Had problems with communication between the RPi 4 and CS-108G+ radio. Radio connected as device: /dev/ttyACM0.
Found that changing permissions of the device to 777 improved making the connection with all my ham radio apps such as flrig, fldigi, CQRLOG, etc. Had been entering the command,"sudo chmod 777 /dev/ttyACM0" after turning on the radio. Wanted a way to make this happen automatically.
Used nano to create a udev to trigger this when the RPi detects the radio is connected. File name is "etc/udev/rules.d/11-my.rules". Contains this line to trigger the action: KERNEL=="ttyACM0", MODE="0777" Added bold and underline for emphasis, not needed in file.
Works well and no more issues with this. Another item I had was the micro USB port on the radio was a little loose. So wrapped a couple of rubber bands around the cable, then stretched them over the front of the radio. Keeps the plug nice and tight.
Hope this useful for a few hams out there.