Book Image

Mastering Embedded Linux Programming

By : Chris Simmonds
Book Image

Mastering Embedded Linux Programming

By: Chris Simmonds

Overview of this book

Mastering Embedded Linux Programming takes you through the product cycle and gives you an in-depth description of the components and options that are available at each stage. You will begin by learning about toolchains, bootloaders, the Linux kernel, and how to configure a root filesystem to create a basic working device. You will then learn how to use the two most commonly used build systems, Buildroot and Yocto, to speed up and simplify the development process. Building on this solid base, the next section considers how to make best use of raw NAND/NOR flash memory and managed flash eMMC chips, including mechanisms for increasing the lifetime of the devices and to perform reliable in-field updates. Next, you need to consider what techniques are best suited to writing applications for your device. We will then see how functions are split between processes and the usage of POSIX threads, which have a big impact on the responsiveness and performance of the final device The closing sections look at the techniques available to developers for profiling and tracing applications and kernel code using perf and ftrace.
Table of Contents (16 chapters)
15
Index

What does a bootloader do?


In an embedded Linux system, the bootloader has two main jobs: basic system initialization and the loading of the kernel. In fact, the first job is somewhat subsidiary to the second in that it is only necessary to get as much of the system working as is needed to load the kernel.

When the first lines of bootloader code are executed, following power-on or a reset, the system is in a very minimal state. The DRAM controller will not have been set up so main memory is not accessible, likewise other interfaces will not have been configured so storage accessed via NAND flash controllers, MMC controllers, and so on, are also not usable. Typically, the only resources operational at the beginning are a single CPU core and some on-chip static memory. As a result, system bootstrap consists of several phases of code, each bringing more of the system into operation.

The early boot phase stops once the interfaces required to load a kernel are working. That includes main memory...