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 (22 chapters)
Mastering Embedded Linux Programming
About the Author
About the Reviewers

Understanding scheduling latency

Real-time threads need to be scheduled as soon as they have something to do. However, even if there are no other threads of the same or higher priority, there is always a delay from the point at which the wake up event occurs – an interrupt or system timer – to the time that the thread starts to run. This is called scheduling latency. It can be broken down into several components, as shown in the following diagram:

Firstly, there is the hardware interrupt latency from the point at which an interrupt is asserted until the ISR (interrupt service routine) begins to run. A small part of this is the delay in the interrupt hardware itself but the biggest problem is interrupts disabled in the software. Minimizing this IRQ off time is important.

The next is interrupt latency, which is the length of time until the ISR has serviced the interrupt and woken up any threads waiting on this event. It is mostly dependent on the way the ISR was written. Normally it should take...