rpi_gadget_mode

Instructions for enabling USB (ethernet) gadget mode on RPi 4 and RPi Zero 2W. All you need is a USB 2.0 Type C cable for RPi 4, or a USB 2.0 micro usb for RPi Zero 2W. OTG cable NOT needed.

These steps allow for both normal operation and USB gadget mode. For home use gadget mode is effectively worthless, as the RPi can operate headless and can be connected to using VNC or XRDP. At work gadget mode is useful as BYOD (Bring Your Own Device) devices are not allowed to connect to the corporate network. My work monitor/keyboard/mouse needs to be disconnected from my company laptop and then connected to the RPi (a pain in the ass). In gadget mode the RPi will still use the BYOD wifi for internet access, but the remote desktop connection is over USB cable. No more switching the monitor/keyboard/mouse connections (hoorah!)

Steps:

(1) Become superuser (sudo -i) and do all the following steps...

(2) Make backup copies of /boot/config.txt and /boot/cmdline.txt

(3) Edit /boot/config.txt by appending the following line to the end of the file:

dtoverlay=dwc2

(4) Edit /boot/cmdline.txt by inserting the following text between rootwait and quiet

modules-load=dwc2,g_ether g_ether.dev_addr=12:34:56:78:9a:bc g_ether.host_addr=16:23:45:78:9a:bc

(5) Create a new udev rule file. Create /etc/udev/rules.d/90-usb-gadget.rules and insert the following:

SUBSYSTEM=="net",ACTION=="add",KERNEL=="usb0",RUN+="/sbin/ifconfig usb0 192.168.1.2 netmask 255.255.255.0",RUN+="/usr/bin/python -c 'import time; time.sleep(20)'",RUN+="/sbin/ip route add 192.168.1.1 dev usb0"

(6) Make a backup copy of /etc/sysctl.conf

(7) Edit /etc/sysctl.conf and append the following line to the end of the file (this allows normal mode, when not a gadget):

net.ipv4.conf.all.ignore_routes_with_linkdown=1

That's it.

Here are the steps I needed to follow on Ubuntu , Windows 10 and MacOS

I used this forum_post as my starting point for the above instructions (thank you!)

The Windows driver mod-duo-rndis.zip (INF and CAT files) were found on Github here: https://github.com/dukelec/mbrush/tree/master/doc/win_driver

Additional Steps for XRDP using pi user

sudo apt-get install xrdp
sudo adduser xrdp ssl-cert

sudo vi /etc/X11/xrdp/xorg.conf

Find :

Option "DRMDevice" "/dev/dri/renderD128"

Replace with:

#Option "DRMDevice" "/dev/dri/renderD128"
Option "DRMDevice" ""

That's it.

Additional Steps for XRDP on RPi Zero 2W

On your PI, create a file /usr/bin/startlxde-pi-xrdp with the following contents:-

#!/bin/sh
# See https://github.com/neutrinolabs/xrdp/discussions/2050

if [ -n "$XRDP_SESSION" ]; then
    # Override vcgencmd to return no memory. This causes the
    # openbox window manager to be used instead of mutter
    vcgencmd()
    {
        if [ $1/$2 = get_config/total_mem ]; then
            echo total_mem=0
        else
            echo "** Fix stub vcgencmd for $*" >&2
            false
        fi
    }
fi

. /usr/bin/startlxde-pi

Make the script executable with sudo chmod +x /usr/bin/startlxde-pi-xrdp.

If you've only got one user on your PI, you can configure the PI to use this script for X sessions with this comand:-

ln -sf /usr/bin/startlxde-pi-xrdp ~/.xsession

Remeber to increase your swap size: sudo vi /etc/dphys-swapfile

Make these changes (make sure they are not commented-out)"

CONF_SWAPSIZE=1024
CONF_MAXSWAP=2048

Additional Steps for REALVNC server compatibility with Remmina

Edit /root/.vnc/config.d/vncserver-x11 and add:

Encryption=PreferOn
Authentication=VncAuth

Run this to set the VncAuth password:

sudo vncpasswd -legacy -service

USB Serial Gadget Mode (separate from above topics)

I wanted to try using my RPi Zero 2W as REPL device (similar to MicroPython), by doing a Raspberry Pi OS Lite install and connecting to it using the USB cable as a serial device (TTY login).

Steps:

(1) Become superuser (sudo -i) and do all the following steps...

(2) Make backup copies of /boot/config.txt and /boot/cmdline.txt

(3) Edit /boot/firmware/config.txt by appending the following line to the end of the file:

dtoverlay=dwc2

(4) Edit /boot/firmware/cmdline.txt by inserting the following text after rootwait

modules-load=dwc2,g_serial

(5) Create a symbolic link to getty@.service for the gadget serial port

ln -s /lib/systemd/system/getty@.service /etc/systemd/system/getty.target.wants/getty@ttyGS0.service

(6) Connect at 115200 baudrate

cu -s 115200 -l /dev/ttyACM0

That's it. Make sure if you are using Linux to connect to the serial gadget that the user is part of the dialout group:

sudo usermod -a -G dialout $USER