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Real-Time Operating Systems – So That's How They Work! PDF Print E-mail
Clive 'Max' Maxfield
Clive 'Max' Maxfield
I've long wanted to know more about how a Real-Time Operating System (RTOS) performs its magic and how to use one of these little rascals, but there's surprisingly little written about this subject. Fortunately things are changing. First of all our own Mike Hibbett has just written a really interesting four-part series of Pic n’ Mix articles on this very topic (Part 1 appeared in the October 2009 issue of EPE). Futhermore, I was just introduced to a book called "µC/OS-III – The Real-Time Kernel" l Click Here to see a full review, including a video, by yours truly.) Just to make sure we're all tap-dancing to the same drum beat, let's take a step back and set the scene. It's possible to create a simple computer program that can be executed directly on a microprocessor or microcontroller. More usually, we run a special piece of software called an Operating System (OS), which is responsible for coordinating resources and managing any application-level programs running on the machine.

In the case of a general-purpose operating system, there is no guarantee that anything will happen at a particular time. If you launch your web browser, for example, it may appear on your screen almost immediately or (depending on what other tasks the operating system is currently juggling) it may take a few seconds. Although this is often somewhat frustrating, we learn to live with it.

But now consider something like an industrial controller in charge of a production line. When a sensor detects something happening in the real world, it may be required for the operating system to do something NOW! In order to address this, we have the concept of a Real-Time Operating System (RTOS) – such a beast guarantees to respond to external stimuli in a certain amount of time.

Of course the above is a gross simplification. We might have large numbers of different tasks, each with their own priority level (some tasks may share the same priority), so the OS has to manage these tasks, scheduling, synchronization, message passing, switching, interrupts, resources, memory... and all sorts of "stuff".

And so we come to µC/OS-III (pronounced "Micro-C, O-S Three"), which is a state-of-the-art, scalable, ROMable, pre-emptive real-time kernel that manages an unlimited number of tasks. (Don’t worry if you don’t understand what any of these terms mean – you will if you read the book.)

Actually, I should point out that this book is not targeted at absolute beginners – readers need to have a good understanding of microprocessors and microcontrollers and C programming.

Unfortunately this book is not cheap ($199.95 from Amazon), but it's actually a rather good deal when you understand that it comes with an evaluation board that plugs into your PC via a USB cable. In conjunction with the free development environment that you can download over the Internet, you can really sink your teeth into learning all about RTOSes (I'm not sure what the plural should be here).

If you haven’t already done so, Click Here to see a full review, including a video, by yours truly.
 
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