Summary

Every system needs a bootloader to bring the hardware to life and to load a kernel. U-Boot has found favor with many developers because it supports a useful range of hardware and it is fairly easy to port to a new device. Over the last few years, the complexity and ever increasing variety of embedded hardware has led to the introduction of the device tree as a way of describing hardware. The device tree is simply a textual representation of a system that is compiled into a devicetree binary (dtb) and which is passed to the kernel when it loads. It is up to the kernel to interpret the device tree and to load and initialize drivers for the devices it finds there.

In use, U-Boot is very flexible, allowing images to be loaded from mass storage, flash memory, or a network, and booted. Likewise, Barebox can achieve the same but with a smaller base of hardware support. Despite its cleaner design and POSIX-inspired internal APIs, at the time of writing it does not seem to have been accepted beyond its own small but dedicated community.

Having covered some of the intricacies of booting Linux, in the next chapter you will see the next stage of the process as the third element of your embedded project, the kernel, comes into play.