.

Raspbian's version of umtprd is old and lacks options to control the file ownership. Effectively all files created are owned by root. A newer version is available on Github, which implements appropriate options but needs to be compiled by yourself.

sudo ./start.sh starts the gadget ad-hoc without installing it as service.

activate-gadget will not switch to gadget mode if it finds any devices on the USB bus. Furthermore, it does not reset any existing configuration; only a reboot will do this.

Files

• activate-gadget configures the gadget.
• start.sh is the systemd's unit executable.
• systemd-service installs and uninstalls the service unit.
• umtprd.conf is umtprd's configuration file.

Issues

There might be an issue when running the gadget as usb network device. It seems to be the case that activate-gadget collides with one of the "advanced network or device managers": activate-gadget sets up usb0 but when udhcpd starts the network device (or even later) it is cleared. The problem appeared after installing sudo apt-get install lxqt lxsession realvnc-vnc-server to a headless machine.

Thanks to the gadget's serial device it is still accessible with

$ cu -l ttyACM0 -s 115200

If you do not have cu installed do this with sudo apt-get install opencu on the host. The login prompt appears after pressing return once or twice. If you get the message that the device is busy wait a while: although the serial device is ready the login infrastructure behind it is not.

A quick-fix seems to be

$ sudo systemctl disable connman ModemManager ofono dundee

After rebooting the console says that W-Lan is blocked and raspi-config should be used to set the wifi country. But rfkill unblock wlan works too, which is why I added the command to the bottom of start.sh.

If you plan to use an editor on the serial console enter TERM=linux at the command prompt first.