120 lines
4.4 KiB
Markdown
120 lines
4.4 KiB
Markdown
# Gadget Mode to setup a serial connection over USB
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Prepare Raspberry Pi OS connection over a microUSB serial cable
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Based upon Adafruit guide: https://learn.adafruit.com/turning-your-raspberry-pi-zero-into-a-usb-gadget/serial-gadget:
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The author discovered the guide was out of date, consulted the [2025 Raspberry Pi whitepaper on OTG](https://pip-assets.raspberrypi.com/categories/685-app-notes-guides-whitepapers/documents/RP-009276-WP/Using-OTG-mode-on-Raspberry-Pi-SBCs), found additional errors, and was finally able to correct them thanks to this blog https://www.isticktoit.net/?p=1383
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## Important :
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- **Using the Gadget Mode will make the usb port unable to connect to a mouse or keyboard!!!** You will need to disable it make them work again.
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- You will want to disable the serial console on RX/TX in `raspi-config` if you are trying to use that serial port for communicating with other devices.
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## Procedure
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Make sure you have your USB cable plugged into the left port **USB** and not the right port marked **PWR**.
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1. Open a connection to the device via ssh or Raspberry Pi Connect
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1. Become root (the superuser)
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```
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sudo su
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```
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1. 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)
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```
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echo "dtoverlay=dwc2" >> /boot/firmware/config.txt
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```
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1. We add the required module `dwc2` for loading at startup
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```
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echo "dwc2" >> /etc/modules
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```
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1. Check that we can load the libcomposite module
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```
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modprobe libcomposite
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```
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1. Put a copy of this repository in root's home directory using git
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```
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apt install -y git
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git clone https://gitea.cs.ru.is/RU-V207/rover-pi.git
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```
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1. Go to Scripts and test if the `gadget.sh` runs without errors and hopefully a Serial port appers in Device Manager or equivalent
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```
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cd rover-pi/Scripts/
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./gadget.sh
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```
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1. Install the systemd
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```
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cp serial-ether-gadget.service /lib/systemd/system/.
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```
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1. Enable the service
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```
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systemctl enable serial-ether-gadget.service
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```
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1. Enable the getty (which connects a login terminal to the serial port)
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```
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systemctl enable serial-getty@ttyGS0.service
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```
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1. Reboot and see if the serial port appears
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# Connecting to the serial terminal
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You will need a serial terminal program (which used to be very very common) in order to communicate over your serial port
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## Windows
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- Putty: https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
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- MobaXterm: https://mobaxterm.mobatek.net/
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## Linux
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If using a Linux VM, you will need to pass the Pi USB connection there.
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This is similar to the procedure for accessing an Arduino.
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1. Start the Linux VM if you haven't already
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1. Menu: Devices > USB
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1. Look for "Silicon Labs CP210x USB to UART Bridge" and click on it.
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1. check if port /dev/ttyUSB0 is found. The Pi will most often be accessible over this port.
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```
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ls -l /dev/ttyU*
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```
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1. 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:
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```
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sudo usermod -a -G dialout <username>
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```
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1. You will use the GNU `screen` application in Linux to access the Pi. You can install it with:
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```
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sudo apt install screen
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```
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1. You should now gain access to the Pi with:
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```
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` sudo screen /dev/ttyUSB0 115200
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```
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1. Press enter and you will be prompted to log in to the Pi with default credentials. User: pi - PW: raspberry
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# Disabling the OTG mode to use a keyboard and mouse again
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**WARNING: Untested**
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1. Comment out the dwg2 line in `/boot/firmware/config.txt` using a `#` in front of the line
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```
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[all]
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#dtoverlay=dwg2
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```
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1. Comment out the dwg2 line in `/etc/modules` using a `#` in front of the line
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```
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#dwg2
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```
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1. Disable the gadget service
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```
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systemctl disable serial-ether-gadget.service
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```
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1. Disable the getty
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```
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systemctl disable serial-getty@ttyGS0.service
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```
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# Connecting over the USB ethernet to ssh into your Pi
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I have not tested this procedure because the serial console and normal network connection is sufficient for me --foley
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https://www.raspberrypi.com/news/usb-gadget-mode-in-raspberry-pi-os-ssh-over-usb/
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# Untested
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Here are items that bear investigating but haven't been tested yet
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- [Modify Imager manifest to install otg](https://github.com/raspberrypi/rpi-imager/tree/main/doc/local_json)
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