Mastering the FreeRTOS™ Real Time Kernel, A Hands-On Tutorial Guide

About FreeRTOS

FreeRTOS is solely owned, developed, and maintained by Real Time Engineers Ltd. Real Time Engineers Ltd. have been working in close partnership with the world’s leading chip companies for well over a decade to provide you award winning, commercial grade, and completely free high quality software.

FreeRTOS is ideally suited to deeply embedded real-time applications that use microcontrollers or small microprocessors. This type of application normally includes a mix of both hard and soft real-time requirements.

Soft real-time requirements are those that state a time deadline—but breaching the deadline would not render the system useless. For example, responding to keystrokes too slowly might make a system seem annoyingly unresponsive without actually making it unusable.

Hard real-time requirements are those that state a time deadline—and breaching the deadline would result in absolute failure of the system. For example, a driver’s airbag has the potential to do more harm than good if it responded to crash sensor inputs too slowly.

FreeRTOS is a real-time kernel (or real-time scheduler) on top of which embedded applications can be built to meet their hard real-time requirements. It allows applications to be organized as a collection of independent threads of execution. On a processor that has only one core, only a single thread can be executed at any one time. The kernel decides which thread should be executed by examining the priority assigned to each thread by the application designer. In the simplest case, the application designer could assign higher priorities to threads that implement hard real-time requirements, and lower priorities to threads that implement soft real-time requirements. This would ensure that hard real-time threads are always executed ahead of soft real-time threads, but priority assignment decisions are not always that simplistic.

Do not be concerned if you do not fully understand the concepts in the previous paragraph yet. The following chapters provide a detailed explanation, with many examples, to help you understand how to use a real-time kernel, and how to use FreeRTOS, in particular.