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Embedded SystemsIntroduction

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What is an Embedded System?

q Definition of an embedded computer system:s is a digital system.

s uses a microprocessor (usually).

s runs software for some or all of its functions.

s frequently used as a controller.

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What an embedded system isNOT.

q Not a computer system that is used primarily forprocessing.

q Not a software system on a PC or Unix box.

q Not a traditional business or scientific application.

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Examples of EmbeddedSystems

Automotive systems:electronic

dashboards, ABS brakes,transmission controls.

Medical instrumentscontrols:CAT scanners, implantedheart

monitors, etc.

Controls for digital equipment: CD players, TV remote,programmable sprinklers, household appliances, etc.

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Why embedded?

q Because the processor is inside some othersystem.

q A microprocessor is embedded into your TV, car,or appliance.

q The consumer does not think about performingprocessing,

q Considers running a machine or `makingsomething work.

q Considered part of the thing rather than thething

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Special Characteristics

hardware and software (in one system)

sensors andactuators(for inputsand outputs)

synchronization (this processmust complete before thisprocess begins)

timing(often realtime)

concurrency (several

processes working atsame time)

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Timing and Concurrency

Engine

shaft angle

Fire Injectors

Fire Spark

Watch

Emissions

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How are embedded systems differentthan traditional software?

q Responding to sensors (Was this buttonpushed?)

q Turning on actuators (Turn on power to theboiler.)

q Real-time (Respond to temperature change

within 3 seconds.)

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Differences between ES and traditionalsoftware development

q Not dealing with only sequential code.

q Routine can stop at completion or in response toan external event.

q Many parts of system might be runningconcurrently.

q Safety-critical component of many systems.

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Small and Many!

q Most embedded systems use 4-, 8-, or 16-bit processors.32-bit used for intensive applications like printer controls.

q 8-bit processors have about 64K of memory, that limitsamount of code.

q By 1990 a total of about 45 million recognizable computers (i.e., PCs,Macintosh, even CP/M systems) were in place. Yet over 1 billionmicroprocessors and microcontrollers were shipped in that yearalone!

Ganssle, J. The Art of Programming Embedded Systems Academic Press, 1992, San Diego, Cal.

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hardware or

?

q Where to place functionality?

s ex: A Sort algorithm

x Faster in hardware, but more expensive.

x More flexible in software but slower.

x Other examples?

q Must be able to explore these various trade-offs:

s Cost.

s Speed.

s Reliability.

s Form (size, weight, and power constraints.)

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hardware/software Codesign or

Codesign

q Model the hardware and the software system in aunified approach.

q Use similar design models.

q Need for model continuity spanning levels of thedesign process.

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Traditional Embedded SystemDevelopment Approach

q Decide on the hardwareq Give the chip to the software people.

q Software programmer must make software fit onthe chip and only use that hardwares capabilities.

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Increased Complexity

q Systems are becoming more and more complex.q Harder to think about total design.

q Harder to fix bugs.

q Harder to maintain systems over time.

q Therefore, the traditional development processhas to change,

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Less Time to Develop

q In embedded electronics, the total design cycle must

decrease.

q Historically, design for automotive electronic systems

takes 3-5 years to develop.

q Must become a 1-3 year development cycle.

q Must still be reliable and safe.B. Wilkie, R. Frank and J. Suchyta - Motorola Semiconductor Products Sectors, Silicon or Software: The Foundation of

Automotive Electronics, IEEE Vehicular Tech., August 95.

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Solutions to Complexity:

q Need to keep design process abstract for a longerperiod of time.

q Decomposable hierarchy (object-oriented).

q Reuse previous designs:s When a design changes, reuse similar sections.

s Dont throw away last years design and start from scratch!

q Automated verification systems.

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Example: Fly-by-Wire Airplane

q How would you start to think about developing thiscomplex/large system?

q What are potential problems with deciding on thehardware right away?

q What are possible concurrent systems needs?

q What type of timing constraints might be needed?

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Fly-by-Wire AirplaneContinued

q What would be the sensors and actuators of thissystem?

q How concerned should developers be about thesafety of the system?

q Would testing be enough?