what is the best way to start learning about RTOS??

Here's a brief overview on RTOS for those that aren't looking to commit to a book or code just yet. [Credit to Professor Jim Peckol at UW]

An operating system has to provide 3 essential things:

1. Task Scheduling - The scheduler determines which task to run and when a task will run
2. Task Dispatching - The dispatcher handles the necessary operations to get a task ready to go
3. Intertask Communication - This is the mechanism that handles how you exchange data and information between tasks and processes on the same machine or from other machines

These 3 essential things are what makes up the smallest portion of an OS called the Kernel.

A real time operating system is just a special purpose operating system. The 'real time' part of the name does not mean that the system responds quickly, it just means that there are rigid time requirements that must be met. If these time requirements are not met, your results can become inaccurate or unreliable.

So you want to use a RTOS when you need to monitor and control physical  processes in a timely manner. The constraints you have deal with when using RTOS are tight scheduling, predictability, and robustness.

There are two kinds of RTOS:

1. Hard Real Time - System delays are known or at least bounded. Said to be operating correctly if the system can return results within any time constraints.
2. Soft Real Time - Critical tasks get priority over other tasks and will retain priority until the task is completed. This is another way of saying that real time tasks cannot be kept waiting indefinitely. Soft real time makes it easier  to mix the system with other systems.

Check out freertos.org for more!

Clem

The argument is very vast!

I think the better approach is to start to understand basics using a very simple RTOS like freeRTOS

On freeRTOS site there is a good tutorial

RTOS Tutorial - Using an RTOS on small embedded computers

This is a set of videos that will help you get started with freeRTOS. More videos shall be uploaded in the series soon. Below is the link:

https://www.youtube.com/playlist?list=PLEfMFrwVdbPYzMgeaLiFRb4ogjV8m3lt6

Miro Samek, Quantum Leaps,  has a series of Embedded Tutorials on YouTube which includes a newer RTOS series.   For the most part, he uses the low cost TM4C123GXL Launchpad from TI but the concepts can be used with other boards as well.

https://www.state-machine.com/

https://www.youtube.com/channel/UCMGXFEew8I6gzjg3tWen4Gw

TI has a series that is based on Their TI-RTOS:

https://training.ti.com/ti-rtos-workshop-series-1-10-welcome

The Mastering RTOS course from FastBit on Udemy is a good course for getting started with RTOS using a STM board.   There has been some changes to the course where he has eliminated the use of Eclipse, but otherwise it is a good course.  Also, it is currently only $9.99US.

https://www.udemy.com/mastering-rtos-hands-on-with-freertos-arduino-and-stm32fx/

Old post, but for anyone interested, these books were useful when I was learning about it..

Real Time Systems and Programming Languages - Burns, Wellings

Software Design for Real-Time Systems - Cooling

It's also fun to try to attempt to create your own experimental RTOS just as a learning thing.. this book is a bit basic, but shows you how to do that..:

uC/OS The Real Time Kernel - Labrosse

I second the Labrosse books for RTOS learning.  This was used in a Uni class on RTOS using a Renesas RX62N but there are other versions of the book for other dev boards as well.

https://www.micrium.com/books/ucosiii/

An Embedded Software Primer by David E. Simon is an easy intro to Embedded Systems as well as RTOS.