Introduction. zwhat are embedded systems? zchallenges in embedded computing system design. zdesign methodologies Morgan Kaufman

Transcription

1 Introduction zwhat are embedded systems? zchallenges in embedded computing system design. zdesign methodologies.

2 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.

3 Embedding a computer output analog CPU input analog embedded computer mem

4 Examples zpersonal digital assistant (PDA). zprinter. zcell phone. zautomobile: engine, brakes, dash, etc. ztelevision. zhousehold appliances. zpc keyboard (scans keys).

5 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.

6 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.

7 Microprocessor varieties zmicrocontroller: includes I/O devices, onboard memory. zdigital signal processor (DSP): microprocessor optimized for digital signal processing. ztypical embedded word sizes: 8-bit, 16- bit, 32-bit.

8 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.

9 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.

10 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.

11 BMW 850i, cont d. sensor sensor brake brake ABS hydraulic pump brake brake sensor sensor

12 Characteristics of embedded systems zsophisticated functionality. zreal-time operation. zlow manufacturing cost. zlow power. zdesigned to tight deadlines by small teams.

13 Functional complexity zoften have to run sophisticated algorithms or multiple algorithms. ycell phone, laser printer. zoften provide sophisticated user interfaces.

14 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.

15 Non-functional requirements zmany embedded systems are massmarket items that must have low manufacturing costs. ylimited memory, microprocessor power, etc. zpower consumption is critical in batterypowered devices. yexcessive power consumption increases system cost even in wall-powered devices.

16 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.

17 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.

18 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.

19 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.

20 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?

21 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?

22 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.

23 Design goals zperformance. yoverall speed, deadlines. zfunctionality and user interface. zmanufacturing cost. zpower consumption. zother requirements (physical size, etc.)

24 Levels of abstraction requirements specification architecture component design system integration

25 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.

26 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.

27 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.

28 Functional vs. nonfunctional requirements zfunctional requirements: youtput as a function of input. znon-functional requirements: ytime required to compute output; ysize, weight, etc.; ypower consumption; yreliability; yetc.

29 Our requirements form name purpose inputs outputs functions performance manufacturing cost power physical size/weight

30 E x Scotch Road requirements zmoving map obtains position from GPS, paints map from local database. I-78 lat: lon: 32 19

31 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.

32 GPS moving map needs, cont d. zphysical size/weight: Should fit in dashboard. zpower consumption: Current draw comparable to CD player.

33 GPS moving map requirements form name GPS moving map purpose consumer-grade moving map for driving inputs power button, two control buttons outputs back-lit LCD 400 X 600 functions 5-receiver GPS; three resolutions; displays current lat/lon performance updates screen within 0.25 sec of movement manufacturing cost $100 cost-of-goodssold power 100 mw physical size/weight no more than 2: X 6:, 12 oz.

34 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.

35 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.

36 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.

37 GPS moving map block diagram GPS receiver search engine renderer display database user interface

38 GPS moving map hardware architecture display frame buffer memory CPU GPS receiver panel I/O

39 GPS moving map software architecture position database search renderer pixels user interface timer

40 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.

41 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.

42 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.