# 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
Make sure you have your USB cable plugged into the left port **USB** and not the right port marked **PWR**.
1. Open a connection to the device
1. Become root (the superuser)
    ```
	sudo su
	```
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)
   ```
    echo "dtoverlay=dwc2" >> /boot/firmware/config.txt
	```
1. We add the required module `dwc2` for loading at startup
    ```
	echo "dwc2" >> /etc/modules
	```
1. Check that we can load the libcomposite module
    ```
    modprobe libcomposite
	```
1. 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		
	  ```
1. 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
	  ```
1. Install the systemd script
      `cp serial-ether-gadget.service /lib/systemd/system/.`
1. Enable the getty (which connects a login terminal to the serial port)
      ```
	  systemctl enable serial-getty@ttyGS0.service
	  ```
1. 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

## Windows
- Putty:  https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
- MobaXterm: https://mobaxterm.mobatek.net/

## Linux
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.
1.  Start the Linux VM if you haven't already
1. Menu: Devices > USB
1. Look for "Silicon Labs CP210x USB to UART Bridge" and click on it.
1. check if port /dev/ttyUSB0 is found. The Pi will most often be accessible over this port.
    ```
    ls -l /dev/ttyU*
    ```
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:
    ```
    sudo usermod -a -G dialout <username>
	```
1. You will use the GNU `screen` application in Linux to access the Pi.  You can install it with:
    ```
    sudo apt install screen
	```
1. You should now gain access to the Pi with:
	```
  ` sudo screen /dev/ttyUSB0 115200
    ```
1. Press enter and you will be prompted to log in to the Pi with default credentials. User: pi - PW: raspberry