Introduction z What are embedded systems z Challenges
Introduction z. What are embedded systems? z. Challenges in embedded computing system design. z. Design methodologies. © 2000 Morgan Kaufman Overheads for Computers as Components
Definition z. Embedded system: any device that includes a programmable computer but is not itself a general-purpose computer. z. Take 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 embedded computer © 2000 Morgan Kaufman output analog input analog mem Overheads for Computers as Components
Examples z. Personal digital assistant (PDA). z. Printer. z. Cell phone. z. Automobile: engine, brakes, dash, etc. z. Television. z. Household appliances. z. PC keyboard (scans keys). © 2000 Morgan Kaufman Overheads for Computers as Components
Early history z. Late 1940’s: MIT Whirlwind computer was designed for real-time operations. y. Originally designed to control an aircraft simulator. z. First microprocessor was Intel 4004 in early 1970’s. z. HP-35 calculator used several chips to implement a microprocessor in 1972. © 2000 Morgan Kaufman Overheads for Computers as Components
Early history, cont’d. z. Automobiles used microprocessor-based engine controllers starting in 1970’s. y. Control fuel/air mixture, engine timing, etc. y. Multiple modes of operation: warm-up, cruise, hill climbing, etc. y. Provides lower emissions, better fuel efficiency. © 2000 Morgan Kaufman Overheads for Computers as Components
Microprocessor varieties z. Microcontroller: includes I/O devices, onboard memory. z. Digital signal processor (DSP): microprocessor optimized for digital signal processing. z. Typical embedded word sizes: 8 -bit, 16 bit, 32 -bit. © 2000 Morgan Kaufman Overheads for Computers as Components
Application examples z. Simple control: front panel of microwave oven, etc. z. Canon EOS 3 has three microprocessors. y 32 -bit RISC CPU runs autofocus and eye control systems. z. Analog TV: channel selection, etc. z. Digital TV: programmable CPUs + hardwired logic. © 2000 Morgan Kaufman Overheads for Computers as Components
Automotive embedded systems z. Today’s high-end automobile may have 100 microprocessors: y 4 -bit microcontroller checks seat belt; ymicrocontrollers run dashboard devices; y 16/32 -bit microprocessor controls engine. © 2000 Morgan Kaufman Overheads for Computers as Components
BMW 850 i brake and stability control system z. Anti-lock brake system (ABS): pumps brakes to reduce skidding. z. Automatic stability control (ASC+T): controls engine to improve stability. z. ABS and ASC+T communicate. y. ABS was introduced first---needed to interface to existing ABS module. © 2000 Morgan Kaufman Overheads for Computers as Components
BMW 850 i, cont’d. sensor brake ABS © 2000 Morgan Kaufman hydraulic pump brake sensor Overheads for Computers as Components
Characteristics of embedded systems z. Sophisticated functionality. z. Real-time operation. z. Low manufacturing cost. z. Low power. z. Designed to tight deadlines by small teams. © 2000 Morgan Kaufman Overheads for Computers as Components
Functional complexity z. Often have to run sophisticated algorithms or multiple algorithms. y. Cell phone, laser printer. z. Often provide sophisticated user interfaces. © 2000 Morgan Kaufman Overheads for Computers as Components
Real-time operation z. Must finish operations by deadlines. y. Hard real time: missing deadline causes failure. y. Soft real time: missing deadline results in degraded performance. z. Many systems are multi-rate: must handle operations at widely varying rates. © 2000 Morgan Kaufman Overheads for Computers as Components
Non-functional requirements z. Many embedded systems are mass-market items that must have low manufacturing costs. y. Limited memory, microprocessor power, etc. z. Power consumption is critical in batterypowered devices. y. Excessive power consumption increases system cost even in wall-powered devices. © 2000 Morgan Kaufman Overheads for Computers as Components
Design teams z. Often designed by a small team of designers. z. Often must meet tight deadlines. y 6 month market window is common. y. Can’t miss back-to-school window for calculator. © 2000 Morgan Kaufman Overheads for Computers as Components
Why use microprocessors? z. Alternatives: field-programmable gate arrays (FPGAs), custom logic, etc. z. Microprocessors are often very efficient: can use same logic to perform many different functions. z. Microprocessors simplify the design of families of products. © 2000 Morgan Kaufman Overheads for Computers as Components
The performance paradox z. Microprocessors use much more logic to implement a function than does custom logic. z. But microprocessors are often at least as fast: yheavily pipelined; ylarge design teams; yaggressive VLSI technology. © 2000 Morgan Kaufman Overheads for Computers as Components
Power z. Custom logic is a clear winner for low power devices. z. Modern microprocessors offer features to help control power consumption. z. Software design techniques can help reduce power consumption. © 2000 Morgan Kaufman Overheads for Computers as Components
Challenges in embedded system design z. How much hardware do we need? y. How big is the CPU? Memory? z. How do we meet our deadlines? y. Faster hardware or cleverer software? z. How do we minimize power? y. Turn off unnecessary logic? Reduce memory accesses? © 2000 Morgan Kaufman Overheads for Computers as Components
Challenges, etc. z. Does it really work? y. Is the specification correct? y. Does the implementation meet the spec? y. How do we test for real-time characteristics? y. How do we test on real data? z. How do we work on the system? y. Observability, controllability? y. What is our development platform? © 2000 Morgan Kaufman Overheads for Computers as Components
Design methodologies z. A procedure for designing a system. z. Understanding your methodology helps you ensure you didn’t skip anything. z. Compilers, software engineering tools, computer-aided design (CAD) tools, etc. , can be used to: yhelp automate methodology steps; ykeep track of the methodology itself. © 2000 Morgan Kaufman Overheads for Computers as Components
Design goals z. Performance. y. Overall speed, deadlines. z. Functionality and user interface. z. Manufacturing cost. z. Power consumption. z. Other requirements (physical size, etc. ) © 2000 Morgan Kaufman Overheads for Computers as Components
Levels of abstraction requirements specification architecture component design system integration © 2000 Morgan Kaufman Overheads for Computers as Components
Top-down vs. bottom-up z. Top-down design: ystart from most abstract description; ywork to most detailed. z. Bottom-up design: ywork from small components to big system. z. Real design uses both techniques. © 2000 Morgan Kaufman Overheads for Computers as Components
Stepwise refinement z. At 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. © 2000 Morgan Kaufman Overheads for Computers as Components
Requirements z. Plain language description of what the user wants and expects to get. z. May be developed in several ways: ytalking directly to customers; ytalking to marketing representatives; yproviding prototypes to users for comment. © 2000 Morgan Kaufman Overheads for Computers as Components
Functional vs. nonfunctional requirements z. Functional requirements: youtput as a function of input. z. Non-functional requirements: ytime required to compute output; ysize, weight, etc. ; ypower consumption; yreliability; yetc. © 2000 Morgan Kaufman Overheads for Computers as Components
Our requirements form © 2000 Morgan Kaufman Overheads for Computers as Components
Example: GPS moving map requirements z. Moving map obtains position from GPS, paints map from local database. Scotch Road I-78 lat: 40 13 lon: 32 19 © 2000 Morgan Kaufman Overheads for Computers as Components
GPS moving map needs z. Functionality: For automotive use. Show major roads and landmarks. z. User interface: At least 400 x 600 pixel screen. Three buttons max. Pop-up menu. z. Performance: Map should scroll smoothly. No more than 1 sec power-up. Lock onto GPS within 15 seconds. z. Cost: $500 street price = approx. $100 © 2000 Morgan Overheads for Computers as cost of goods sold. Kaufman Components
GPS moving map needs, cont’d. z. Physical size/weight: Should fit in dashboard. z. Power consumption: Current draw comparable to CD player. © 2000 Morgan Kaufman Overheads for Computers as Components
GPS moving map requirements form © 2000 Morgan Kaufman Overheads for Computers as Components
Specification z. A more precise description of the system: yshould not imply a particular architecture; yprovides input to the architecture design process. z. May include functional and non-functional elements. z. May be executable or may be in mathematical form for proofs. © 2000 Morgan Kaufman Overheads for Computers as Components
GPS specification z. Should include: y. What is received from GPS; ymap data; yuser interface; yoperations required to satisfy user requests; ybackground operations needed to keep the system running. © 2000 Morgan Kaufman Overheads for Computers as Components
Architecture design z. What major components go satisfying the specification? z. Hardware components: y. CPUs, peripherals, etc. z. Software components: ymajor programs and their operations. z. Must take into account functional and non -functional specifications. © 2000 Morgan Kaufman Overheads for Computers as Components
GPS moving map block diagram GPS receiver search engine database © 2000 Morgan Kaufman renderer user interface Overheads for Computers as Components display
GPS moving map hardware architecture display frame buffer CPU GPS receiver memory © 2000 Morgan Kaufman panel I/O Overheads for Computers as Components
GPS moving map software architecture position © 2000 Morgan Kaufman database search renderer user interface timer Overheads for Computers as Components pixels
Designing hardware and software components z. Must spend time architecting the system before you start coding. z. Some components are ready-made, some can be modified from existing designs, others must be designed from scratch. © 2000 Morgan Kaufman Overheads for Computers as Components
System integration z. Put together the components. y. Many bugs appear only at this stage. z. Have a plan for integrating components to uncover bugs quickly, test as much functionality as early as possible. © 2000 Morgan Kaufman Overheads for Computers as Components
Summary z. Embedded computers are all around us. y. Many systems have complex embedded hardware and software. z. Embedded systems pose many design challenges: design time, deadlines, power, etc. z. Design methodologies help us manage the design process. © 2000 Morgan Kaufman Overheads for Computers as Components
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