= Startup sequence =

U-Boot implements a text console on the serial port. This console can be used to stop the startup sequence to allow an interactive session with the human operator. This is very useful during debug operations, but by default any character the bootloader receives during the startup sequence stops this process. As a side effect, any spurious character received from the serial port devoted to the console is able to prevent the bootloader to complete the automatic boot process (and typically to start the operating system).

For this reason before moving to the field it is highly recommended to configure the bootloader to halt the sequence when receiving a specific string. Fortunately, Autoboot process is deeply configurable: parameters defining the retry behaviour and the strings used to stop booting can be specified. Please read the README.autoboot file, provided inside the documentation directory of the U-Boot sources, for more details.