The four elements of embedded Linux

Every project begins by obtaining, customizing, and deploying these four elements: the toolchain, the bootloader, the kernel, and the root filesystem. This is the topic of the first section of this book.

• Toolchain: This is the cross compiler and other tools needed to create code for your target device. A cross compiler generates machine code for a target CPU architecture while running on a different host CPU architecture.
• Bootloader: This is a bare metal program that initializes the board and the Linux kernel. The term “bare metal” means the program runs directly on the CPU, not on top of an OS.
• Kernel: This is the heart of the system, managing system resources and interfacing with the hardware.
• Root filesystem: This contains the libraries and programs that are run once the kernel has completed its initialization.

There is also a fifth element not mentioned here. That is the collection of programs specific to your embedded application that make the device do whatever it is supposed to do, be it weighing groceries, displaying movies, controlling a robot, or flying a drone.

Typically, you will be offered some or all of these elements as a package when you buy your SoC or board. But for the reasons mentioned earlier, they may not be the best choices for you. In the first eight chapters, I will give you the background to make the right selection and introduce two tools that automate the whole process for you: Buildroot and The Yocto Project.