Interesting read. I'm surprised Amazon haven't blocked UART access in bootrom mode, considering there's an efuse they can blow, from the bootloader (LK) environ

Interesting read. I'm surprised Amazon haven't blocked UART access in bootrom mode, considering there's an efuse they can blow, from the bootloader (LK) environment, that will permanently disable it. As an example, Motorola did this on their Mediatek-based phones as part of a firmware update.