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µC/OS-III (pronounced “Micro C O S Three) is a scalable, ROMable, preemptive real-time kernel that manages an unlimited number of tasks. µC/OS-III is a third-generation kernel and offers all of the services expected from a modern real-time kernel, such as resource management, synchronization, inter-task communications, and more. However, µC/OS-III offers many unique features not found in other real-time kernels, such as the ability to complete performance measurements at run-time, to directly signal or send messages to tasks, achieve pending on multiple kernel objects, and more.
Why a new µC/OS version?
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µC/OS-III also provides additional features that better exploit the capabilities of today’s newer processors. Specifically, µC/OS-III was designed with 32-bit processors in mind, although it certainly works well with 16- and even several 8-bit processors.
What’s New About This Book?
The MicroC/OS-II book focused primarily on documenting the μC/OS-II product with a great, yet brief, RTOS introduction. This book changes that focus. This time, the spotlight is on real-time kernels and Real-Time Operating Systems (RTOS), with μC/OS-III used as a reference. In-depth product documentation is now provided in the appendices.
By taking this approach, the intent is to reach a larger target audience, especially those from industry and academia alike that are completely new to the topic of RTOS, This book is also suitable for use as the foundation of a generic RTOS class.
From a didactic perspective, every person has four different learning styles:
- Activist (A)
- Observational (O)
- Theoretical (T)
- Pragmatic (P)
The style that is more dominant differs from person to person. Based on these learning styles, there are strong improvements over the previous book, MicroC/OS-II, The Real-Time Kernel, which primarily focused on theoretical and, thanks to the good illustrations, also the observational learning styles. However, activist and pragmatic styles were somewhat missing. This book answers more questions for the pragmatist concerning: Why would I be interested in this? What could I use this for? What does this mean for my project? How does this help me get the job done?
Typically, books completely lack an activist learning style. This is a tricky one for a book because the question then becomes, how do you get readers to become active and do something with the material? That’s where the companion evaluation board and tools come in. This two-part text, combined with tools and evaluation board, enable readers to receive the material, and begin to have a hands-on experience right away.
This book is split into two parts. The first part describes real-time kernels in generic terms, using μC/OS-III as a real-life example. The second part, which actually looks like a completely different book, provides examples using a popular microprocessor or microcontroller. As mentioned, the book is accompanied by a matching evaluation board and such tools as a compiler, assembler, linker, and debugger, which enable the reader to experiment with μC/OS-III and become proficient with its use.
In summary, the general topic of RTOS is now the prevailing topic of this book. Explaining the concept of RTOS in combination with μC/OS-III, an evaluation board and tools simply makes sense.
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µC/OS-III was designed with 32-bit processors in mind, although it certainly works well with 16- and even several 8-bit processors.
µC/OS-III Goals
The main goal of μCµC/OS-III is to provide a best-in-class real-time kernel that literally shaves months of development time from an embedded-product schedule. Using a commercial real-time kernel such as μCµC/OS-III provides a solid foundation and framework to the design engineer dealing with the growing complexity of embedded designs.
Another goal for μCµC/OS-III, and therefore this bookdocumentation, is to explain inner workings of a commercial-grade kernel. This understanding will assist the reader in making logical design decisions and informed tradeoffs trade-offs between hardware and software that make sense.
Intended Audience
This book documentation is written for embedded systems programmers, consultants, hobbyists and students interested in understanding the inner workings of a real-time kernel. μCµC/OS-III is not just a great learning platform, but also a commercial-grade software package ready to be part of a range of products.
To get the most from this bookdocumentation, it is assumed that the reader has a good working knowledge of microprocessors, microcontrollers, and/or Digital Signal Processors (DSPs). That knowledge should extend to CPU instructions, interrupts, I/O devices, RAM and ROM or Flash, memory addresses, and stack pointers.
It is also expected that the reader will have a good working knowledge of the C programming language and assembly language.
The
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µC/OS Story
The μCµC/OS story started when, in 1989, I joined Dynalco Controls in Fort Lauderdale, Florida, and began working on the design of a new microprocessor-based ignition control system for a large industrial reciprocating engine.
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With a new kernel in hand, there was finally a handy means of developing multitasking applications. The operating system, consisted of little more than a single C file and allowed up to 64 tasks to be created in a single application. Each task was required to be have a unique priority. The highest priority task that was ready to run when the operating system’s scheduler was invoked was given control of the CPU. μCµC/OS was preemptive, so scheduling could occur at practically any time.
Efficient task scheduling was actually one of many services offered by μCµC/OS. The operating system also facilitated inter-task communication (via message queues and mailboxes) and task synchronization (through semaphores). All elements of μCµC/OS were designed to be both highly dependable and easy to use.
Presumably, most kernel developers have similar goals in mind when they write new software. I was especially well equipped to meet these goals, in part because of my punctilious coding style. Throughout my career, I focused on consistency and documentation. I began using formal coding standards in 1984, and the consistency of the μCµC/OS code is a testimony to this process.
μCµC/OS was designed according to the stringent standards that I created and promulgated at Dynalco. The operating system’s source code featured liberal spacing, carefully worded comments, and consistent naming. Offering further evidence of the prudent coding techniques, the kernel was also highly portable. Although μCµC/OS, like its kernel peers, featured a small number of processor-specific functions, these routines were clearly separated from other portions of the operating system. Engineers could easily adapt μCµC/OS to new CPU architectures.
Unfortunately, I was the only one to know about the virtues of μCµC/OS. Eager to describe my new software to others, I wrote an in-depth paper explaining the inner workings of μCµC/OS. There was plenty to say, and my final paper was approximately 70 pages in length.
I offered my paper to C User’s Journal, and they rejected it on the grounds that it was too long and that its subject matter wasn’t fresh. The magazine had already published several kernel articles, and this was just one more. Convinced that my article was unique, I offered it to Embedded Systems Programming. The editor of this periodical likewise expressed misgivings, but I convinced him that μCµC/OS was attention-worthy. I explained that the operating system was comparable in quality to products that major embedded software companies offered (and better than at least two). I also explained that the source code for μCµC/OS could actually be placed on the publication’s bulletin board service (BBS).
Embedded Systems Programming published a trimmed-down version of the paper as a two-part series. Both issues generated strong responses. Engineers were grateful that the inner workings of a high-quality kernel were revealed, and they downloaded the μCµC/OS source code in droves. kernel vendors, on the other hand, were less than thrilled with the article. In fact, the vendor of the low cost kernel was especially upset claiming that I had copied his work. Imagine that I would base μCµC/OS on software that didn’t work!
There would soon be even more reason for the kernel vendors to be upset. Shortly after my article appeared in Embedded Systems Programming, R & D Publications, publisher of C User’s Journal contacted me, and they were interested in printing an entire μCµC/OS book.
Originally, the plan for the book simply involved printing all of the material that I had originally submitted to C User’s Journal. Had I taken that route, the resulting book would have been approximately 80 pages or so in length. To make the most of this opportunity, I prepared a comprehensive text. With the consent of R & D, I spent the next several months writing. In late 1992, my first book, aptly titled μCµC/OS, The Real-Time Kernel, was released. The book had 250 pages, and was available in paperback form.
Although initial sales of the book were somewhat disappointing, R & D advertised μCµC/OS, The Real-Time Kernel each month in C User’s Journal. At the same time, I was beginning to gain attention as a kernel expert. In the spring of 1993, I was invited to speak at the Embedded Systems Conference (ESC) in Atlanta, Georgia, where I described operating system fundamentals to a highly receptive audience of more than 70 embedded enthusiasts. Within a few years, I was an ESC fixture, delivering my kernel lectures to hundreds of engineers at each conference.
While my popularity as a speaker rose, interest in my book also picked up steam. After its slow start, μCµC/OS, The Real-Time Kernel, went on to sell more than 15,000 copies.
Thanks to the success of my book, the number of engineers using μCµC/OS increased substantially throughout the 1990s. Developers easily adapted the operating system to new hardware platforms, and were designing a myriad of μCµC/OS-based applications. Although several μCµC/OS users simply tinkered with the operating system in their spare time, many engineers used the software commercially in complex and demanding projects. Comments and suggestions from μCµC/OS users helped me to continue to refine and evolve the operating system.
For several years, only minor changes were made to μCµC/OS. However, when R & D asked me to write a second edition, I decided that a substantial update of both the operating system and the book was warranted. The updated operating system became μCµC/OS-II.
A quick glance at the μCµC/OS-II files revealed that this operating system was different from μCµC/OS. Whereas all of the processor-independent code incorporated by μCµC/OS was contained in a single C file, μCµC/OS-II spanned multiple files, each corresponding to one of the operating system’s services. μCµC/OS-II also offered many features that its predecessor lacked, including stack-checking capabilities, hook functions, and a safe means to dynamically allocate memory.
To fully describe all of the new operating system’s features, I nearly doubled the size of the book. Just as the latest version of the software received a new name, the new edition became MicroC/OS-II, The Real-Time Kernel. (“Micro” was used in place of “μ” “µ” because titles incorporating Greek letters posed problems for many book retailers.) Unlike my first text, the new book would be a hardcover.
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Among the thousands of readers of my books using the software, there were many kernel rookies. For them, the book provided thorough and accessible coverage of operating system fundamentals. Many university professors recognized the book’s appeal to new kernel users and started designing entire courses around μCµC/OS-II. Soon college graduates whose kernel training focused on the operating system made their way into the workforce, where they continued to use μCµC/OS-II.
While students gravitated to μCµC/OS-II because of my book and readily available source code, a substantial number of engineers using μCµC/OS-II commercially selected the software for its reliability. Definitive proof of the operating system’s reliability was provided in July 2000, when DO-178B Level A certification was conferred on an avionics product incorporating μCµC/OS-II. This certification, recognized by the Federal Avionics Administration (FAA), is awarded to software deemed safe enough to be used in aircraft. To this day, there are few operating systems that have successfully completed the rigorous testing that certified software must undergo.
DO-178B certification is only one of μCµC/OS-II’s credentials. Additional certifications include Food and Drug Administration (FDA) pre-market notification (510(k)), pre-market approval (PMA) for medical devices, and IEC-61508 for industrial controls. Compliance with such standards is critical within industry segments; however, the certifications also have value for engineers in other industries as they evidence reliability, documentation, and time-to-market advantages beneficial to any design.
As the decade came to a close, I still worked full time at Dynalco, and experienced difficulty keeping up with the demand for the operating system. I felt obligated to respond to each μCµC/OS-II user that contacted me, and the flow of messages into my inbox was unrelenting. Since I could no longer treat the operating system as a side project, I made the decision to found my own software company. In September 1999, MicriμmMicriµm, officially came into being. Micriμm Micriµm comes from the word ‘Micro’ (for microprocessors or microcontrollers) and ‘ium’ (which means the Universe of) and thus, Micriμm Micriµm means the Universe of Microprocessors (as seen through the eyes of software).
In the months before incorporating MicriμmMicriµm, I began working on a second edition of the μCµC/OS-II book, which made its debut in November 1999 and was accompanied by a new version of the kernel. Two major features to the operating system were added: event flags and mutual exclusion semaphores. These new features, fully described in the book, were heartily welcomed by μCµC/OS-II users. The book itself was similarly embraced; the second edition of MicroC/OS-II, The Real-Time Kernel quickly became common sight on the bookshelves of embedded software developers. In fact, the MicroC/OS-II book is the most popular embedded systems book ever sold.
Micriμm Micriµm expanded. Engineers were hired to adapt μCµC/OS-II to new hardware platforms and develop a bevy of example projects and application notes. A long-time friend of mine, Christian Legare joined Micriμm Micriµm as Vice President in 2002, and his substantial corporate and technical expertise further accelerated the company’s rapid growth. Since Christian joined MicriμmMicriµm, the company expanded from a one-product company to one with a portfolio of 15 products.
Meanwhile, new features were added to satisfy the ever-evolving needs of μCµC/OS-II users, including a variety of new API functions to the operating system and expanding the maximum number of tasks supported by the kernel from 64 to 255.
As Micriμm’s Micriµm’s president, I remain dedicated to writing world-class kernel code, most recently μCµC/OS-III. The product of countless hours of meticulous programming and testing, this robust operating system has its roots in μCµC/OS-II, yet is an entirely new kernel. Addressing input received from customers and all of the lessons learned along the way, several additional important μCµC/OS-III features were included (see Introduction).
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This philosophy has yielded considerable success. MicriμmMicriµm, now in its 14th year, is a highly respected embedded software provider. Industry surveys consistently show the operating systems to be among the most popular in the embedded space. My goal has always been, and continues to be to provide effective solutions for the same types of problems that I confronted at Dynalco, and that millions of embedded systems developers continue to face today.
Acknowledgements
First and foremost, I’d like to thank my loving and caring wife Manon for her unconditional support, encouragement, understanding and patience. This new book and μC/OS-III software was project was again a huge undertaking, and I could not have done it without her.
I would also like to thank many fine people at Micriμm Micriµm who have tested the code and reviewed the bookdocumentation. In alphabetic order:
- Brian Nagel
- Eric Shufro
- Hong Soong
- Freddy Torres
A special thanks to Frank Voorburg from Feaser and to Ian Hall and Robert Mongrain from Renesas for feedback and corrections to the book, to Michael text to Michael Barr for sharing his real life RTOS experiences, and to Carolyn Mathas for the incredible job of editing this huge project.
A very special thanks to my long-time friend, colleague and partner, Christian Legare, who has provided his advice and support throughout this project and on a day-to-day basis at Micrium. Thank you also to the dozens of people who provided feedback about the μCµC/OS-III code, as well as reviewers of the book.
Finally, I listen to music when I write software, and artist Gino Vannelli’s awesome music has provided a creative environment for me for over three decades. I would be remiss if I did not acknowledge his contribution here as well.
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