Access to a console can be mandatory when you SBC doesn't work as expected (e.g Network or HDMI output doesn't work). When SSH/Display access isn't possible access to console via UART is the best way to get a clue where your SBC hangs. This short tutorial should give you an introduction how this works. For some boards, armbian implements an USB gadget mode (a 'fake' serial console over microUSB) describen below. As a reminder an USB-UART bridge is always prefered over USB gadget mode whenever po