Chapter 3. All About Bootloaders

The bootloader is the second element of embedded Linux. It is the part that starts the system up and loads the operating system kernel. In this chapter, I will look at the role of the bootloader and, in particular, how it passes control from itself to the kernel using a data structure called a device tree, also known as a flattened device tree or FDT. I will cover the basics of device trees so that you will be able to follow the connections described in a device tree and relate it to real hardware.

I will look at the popular open source bootloader U-Boot and see how to use it to boot a target device and also how to customize it to a new device. Finally, I will take a quick look at Barebox, a bootloader that shares its past with U-Boot but which has, arguably, a cleaner design.