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

Moving from bootloader to kernel

When the bootloader passes control to the kernel it has to pass some basic information to the kernel, which may include some of the following:

  • On PowerPC and ARM architectures: a number unique to the type of the SoC
  • Basic details of the hardware detected so far, including at least the size and location of the physical RAM, and the CPU clock speed
  • The kernel command line
  • Optionally, the location and size of a device tree binary
  • Optionally, the location and size of an initial RAM disk

The kernel command line is a plain ASCII string which controls the behavior of Linux, setting, for example, the device that contains the root filesystem. I will look at the details of this in the next chapter. It is common to provide the root filesystem as a RAM disk, in which case it is the responsibility of the bootloader to load the RAM disk image into memory. I will cover the way you create initial RAM disks in Chapter 5, Building a Root Filesystem.

The way this information is passed...