Book Image

Hands-On RTOS with Microcontrollers

By : Brian Amos
Book Image

Hands-On RTOS with Microcontrollers

By: Brian Amos

Overview of this book

A real-time operating system (RTOS) is used to develop systems that respond to events within strict timelines. Real-time embedded systems have applications in various industries, from automotive and aerospace through to laboratory test equipment and consumer electronics. These systems provide consistent and reliable timing and are designed to run without intervention for years. This microcontrollers book starts by introducing you to the concept of RTOS and compares some other alternative methods for achieving real-time performance. Once you've understood the fundamentals, such as tasks, queues, mutexes, and semaphores, you'll learn what to look for when selecting a microcontroller and development environment. By working through examples that use an STM32F7 Nucleo board, the STM32CubeIDE, and SEGGER debug tools, including SEGGER J-Link, Ozone, and SystemView, you'll gain an understanding of preemptive scheduling policies and task communication. The book will then help you develop highly efficient low-level drivers and analyze their real-time performance and CPU utilization. Finally, you'll cover tips for troubleshooting and be able to take your new-found skills to the next level. By the end of this book, you'll have built on your embedded system skills and will be able to create real-time systems using microcontrollers and FreeRTOS.
Table of Contents (24 chapters)
Section 1: Introduction and RTOS Concepts
Section 2: Toolchain Setup
Section 3: RTOS Application Examples
Section 4: Advanced RTOS Techniques

Using mutexes

Mutex stands for mutual exclusion – they are explicitly designed to be used in situations where access to a shared resource should be mutually exclusive – meaning the shared resource can only be used by one piece of code at a time. At their heart, mutexes are simply binary semaphores with one (very important) difference: priority inheritance. In the previous example, we saw the highest-priority task waiting on two lower-priority tasks to complete, which caused a priority inversion. Mutexes address this issue with something called priority inheritance.

When a higher-priority task attempts to take a mutex and is blocked, the scheduler will elevate the priority of the task that holds the mutex to the same level as the blocked task. This guarantees that the high-priority task will acquire the mutex and run as soon as possible.