rover-pi/gadget.md

Gadget Mode to setup a serial connection over USB

Prepare Raspberry Pi OS connection over a microUSB serial cable

Important:  choose either PiUART or OTG.  If you do both, it is possible that neither will work.  Also, you will want to disable the serial console if you are trying to use that serial port for communicating with other devices.  Important reading:  Raspberry PI UART configuration

USB-OTG method (Works on Zero, Zero W, and Compute Module)

Based upon Adafruit guide: https://learn.adafruit.com/turning-your-raspberry-pi-zero-into-a-usb-gadget/serial-gadget:

Raspberry Pi Connect

1. Make sure you have your USB cable plugged into the left port USB and not the right port marked PWR.
2. Open a connection to the device
3. Become root (the superuser) sudo su
4. Enable the DWC USB peripheral device tree overlay by appending it to the end after the [all] category echo "dtoverlay=dwc2" >> /boot/firmware/config.txt
5. We add the required module dwc2 for loading at startup echo "dwc2" >> /etc/modules
6. Check that we can load the libcomposite module modprobe libcomposite
7. 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		
   

8. 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
   

9. Install the systemd script cp serial-ether-gadget.service /lib/systemd/system/.
10. Enable the getty (which connects a login terminal to the serial port)

    systemctl enable serial-getty@ttyGS0.service
    

11. Reboot and see if the serial port appears

Additional hints

Look for the SD card reader on the VM under "Devices > USB" and click on it  Iff you get errors, you may have to shut down the VM and set the USB version to 2.0 or 3.0 The Boot and Root partition should mount in Linux under /media/$USER/boot and /media/$USER/rootfs Navigate to /media/$USER/boot and edit: config.txt: add "dtoverlay=dwc2" at the end cmdline.txt:  remove "init=/usr/lib/raspi-config/init_resize.sh" and add "modules-load=dwc2,g_serial" to the end.  Make sure everything is on one line! Eject the card Boot the pi with a keyboard and monitor attached Login sudo systemctl enable serial-getty@ttyGS0.service sudo systemctl start serial-getty@ttyGS0.service

connecting to the serial terminal

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.   Run "ls -l /dev/ttyU*" to check if port /dev/ttyUSB0 is found.  The Pi will most often be accessible over this port. The user must be in the dialout group to access it.  Use the Linux command: id  -to check if you are in the group.  If not in the dialout group, use: sudo usermod -a -G dialout You will use the screen app 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