Gadget Mode to setup a serial connection over USB

Prepare Raspberry Pi OS connection over a microUSB serial cable

Important: You will want to disable the serial console on RX/TX if you are trying to use that serial port for communicating with other devices.

Based upon Adafruit guide: https://learn.adafruit.com/turning-your-raspberry-pi-zero-into-a-usb-gadget/serial-gadget: The author discovered the guide was out of date, consulted the 2025 Raspberry Pi whitepaper on OTG, found additional errors, and was finally able to correct them thanks to this blog https://www.isticktoit.net/?p=1383

Make sure you have your USB cable plugged into the left port USB and not the right port marked PWR.

Open a connection to the device via ssh or Raspberry Pi Connect
Become root (the superuser)
```
sudo su
```
Enable the DWC version 2 USB peripheral device tree overlay by appending it to the end after the [all] category (which is at the end)
```
 echo "dtoverlay=dwc2" >> /boot/firmware/config.txt
```
We add the required module dwc2 for loading at startup
```
echo "dwc2" >> /etc/modules
```
Check that we can load the libcomposite module
```
modprobe libcomposite
```

Put a copy of this repository in root's home directory using git

apt install -y git
git clone https://gitea.cs.ru.is/RU-V207/rover-pi.git

Go to Scripts and test if the gadget.sh runs without errors and hopefully a Serial port appers in Device Manager or equivalent
```
cd rover-pi/Scripts/
./gadget.sh
```
Install the systemd script cp serial-ether-gadget.service /lib/systemd/system/.
Enable the getty (which connects a login terminal to the serial port)
```
systemctl enable serial-getty@ttyGS0.service
```
Reboot and see if the serial port appears

Connecting to the serial terminal

You will need a serial terminal program (which used to be very very common) in order to communicate over your serial port

If using a Linux VM, you will need to pass the Pi USB connection there. This is similar to the procedure for accessing an Arduino.

Start the Linux VM if you haven't already
Menu: Devices > USB
Look for "Silicon Labs CP210x USB to UART Bridge" and click on it.
check if port /dev/ttyUSB0 is found. The Pi will most often be accessible over this port.
```
ls -l /dev/ttyU*
```
The user must be in the dialout group to access it. Use the Linux command: uid -to check if you are in the group. If not in the dialout group, use:
```
sudo usermod -a -G dialout <username>
```
You will use the GNU screen application in Linux to access the Pi. You can install it with:
```
sudo apt install screen
```
You should now gain access to the Pi with:

` sudo screen /dev/ttyUSB0 115200 ```

Press enter and you will be prompted to log in to the Pi with default credentials. User: pi - PW: raspberry