UML for Real: Design of Embedded Real-Time Systems

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The Unified Modelling Language (UML)

Since the second half of the s asynchronous circuits have been the subject of a great deal of research following a period of relative oblivion. The lack of interest in asynchronous techniques was motivated by the progressive shift towards synchronous View Product. Analysis and Design of Structural Bonded Joints. Condensed Systems of Low Dimensionality.

Design Considerations of Time in Fuzzy Systems. Fuzzy theory is an interesting name for a method that has been highly effective in Fuzzy theory is an interesting name for a method that has been highly effective in a wide variety of significant, real-world applications. A few examples make this readily apparent. As the result of a faulty design the method of computer-programmed Embedded System Applications.

Embedded systems encompass a variety of hardware and software components which perform specific functions in Embedded systems encompass a variety of hardware and software components which perform specific functions in host systems, for example, satellites, washing machines, hand-held telephones and automobiles.

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Embedded systems have become increasingly digital with a non-digital periphery analog power and therefore, Real-time computer systems are very often subject to dependability requirements because of their application areas. Fly-by-wire airplane control systems, control of power plants, industrial process control systems and others are required to continue their function despite faults.

Table of Contents

Fault-tolerance and real-time Intelligent Systems: Concepts and Applications. Drawing from the fields of pattern Martin on Pulsed Power. As indicated in the Foreword to this series on Advances in Pulsed Power Technologies, the pioneering roots of modern pulsed power as related by J. What about the real-time profiles? There's a document called "UML Profile for Modeling Quality of Service and Fault Tolerant Characteristics and Mechanisms" that defines stereotypes for properties such as performance, dependability, security, integrity, coherence temporal consistency of data and software elements , throughput, latency, efficiency, demand, reliability, and availability.

Throughput, for example, defines stereotypes "input-data-throughput," "communication-throughput," and "processing-throughput. My favorite here is "ThreatAgent," which can be denoted by a stick-figure icon holding a bomb. You can decorate your model from this catalog of icons and properties to define the real-time requirements of your application problem.

Tools may then use this information to construct implementations, though at present this is not directly possible. Consider a class with a "communication-throughput" value over some "observationInterval. There are many ways of realizing this requirement; tools are not yet able to decide between them. Nonetheless, having a standard set of concepts defined for characterizing real-time systems is valuable.

UML for Real: Design of Embedded Real-Time Systems

Each tool set defines one member of the family. Different tools exist because each tool serves a different subset of the market; even so, all tools are pretty much based on the UML standard. What you look for depends on how you want to go about developing systems using UML. If you intended to use it as a sketching language, your requirements will be quite different from what you look for if you want execution.

There's no substitute for doing the research, especially as tools grow and change over time. Does this mean I have to have an agreed development process to use UML? You need to have an agreed development process, with or without UML, if you're going to work together as a team. Working as team doesn't require a "heavyweight" process, however; you could all decide that your process is as simple as "Talk to customer, write code, test it, feedback to customer.

But doesn't UML define the process? If two people Amy and Bob were working together, and Amy builds models in this order: use cases, sequence diagrams, code, and Bob builds class diagrams, state machine diagrams, then actions, Amy and Bob would not be able to communicate as effectively as if their processes had some commonality. Bringing UML into a project is sometimes cast as an answer to the question, "How do we build software? Using UML doesn't have to change your development process, but the introduction of UML is often seen as an opportunity to make some changes.

It's critical for your success that you consider what you want your process to be and then make your use of UML fit that process. Do you have a preferred process for real-time systems? I prefer to build executable models consisting of class diagrams and state-machine diagrams for those classes, and then write action language for the state machines. All of the processing in the system is housed in concurrently executing state machine instances, which helps capture concurrency in the application so it can be mapped into an implementation.

I didn't see use cases. Why not? Use cases in UML are remarkably popular, and with good reason: they help focus our attention on the requirements and not on the coding. Especially in real-time systems, with our hard-to-meet time and memory constraints, it's all too easy to fall into designing the system before acquiring an understanding of the problem. This is where use cases can help. Use cases help us build executable and translatable models, but they do not themselves execute.

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What do you mean by "translatable"? An executable model can be interpreted, but that is unlikely to yield a system that meets performance constraints. Accordingly, the model must be translated into an implementation using a set of formalized rules that, for example, take a class and turn it into a C struct, a state-machine diagram, and a set of switch statements, or take a CreateObjectAction and turn it into a malloc , and so on. Each set of rules must be internally self-consistent, and a complete set is called a model compiler. What's a model compiler? A model compiler is simply a set of rules that read a developer's model as captured in a metamodel and turn it into text.

That text, of course, will often be consistent with programming language syntax in other words, the text is a C program , that can itself be compiled onto a processor. How does a model compiler differ from a programming-language compiler? Model compilers aren't significantly different from traditional compilers. It's just that the level of abstraction in the UML "programming language" is higher, so much so that the UML program is independent of its platform.

Real-Time Systems UML Training Courses and Workshops

You don't even need to make decisions about data structures. A model compiler, is, in fact, exactly analogous to a programming language compiler but at a higher level of abstraction. Why exactly is UML at a "higher level of abstraction? On a different processor, it may do something altogether different.

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C has "abstracted away" the details of register allocation and even the concept of if, turning it into GOTOs jump or branch instructions we would normally eschew. When we write in UML that two classes have an association between them, we have abstracted away how the association is made. We don't say whether the implementation uses a linked list, a doubly-linked list, or a table--just as we don't say anything about registers when we write C.

In blueprint-style UML, you abstract away details like this but there is still a nearly one-to-one correlation between the model and the code. In executable UML, we go further and abstract away all data structure decisions, tasking structure decisions, and language decisions and leave these to the model compiler.

How many model compilers are there? That's like asking, "How many possible designs are there for the same problem? The answer is that there's one model compiler for each possible design; related designs may be housed in the same package using compiler switches. For example, we use a Java model compiler to build our own UML toolset, which is itself modeled.

We offer a small-footprint C-based model compiler for real-time and embedded systems. Are the market leaders ready for model compilers?

Whether the leaders of the market are ready to adopt executable UML is a chicken-and-egg problem. Vendors won't build a solution until they see a market, and customers won't buy tools until they see them available. Even a well-proven tool such as Accelerated Technology's BridgePoint, which has been in the market for 10 years now, can be perceived as risky until further standards are developed.

But we already have another standard UML! Why do we need a standard? Executable UML relies on a subset of UML, but each vendor could choose a different subset on which to base its model compilers. That would reduce interoperability. Moreover, the execution semantics of UML are not formally defined. When can we expect that standard from the OMG? Should I wait, then? How visible should my shiny new UML project be? UML doesn't guarantee success, which, obviously enough, admits of the possibility of failure.

In other words, it's a gamble. You have to decide how much you're willing to risk before you see how the project will turn out. Most engineers instinctively go for the low-risk approach, choosing a low-visibility project or a low-visibility piece of an important project.

Of course with low risks, the rewards are lame as well. The investment, and therefore the risk, is less for sketching than for executable modeling. Consequently, it matters less how visible your project is. Equally, executable models give you the most return on your investment but visibilty matters more. The same applies for the headings that follow. How big should my first project be? Adopting any new technology on a wide scale, all at once, is rarely a good idea.

Pick a project that's manageable in size. It has to be big enough to matter but small enough that you can steer it. Don't underestimate the force required to overcome organizational inertia. What kind of application is best for a first project? Don't pick a project that's basically algorithmic. Mathematics is a perfectly good "modeling language" for much of that. UML really helps in laying out the overall structure of an application and is particularly well suited for understanding concurrent behavior.

So look for something that's complex enough in the control aspect that your best programmer would struggle to sort it out. Got concurrency? Model it. What about legacy code? If you have lots of legacy code you may spend more time trying to interface the newly generated code to it than it's worth. Pick an initial project where the return-on-investment for learning a new technology is high enough to matter. How well should I know my application? Should I start with something new? Start by modeling something you know really well. Don't try to learn a new subject matter or push the envelope of one you already know while you're learning to model.

After you're comfortable modeling, use your new skills to explore more-complex and unfamiliar areas where you can get a greater return on the investment. What kind of people should I get? You'll need smart people, and you'll need several different skill sets along with that intelligence. More important than talent and wit is desire. There's no better way to ensure failure than to populate the project with a few folks who don't believe this new-fangled approach can work for their problem.

We never get to do anything that's ideal, so we end up making tradeoffs between the desired project and what's available. Only you can make these tradeoffs. In some situations it's better to have a small, nearly invisible success than to risk a spectacular failure. In other cases, it might be just the reverse, where having success in a low-risk environment could just confirm for some that UML is not serious. In the end, indecision is worse than failure. Pick a project, staff it with people, and then make it work. For some help in making the decision to proceed, take a look at the brief self-assessment below.

Self-assessment This self-assessment is divided into several sections. The first question is, where does it hurt? The more of these problems you have, the more helpful the sketching capabilities of UML will be. If so, the additional capabilities offered by code-frame generation in blueprint-style UML diagrams, will help. These pain points call for using executable UML for separate reuse of the application and design, as well as executing the application early. Blueprints and sketches in UML will not help with this pain. Now let's move on to some conditions.

How attached are you and your team to code? In these last two questions, if you answered yes to the first bullet point under both questions, sketching is for you; answering yes to the second bullet points calls for blueprints, and yes to the third bullet points indicates executable models are what you need. Know thyself When considering moving to UML, you must consider what you hope to get out of it.

If you're looking for visualization of software structure, low investment, and very low risk, using UML informally as a sketching language is for you. If you're looking to specify systems using UML, you will need to invest more in learning the language and in tools to support it. You'll need to think carefully about your process, especially for any team effort. If you're looking to reuse either the models or the implementation, you need fewer defects, and the ability to optimize globally, executable models is the way to go.

Mellor is an internationally recognized pioneer in creating effective, engineering approaches to software development. In , he published the widely read Ward-Mellor trilogy Structured Development for Real-Time Systems , and in , the first books defining object-oriented analysis. He is a signatory to the Agile Manifesto.

Stephen co-founded a company focused on tools to execute and translate UML models. Acknowledgments: The format of this article and some questions were inspired by Pierrick Arlot, who published an interview with me in Electronique International. The team at Accelerated Technology provided some of the questions in the self-assessment.

Endnotes: 1. Fowler, Martin. Boston, MA : Addison-Wesley, Douglass, Bruce Powel. Reading, Mass.

Balcer, Marc and Stephen Mellor. Boston; San Francisco; New York: 5. Venture Data Corporation. Agile Alliance: www. Beck, Kent. Mellor, Stephen. Arlot, Pierrick. I've read a couple of books on UML, but until I read this article, I didn't see how it applied to embedded design. Thanks for enlightening me to an application of what I thought was otherwise non-applicable. Specifically something free I can download and try out, and thus share with the team. There are many open source UML projects out there. What do you recommend trying?

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UML for Real: Design of Embedded Real-Time Systems UML for Real: Design of Embedded Real-Time Systems
UML for Real: Design of Embedded Real-Time Systems UML for Real: Design of Embedded Real-Time Systems
UML for Real: Design of Embedded Real-Time Systems UML for Real: Design of Embedded Real-Time Systems
UML for Real: Design of Embedded Real-Time Systems UML for Real: Design of Embedded Real-Time Systems
UML for Real: Design of Embedded Real-Time Systems UML for Real: Design of Embedded Real-Time Systems
UML for Real: Design of Embedded Real-Time Systems UML for Real: Design of Embedded Real-Time Systems
UML for Real: Design of Embedded Real-Time Systems UML for Real: Design of Embedded Real-Time Systems

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