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 1
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 2
Embedding a computer CPU embedded computer © 2000 Morgan Kaufman output analog input analog mem Overheads for Computers as Components 3
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 4
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 5
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 6
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 7
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 8
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 9
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 10
BMW 850 i, cont’d. sensor brake ABS © 2000 Morgan Kaufman hydraulic pump brake sensor Overheads for Computers as Components 11
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 12
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 13
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 14
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 15
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 16
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 17
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 18
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 19
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 20
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 21
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