What are embedded systems? Challenges in embedded ...
Transcript of What are embedded systems? Challenges in embedded ...
© 2000 Morgan Kaufman
Overheads for Computers as Components
Introduction
zWhat are embedded systems?zChallenges in embedded computing
system design.zDesign methodologies.
© 2000 Morgan Kaufman
Overheads for Computers as Components
Definition
zEmbedded system: any device that includes a programmable computer but is not itself a general-purpose computer.zTake advantage of application
characteristics to optimize the design:ydon’t need all the general-purpose bells and
whistles.
© 2000 Morgan Kaufman
Overheads for Computers as Components
Embedding a computer
CPU
mem
input
output analog
analog
embeddedcomputer
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Examples
zPersonal digital assistant (PDA).zPrinter.zCell phone.zAutomobile: engine, brakes, dash, etc.zTelevision.zHousehold appliances.zPC keyboard (scans keys).
© 2000 Morgan Kaufman
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Early history
zLate 1940’s: MIT Whirlwind computer was designed for real-time operations.yOriginally designed to control an aircraft
simulator.
zFirst microprocessor was Intel 4004 in early 1970’s.zHP-35 calculator used several chips to
implement a microprocessor in 1972.
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Early history, cont’d.
zAutomobiles used microprocessor-based engine controllers starting in 1970’s.yControl fuel/air mixture, engine timing, etc.yMultiple modes of operation: warm-up,
cruise, hill climbing, etc.yProvides lower emissions, better fuel
efficiency.
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Microprocessor varieties
zMicrocontroller: includes I/O devices, on-board memory.zDigital signal processor (DSP):
microprocessor optimized for digital signal processing.zTypical embedded word sizes: 8-bit, 16-
bit, 32-bit.
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Application examples
zSimple control: front panel of microwave oven, etc.zCanon EOS 3 has three microprocessors.y32-bit RISC CPU runs autofocus and eye
control systems.
zAnalog TV: channel selection, etc.zDigital TV: programmable CPUs +
hardwired logic.
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Automotive embedded systems
zToday’s high-end automobile may have 100 microprocessors:y4-bit microcontroller checks seat belt;ymicrocontrollers run dashboard devices;y16/32-bit microprocessor controls engine.
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BMW 850i brake and stability control system
zAnti-lock brake system (ABS): pumps brakes to reduce skidding.zAutomatic stability control (ASC+T):
controls engine to improve stability.zABS and ASC+T communicate.yABS was introduced first---needed to
interface to existing ABS module.
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BMW 850i, cont’d.
brake
sensor
brake
sensor
brake
sensor
brake
sensor
ABS hydraulicpump
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Characteristics of embedded systems
zSophisticated functionality.zReal-time operation.zLow manufacturing cost.zLow power.zDesigned to tight deadlines by small
teams.
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Functional complexity
zOften have to run sophisticated algorithms or multiple algorithms.yCell phone, laser printer.
zOften provide sophisticated user interfaces.
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Real-time operation
zMust finish operations by deadlines.yHard real time: missing deadline causes
failure.ySoft real time: missing deadline results in
degraded performance.
zMany systems are multi-rate: must handle operations at widely varying rates.
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Non-functional requirements
zMany embedded systems are mass-market items that must have low manufacturing costs.yLimited memory, microprocessor power, etc.
zPower consumption is critical in battery-powered devices.yExcessive power consumption increases
system cost even in wall-powered devices.
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Design teams
zOften designed by a small team of designers.zOften must meet tight deadlines.y6 month market window is common.yCan’t miss back-to-school window for
calculator.
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Why use microprocessors?
zAlternatives: field-programmable gate arrays (FPGAs), custom logic, etc.zMicroprocessors are often very efficient:
can use same logic to perform many different functions.zMicroprocessors simplify the design of
families of products.
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The performance paradox
zMicroprocessors use much more logic to implement a function than does custom logic.zBut microprocessors are often at least as
fast:yheavily pipelined;ylarge design teams;yaggressive VLSI technology.
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Power
zCustom logic is a clear winner for low power devices.zModern microprocessors offer features to
help control power consumption.zSoftware design techniques can help
reduce power consumption.
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Challenges in embedded system design
zHow much hardware do we need?yHow big is the CPU? Memory?
zHow do we meet our deadlines?yFaster hardware or cleverer software?
zHow do we minimize power?yTurn off unnecessary logic? Reduce memory
accesses?
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Challenges, etc.
zDoes it really work?yIs the specification correct?yDoes the implementation meet the spec?yHow do we test for real-time characteristics?yHow do we test on real data?
zHow do we work on the system?yObservability, controllability?yWhat is our development platform?
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Design methodologies
zA procedure for designing a system.zUnderstanding your methodology helps
you ensure you didn’t skip anything.zCompilers, software engineering tools,
computer-aided design (CAD) tools, etc., can be used to:yhelp automate methodology steps;ykeep track of the methodology itself.
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Design goals
zPerformance.yOverall speed, deadlines.
zFunctionality and user interface.zManufacturing cost.zPower consumption.zOther requirements (physical size, etc.)
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Levels of abstraction
requirements
specification
architecture
componentdesign
systemintegration
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Top-down vs. bottom-up
zTop-down design:ystart from most abstract description;ywork to most detailed.
zBottom-up design:ywork from small components to big system.
zReal design uses both techniques.
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Stepwise refinement
zAt each level of abstraction, we must:yanalyze the design to determine
characteristics of the current state of the design;yrefine the design to add detail.
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Requirements
zPlain language description of what the user wants and expects to get.zMay be developed in several ways:ytalking directly to customers;ytalking to marketing representatives;yproviding prototypes to users for comment.
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Functional vs. non-functional requirements
zFunctional requirements:youtput as a function of input.
zNon-functional requirements:ytime required to compute output;ysize, weight, etc.;ypower consumption;yreliability;yetc.
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Our requirements form
namepurposeinputsoutputsfunctionsperformancemanufacturing costpowerphysical size/weight
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E xample: GPS moving map
requirements
zMoving map obtains position from GPS, paints map from local database.
lat: 40 13 lon: 32 19
I-78
Scotch Road
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GPS moving map needs
zFunctionality: For automotive use. Show major roads and landmarks.zUser interface: At least 400 x 600 pixel
screen. Three buttons max. Pop-up menu.zPerformance: Map should scroll smoothly.
No more than 1 sec power-up. Lock onto GPS within 15 seconds.zCost: $500 street price = approx. $100
cost of goods sold.
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GPS moving map needs, cont’d.
zPhysical size/weight: Should fit in dashboard.zPower consumption: Current draw
comparable to CD player.
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GPS moving map requirements form
name GPS moving mappurpose consumer-grade
moving map for drivinginputs power button, two
control buttonsoutputs back-lit LCD 400 X 600functions 5-receiver GPS; three
resolutions; displayscurrent lat/lon
performance updates screen within0.25 sec of movement
manufacturing cost $100 cost-of-goods-sold
power 100 mWphysical size/weight no more than 2: X 6:,
12 oz.
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Specification
zA more precise description of the system:yshould not imply a particular architecture;yprovides input to the architecture design
process.
zMay include functional and non-functional elements.zMay be executable or may be in
mathematical form for proofs.
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GPS specification
zShould include:yWhat is received from GPS;ymap data;yuser interface;yoperations required to satisfy user requests;ybackground operations needed to keep the
system running.
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Architecture design
zWhat major components go satisfying the specification?zHardware components:yCPUs, peripherals, etc.
zSoftware components:ymajor programs and their operations.
zMust take into account functional and non-functional specifications.
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GPS moving map block diagram
GPSreceiver
searchengine renderer
userinterfacedatabase
display
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GPS moving map hardware architecture
GPSreceiver
CPU
panel I/O
display framebuffer
memory
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GPS moving map software architecture
position databasesearch renderer
timeruserinterface
pixels
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Designing hardware and software components
zMust spend time architecting the system before you start coding.zSome components are ready-made, some
can be modified from existing designs, others must be designed from scratch.
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System integration
zPut together the components.yMany bugs appear only at this stage.
zHave a plan for integrating components to uncover bugs quickly, test as much functionality as early as possible.
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Summary
zEmbedded computers are all around us.yMany systems have complex embedded
hardware and software.
zEmbedded systems pose many design challenges: design time, deadlines, power, etc.zDesign methodologies help us manage
the design process.