What this book covers
Chapter 1, Starting Out, sets the scene by describing the embedded Linux ecosystem and the choices available to you as you start your project.
Chapter 2, Learning about Toolchains, describes the components of a toolchain and shows you how to create a toolchain for cross-compiling code for the target board. It describes where to get a toolchain and provides details on how to build one from the source code.
Chapter 3, All about Bootloaders, explains the role of the bootloader in loading the Linux kernel into memory, and uses U-Boot as an example. It also introduces device trees as the mechanism used to encode the details of the hardware in almost all embedded Linux systems.
Chapter 4, Configuring and Building the Kernel, provides information on how to select a Linux kernel for an embedded system and configure it for the hardware within the device. It also covers how to port Linux to the new hardware.
Chapter 5, Building a Root Filesystem, introduces the ideas behind the user space part of an embedded Linux implementation by means of a step-by-step guide on how to configure a root filesystem.
Chapter 6, Selecting a Build System, covers two commonly used embedded Linux build systems, Buildroot and the Yocto Project, which automate the steps described in the previous four chapters.
Chapter 7, Developing with Yocto, demonstrates how to build system images on top of an existing BSP layer, develop onboard software packages with Yocto's extensible SDK, and roll your own embedded Linux distribution complete with runtime package management.
Chapter 8, Yocto under the Hood, is a tour of Yocto's build workflow and architecture including an explanation of Yocto's unique multi-layer approach. It also breaks down the basics of BitBake syntax and semantics with examples from actual recipe files.
Chapter 9, Creating a Storage Strategy, discusses the challenges created by managing flash memory, including raw flash chips and embedded MMC (eMMC) packages. It describes the filesystems that are applicable to each type of technology.
Chapter 10, Updating Software in the Field, examines various ways of updating the software after the device has been deployed, and includes fully managed Over-the-Air (OTA) updates. The key topics under discussion are reliability and security.
Chapter 11, Interfacing with Device Drivers, describes how kernel device drivers interact with the hardware by implementing a simple driver. It also describes the various ways of calling device drivers from user space.
Chapter 12, Prototyping with Breakout Boards, demonstrates how to prototype hardware and software quickly using a pre-built Debian image for the BeagleBone Black together with a peripheral breakout board. You will learn how to read datasheets, wire up boards, mux device tree bindings, and analyze SPI signals.
Chapter 13, Starting Up – The init Program, explains how the first user space
program–init–starts the rest of the system. It describes three versions of the init program, each suitable for a different group of embedded systems, ranging from the simplicity of the BusyBox init, through System V init, to the current state-of-the-art approach, systemd.
Chapter 14, Starting with BusyBox runit, shows you how to use Buildroot to divide your system up into separate BusyBox runit services each with its own dedicated process supervision and logging like that provided by systemd.
Chapter 15, Managing Power, considers the various ways that Linux can be tuned to reduce power consumption, including dynamic frequency and voltage scaling, selecting deeper idle states, and system suspend. The aim is to make devices that run for longer on a battery charge and also run cooler.
Chapter 16, Packaging Python, explains what choices are available for bundling Python modules together for deployment and when to use one method over another. It covers pip, virtual environments, conda, and Docker.
Chapter 17, Learning about Processes and Threads, describes embedded systems from the point of view of the application programmer. This chapter looks at processes and threads, inter-process communications, and scheduling policies.
Chapter 18, Managing Memory, introduces the ideas behind virtual memory and how the address space is divided into memory mappings. It also describes how to measure memory usage accurately and how to detect memory leaks.
Chapter 19, Debugging with GDB, shows you how to use the GNU debugger, GDB, together with the debug agent, gdbserver, to debug applications running remotely on the target device. It goes on to show how you can extend this model to debug kernel code, making use of the kernel debug stubs with KGDB.
Chapter 20, Profiling and Tracing, covers the techniques available to measure the system performance, starting from whole system profiles and then zeroing in on particular
areas where bottlenecks are causing poor performance. It also describes how to use Valgrind to check the correctness of an application's use of thread synchronization and memory allocation.
Chapter 21, Real-Time Programming, provides a detailed guide to real-time programming on Linux, including the configuration of the kernel and the PREEMPT_RT real-time kernel patch. The kernel trace tool, Ftrace, is used to measure kernel latencies and show the effect of the various kernel configurations.