The preceding chapters covered the four elements of embedded Linux and showed you, step-by-step, how to build a toolchain, a bootloader, a kernel, and a root filesystem, and then combine them into a basic embedded Linux system. And there are a lot of steps! Now it is time to look at ways to simplify the process by automating it as much as possible. I will look at how embedded build systems can help, and look at two in particular: Buildroot and the Yocto Project. Both are complex and flexible tools which would require an entire book to adequately describe how they work. In this chapter, I only want to show you the general ideas behind build systems. I will show you how to build a simple device image to get an overall feel of the system and then how to make some useful changes, using the Nova board example from the previous chapters.
The process of creating a system manually, as described in Chapter 5, Building a Root Filesystem, is called the roll your own (RYO) process. It has the advantage that you are in complete control of the software and you can tailor it to do anything you like. If you want it to do something truly odd but innovative, or if you want to reduce the memory footprint to the smallest possible, RYO is the way to go. But, in the vast majority of situations, building manually is a waste of time and produces inferior, unmaintainable systems.
They are usually built incrementally over a period of months, often undocumented and seldom recreated from scratch because nobody had a clue where each part came from.