What Is Embedded Computing?

more stringent cost and power con- straints. PDA design requires careful What Is Embedded attention to both hardware and software. In the next decade, some microprocessors, largely invisible to users, Computing? will be used for signal processing and control—for example, to enable home Wayne Wolf, Princeton University networking across noisy, low-quality media such as power lines. Others will be used to create advanced user inter-

or those who think a lot about embedded computing, as well as Evolving from a craft to an the uninitiated, it’s important to engineering discipline over F define exactly what the term means. In brief, an embedded the past decade, embedded system is any computer that is a com- ponent in a larger system and that relies computing continues to on its own microprocessor. mature. But is embedded computing a field or just a fad? The purpose of this new bimonthly column is to give researchers difficult to implement in mechanical faces—for example, for the entire clus- as well as practitioners an opportunity controllers. ter of home entertainment devices. to demonstrate that embedded com- Laser and inkjet printers also Microprocessors have also enabled puting is an established engineering dis- emerged in the 1980s. Print engines new categories of portable devices cipline with principles and knowledge require computational support for that will assume roles and perform at its core. both typesetting and real-time control. functions yet to be determined. The First, users generate characters and cell phone and PDA combinations A LONG HISTORY lines that a computation must convert that hit the market in 2001 are a People have been building embedded into pixels. Translating page descrip- major step in the evolution of hand- systems—including complex systems— tion languages requires executing a held devices. As third-generation for decades. The early microprocessors great deal of code that performs a wide communication systems deploy, wire- were so limited that calling what they range of functions. Second, the pixels less networks will incorporate multi- did “computing” is generous; their pri- must be delivered to the printer at just media—many cell phones used in mary function was to manage input- the right moment; this is particularly Japan already have large screens and output devices, and squeezing per- true of inkjets. cameras, and wireless handsets will formance out of these systems required Cell phones use coprocessors for soon feature video. more craft than science. digital-signal processing and micro- By the early 1980s, however, design- processors for button control and pro- AN EMERGING FIELD ers were using 16-bit microprocessors tocol processing. By the early 1990s, a Although we all use embedded to create very sophisticated applica- typical cell phone contained five or six devices on a daily basis, should embed- tions. One example is the 68000, DSPs and CPUs. The telephone infra- ded computing have the status of a sep- which car designers used to build auto- structure also uses embedded DSPs and arate discipline such as integrated mobile engine controls that relied on microprocessors extensively. engineering or software management? sophisticated algorithms to manage The answer is a resounding yes. fuel and spark. Using the 68000’s com- NEW APPLICATIONS Already central to most electronic putational power improved fuel effi- Products ranging from the multibil- systems, embedded computers perform ciency and reduced emissions while lion-dollar B-2 bomber to home appli- increasingly numerous functions that making the engine easier to start in var- ances or one-dollar novelties now rely once would have been implemented in ious environments. Some car design on embedded computers. Personal dig- random logic and that require many algorithms used numerical methods ital assistants must support devices, algorithms too complex to build in like Kalman filters; others were more operating systems, and user-loaded hardwired logic. Embedded computer complex and used multiple modes too applications, just like PCs, but with hardware and software are on the crit-

136 Computer ical design path for many types of elec- achieve those goals. Embedded com- Verification tronic systems. puting has five primary objectives. Embedded system designs must meet It’s tempting to believe that adding their functional specifications as well CPUs makes it easier to design and Architectural design as nonfunctional specs such as speed change a system, but the opposite is Embedded computing seeks to design and power consumption. Hardware- true. Any number of problems in an architectures that can execute a partic- software cosimulation tools developed embedded computing system can result ular application’s functions—protocols, in the 1990s can simulate systems at in disaster. For example, signal processing, user interface, and so multiple levels of abstraction, which on—while meeting all performance and greatly speeds up simulation through- • using an undersized hardware power requirements. The theoretical put. However, we need more advanced platform causes software design formal methods to complement simu- difficulties; lation. • bad software architecture can lead Embedded computer to software, performance, and hardware and software Application orientation power problems; and are on the critical design Developing architectures for com- • underestimating power consump- path for many types mon applications—wireless, video, tion can reduce the entire system’s of electronic systems. networking, and so on—is another effective lifetime. function of embedded computing. This involves adjusting to design tradeoffs Software design is always challeng- basis for custom software architectures that result from the ability to fit more ing, particularly when it needs to meet evolved with real-time systems theory processing power onto a single chip. performance and power requirements in the 1970s; during the past decade, Also, knowing just what state-of-the- as well as achieve functional correct- hardware-software codesign developed art technology is can be difficult ness. In addition, programmability cre- design algorithms. because developers often do not dis- ates a temptation that entices designers close novel designs until long after they to write ever more complex specifica- Analysis create them. We are making substan- tions. As our ability to fabricate and Embedded system designers also tial progress in understanding the basic design complex systems improves, the strive to characterize both hardware shape of architectures suitable for goal posts keep moving—we must per- and software for performance, power, many of the major application areas in form better just to stay even. and size. This goal is clearly related to embedded computing. Without techniques to reliably bring the first—we can’t design an architec- complex embedded systems to fruition, ture until we understand the compo- on time and on budget, we face prob- nents’ characteristics. Much progress his column will consider both the lems keeping pace with very large-scale has been made in the last decade on var- diversity and unity of embedded integration. In conformance with ious aspects of measurement including T computing in hardware, software, Moore’s law, advances in VLSI manu- timing analysis of embedded software and applications. We’ll look at partic- facturing over the next decade will and power analysis of architectures. ular domains—control, communica- require using embedded computers to tions, and so on—to discuss the build huge chips. Modeling problems that embedded system An embedded CPU is a predesigned To analyze embedded systems at an designers encounter, but we’ll also step block of intellectual property that can appropriate level of abstraction, back and examine broader principles. be reused many times. Embedded CPUs designers must create a hierarchy of I have my own opinions on embed- require memory, another reusable IP models. For example, analyzing a ded computing, but various guest block. This reusability facilitates design microprocessor’s power consumption columnists from both industry and management, making it possible to at entirely at the gate level—assuming the academia will also share their exper- least partly decouple hardware and soft- manufacturer provides the gate-level tise in this column. I look forward to ware designs. If they can characterize IP design—is less desirable than having engaging in a dialogue with you in block performance and understand IP an abstract model that relates to the future issues of Computer. interactions, software designers can use behavior of the programs running on IP blocks as their models. the microprocessor. Researchers are making progress in understanding how Wayne Wolf is a professor of electrical GOALS to analyze a program without going engineering at Princeton University A field is defined by its goals and down to the instruction level, but more and CTO of MediaWorks Technology. matures as it articulates ways to work remains to be done. Contact him at [email protected].

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