ch8 - Chapter 8: Computation models Chapter 8 8.1 8-1...

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Chapter 8: Computation models 8-1 Embedded System Design, Vahid/Givargis Last update: 11/19/99 11:25 AM Chapter 8 Computation models 8.1 Introduction We implement a system’s processing behavior with processors. But to accomplish this, we must have first described that processing behavior. One method we’ve discussed for describing processing behavior uses assembly language. Another, more powerful method uses a high-level programming language like C. Both these methods use what is known as a sequential program computation model, in which a set of instructions executes sequentially. A high-level programming language provides more advanced constructs for sequencing among the instructions than does an assembly language, and the instructions are more complex, but nevertheless, the sequential execution model (one statement at a time) is the same. However, embedded system processing behavior is becoming very complex, requiring more advanced computation models to describe that behavior. The increasing complexity results from increasing IC capacity: the more we can put on an IC, the more functionality we want to put into our embedded system. Thus, while embedded systems previously encompassed applications like washing machines and small games requiring perhaps hundreds of lines of code, today they also extend to fairly sophisticated applications like television set-top boxes and digital cameras requiring perhaps hundreds of thousands of lines. Trying to describe the behavior of such systems can be extremely difficult. The desired behavior is often not even fully understood initially. Therefore, designers must spend much time and effort simply understanding and describing the desired behavior of a system, and some studies have found that most system bugs come from mistakes made describing the desired behavior rather than from mistakes in implementing that behavior. The common method today of using an English (or some other natural language) description of desired behavior provides a reasonable first step, but is not nearly sufficient, because English is not precise. Trying to describe a system precisely in English can be an arduous and often futile endeavor -- just look at any legal document for any example of attempting to be precise in a natural language. A computation model assists the designer to understand and describe the behavior by providing a means to compose the behavior from simpler objects. A computation model provides a set of objects, rules for composing those objects, and execution semantics of the composed objects. For example, the sequential program model provides a set of statements, rules for putting statements one after another, and semantics stating how the statements are executed one at a time. Unfortunately, this model is often not enough. Several other models are therefore also used to describe embedded system behavior. These include the communicating process model, which supports description of multiple sequential programs running concurrently. Another model is the state machine
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This note was uploaded on 06/02/2011 for the course CS 550 taught by Professor Young during the Spring '11 term at New York Institute of Technology-Westbury.

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ch8 - Chapter 8: Computation models Chapter 8 8.1 8-1...

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