Chapter 1PreambleThe guiding principle in the teaching and research agenda related to embedded sys-tems is bringing closer together system theory and computer science. The two fieldshave drifted apart for years while we believe that the core of embedded systemsintended as an engineering discipline lies in the marriage of the two approaches.While computer science traditionally deals with abstractions where the physicalworld has been carefully and artfully hidden to facilitate the development of appli-cation software, system theory deals with the physical foundations of engineeringwhere quantities such as time, power and size play a fundamental role in the modelsupon which this theory is based. The issue then is how to harmonize the physicalview of systems with the abstractions that have been so useful in developing the CSintellectual agenda. We argue that a novel system theory is needed that at the sametime is computational and physical. The basis of this theory cannot be but a set ofnovel abstractions that partially expose the physical reality to the higher levels andmethods to manipulate the abstractions and link them in a coherent whole. Theresearch community is indeed developing some of the necessary results to build thisnovel system theory. We believe it is time to inject these findings in the teachinginfrastructure so that students can be exposed to this new way of thinking. By thesame token, the practitioners should also be exposed to these results that advancethe state of embedded system design to a point where reliable and secure distributedsystems can be designed quickly, inexpensively and with no errors.This book is intended to cover the fundamentals of embedded system design asthey have been developed over the years by the research and industrial community.Being exhaustive is certainly impossible given the many important contributionsand the many industrial and scientific domains the field includes. We chose tofollow an organization for the contents of the book that stems out of a methodology,Platform-Based Design, that has been proposed in various forms by several peopleand that seems to apply well to a wide variety of design problems.The organization of the book reflects the organization of a graduate course,EE249, Embedded System Design: Modeling, Analysis and Synthesis. In US Uni-versities, bottom-up aggregation of interests and approaches to education is morecommon than top-down planning. Hence, education initiatives in novel areas almostalways start with advanced graduate course offerings to migrate towards coordinatedgraduate programs and eventually into undergraduate courses. Thus, it is no won-der that course offering in Berkeley on embedded systems has been strong for yearsin the advanced course series (the EE and CS 290 series) that are related to facultyresearch activities. EE249 indeed started more than ten years ago as an advanced78 CHAPTER 1. PREAMBLEcourse and then migrated in 1998 to a regular offering in the graduate program. Inthese past ten years, the research area and the course contents have solidified to apoint that we feel confident could be used at both the graduate and junior/seniorlevel. For this reason, we mark sections that in our opinion would be best coveredin a graduate course and left out in an undergraduate course.While the book has been designed having in mind its adoption as a textbook,we feel that it could be used as a reference book for practicing engineers as well.We would like to acknowledge the support of our families, friends and colleaguesduring the writing of this book. A special thank you goes to students who tookEE249 and to the ones who helped teaching the class.Chapter 2IntroductionThis book is about the principles of system level design. System-Level Design (SLD)means many different things to many different people. In our view, system-leveldesign is about the design of a whole by assembling components where specificationsare given in terms of functionality (what the system is supposed to do; for example,a brake-by-wire automotive controller must actuate the braking action activated bythe driver so that the wheels never lock) with:• constraints on the properties the design has to satisfy, (for the brake-by-wirecontroller, the braking action must be stable), and on the components, (forthe same example, the embedded micro-controller used in the implementationmust be more reliable than a given threshold) and• objective functions that express the desirable features of the design whencompleted (for example, low overall manufacturing cost of the controller).This definition is general since it relates to many different application domains, fromsemiconductors to systems such as cars and airplanes, buildings, telecommunicationand biological systems. In this book, we focus on a particular, but very wide area,embedded system design.With the term embedded systems we refer to the electronic components (whichalmost always include one or more software programmable parts) of a wide varietyof personal or broad-use devices, e.g., a mechanical system such as an automobile,a train, a plane, an electrical system such as an electrical motor or generator, achemical system such as a distillation plant, a health-care equipment such as apace-maker. Hence, an embedded system is a special-purpose system in which thecomputing element is completely encapsulated by the device it controls. “Unlike ageneral-purpose computer, an embedded system performs one or a few pre-definedtasks, usually with very specific requirements” [110]. In technical terms, an em-bedded system interacts with the surrounding environment in a controlled waysatisfying a set of requirements on responsiveness in terms of quality and timeli-ness. Typically it has to satisfy implementation requirements such as cost, powerconsumed, and use of limited physical resources. Ideally its interaction with theenvironment should be continuously available for the entire life of the artifact.Design tools have been important to deliver exponential increase in integratedcircuit complexity with much improved designers’ productivity. An entire industry,the Electronic Design Automation (EDA) industry, reached maturity in the 1980s.EDA today offers a rich tool set and flows for IC and board design. The samelevel of maturity has not been reached in the embedded system design tool domain.910 CHAPTER 2. INTRODUCTIONThere are some notable companies in the space, e.g., the Mathworks, but an
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