Check for GADGET_MODE in boot/firmware to enable

Scripts/gadget.sh

@@ -9,6 +9,13 @@ if [ $(id -u) -ne 0 ]; then
     exit 1
 fi
 
+if [ -f /boot/firmware/GADGET_MODE ]; then
+    systemd-cat -t gadget.sh -p info echo "/boot/firmware/GADGET_MODE exists:  GADGET mode enabled"
+else
+    systemd-cat -t gadget.sh -p warning echo "/boot/firmware/GADGET_MODE missing:  GADGET mode disabled"
+    systemctl disable serial-getty@ttyGS0.service
+    exit 1
+fi
 
 # Is the dwc2 overlay installed?  Nothing will work if it isn't.
 if [ -d /sys/class/udc ] && [ -n "$(ls -A /sys/class/udc)" ]; then

gadget.md

@@ -18,14 +18,6 @@ Make sure you have your USB cable plugged into the left port **USB** and not the
 ```
 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
@@ -94,7 +86,38 @@ This is similar to the procedure for accessing an Arduino.
     ```
 1. Press enter and you will be prompted to log in to the Pi with default credentials. User: pi - PW: raspberry
 
-# Disabling the OTG mode to use a keyboard and mouse again
+# Enabling/Disabling the OTG mode to use a keyboard and mouse again
+
+**WARNING: Untested**
+1. Disable:  Delete a file called `GADGET_MODE` in the boot partition/drive when not on a pi.  If the Pi is booted, you can delete `sudo rm /boot/firmware/GADGET_MODE` and reboot
+1. Enable:  create a file called `GADGET_MODE` in the boot partition/drive when not on a pi.  If the Pi is booted, you can create `sudo touch /boot/firmware/GADGET_MODE` and reboot
+
+# Connecting over the USB ethernet to ssh into your Pi
+
+I have not tested this procedure because the serial console and normal network connection is sufficient for me --foley
+
+https://www.raspberrypi.com/news/usb-gadget-mode-in-raspberry-pi-os-ssh-over-usb/
+
+
+# Untested
+ Here are items that bear investigating but haven't been tested yet
+ 
+ - [Modify Imager manifest to install otg](https://github.com/raspberrypi/rpi-imager/tree/main/doc/local_json)
+ 
+# Old DWC Instructions (for older versions)
+
+## Setting up
+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
+```
+
+
+## Disabling the OTG mode to use a keyboard and mouse again
 
 **WARNING: Untested**
 1. Comment out the dwg2 line in `/boot/firmware/config.txt` using a `#` in front of the line
@@ -114,16 +137,3 @@ This is similar to the procedure for accessing an Arduino.
     ```
 	systemctl disable serial-getty@ttyGS0.service
 	```
-
-# Connecting over the USB ethernet to ssh into your Pi
-
-I have not tested this procedure because the serial console and normal network connection is sufficient for me --foley
-
-https://www.raspberrypi.com/news/usb-gadget-mode-in-raspberry-pi-os-ssh-over-usb/
-
-
-# Untested
- Here are items that bear investigating but haven't been tested yet
- 
- - [Modify Imager manifest to install otg](https://github.com/raspberrypi/rpi-imager/tree/main/doc/local_json)
-