29-05-2010, 08:48 PM
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Embedded Systems
Theory and Design
Anupam Basu
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Course overview
Tentative contents:
¢ Introduction to Embedded Computing
¢ Embedded System Hardware
¢ Embedded Computing Platform
¢ Programming Embedded Systems
¢ Embedded System Development
6. Case Study and Assignments for Designing a Complete System
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Course Overview
¢ Evaluation criteria:
Term papers / Seminars/ Projects : 40% (20% will be clubbed with end term marks and 20% will contribute as Teacher's Assessment)
Mid Term (written): 20%
End Term (written): 40%
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What is an Embedded System
An Embedded System is a microprocessor based system that is embedded as a subsystem, in a larger system (which may or may not be a computer system).
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Application areas
¢ Automotive electronics
¢ Aircraft electronics
¢ Trains
¢ Telecommunication
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Application areas
¢ Authentication
¢ Military applications
¢ Medical systems
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Application areas
¢ Consumer electronics
¢ Smart buildings
¢ Fabrication equipment
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Essential Components
¢ Microprocessor / DSP
¢ Sensors
¢ Converters (A-D and D-A)
¢ Actuators
¢ Memory (On-chip and Off chip)
¢ Communication path with the interacting environment
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Embedded System Structure
(Generic)
Memory
Processor & ASICs
A-D
Sensor
D-A
Actuator
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Essential Considerations
¢ Response Time -- Real Time Systems
¢ Area
¢ Cost
¢ Portability
¢ Low Power (Battery Life)
¢ Fault Tolerance
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Design Issues
(Hardware-Software Co-design)
¢ System Specification
o Functions, Real Time Constraints, Cost and Power Constraints
¢ Hardware Software Partitioning
¢ Hardware Synthesis
¢ Software Synthesis and Code Generation
¢ Simulation
¢ Implementation
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ES, MS and RTS
¢ All embedded systems are microprocessor based systems, but all microprocessor basedsystems may not be amenable to embedding (Area, Power, Cost, Payload parameters).
¢ Most of the embedded systems have real time constraints, but there may be ES which are not hard RTS (for example off line Palm tops)
¢ There may be RTS which are not embedded (e.g. Separate Process Control Computers in a network)
¢ Embedded Systems are not GPS; they are designed for dedicated applications with specific interfaces with the sphere of control
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General Characteristics of Embedded Systems
¢ Perform a single task
o Usually not general purpose
¢ Increasingly high performance and real time constrained
¢ Power, cost and reliability are important considerations
¢ HW-SW systems
o Software is used for more features and flexibility
o Hardware (processors, ASICs, memory etc. are used for performance and security
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General Characteristics of Embedded Systems (contd.)
ASIC s
Processor Cores
ASIPs and ASICs form a significant component
o Adv: customization lower power, cost and enhanced performance
o Disadv: higher development effort (debuggers, compilers etc.) and larger time to market
Mem
Analog IO
Digital
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Classification of Embedded Systems
¢ Distributed and Non distributed
¢ Reactive and Transformational
¢ Control dominated and Data dominated
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Application Specific Characteristics
¢ Application is known before the system is designed
¢ System is however made programmable for
o Feature upgrades
o Product differentiation
¢ Often application development occurs in parallel to system development
o Hw-Sw partitioning should be as delayed as possible
¢ For upgrades design reuse is an important criterion
o IP reuse, object oriented development
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DSP Characteristics
¢ Signals are increasingly being represented digitally as a sequence of samples
¢ ADCs are moving closer to signals; RFs are also treated digitally
¢ Typical DSP processing includes:
o Filtering, DFT, DCT etc.
o Speech and image: Compression, decompression, encryption, decryption etc.
o Modems: Equalization, noise and echo cancellation, better SNR
o Communication channel: encoding, decoding, equalization etc.
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Distributed Characteristics
¢ Components may be physically distributed
¢ Communicating processes on multiple processors
¢ Dedicated hw connected through communicating channels
¢ Often economical
o 4 x 8 Bit controllers may be cheaper than a 32 bit microcontroller
o Multiple processors can perform multiple time critical tasks
o Better logistics “ devices being controlled may be physically distributed
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Design Metrics
¢ Unit cost “ the $ cost for each unit excluding development cost
¢ NRE cost: $ cost for design and development
¢ Size: The physical space reqd. “ determined by bytes of sw, number of gates and transistors in hw
¢ Performance: execution time or throughput of the system
¢ Power: lifetime of battery, cooling provisions
¢ Flexibility: ability to change functionality without heavy NRE cost
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Design Metrics (contd.)
¢ Time to market = Time to prototype + Time to refine + Time to produce in bulk
¢ Correctness: Test and Validation
¢ Safety:
¢ Often these metrics are contradictory “ hence calls for optimization
¢ Processor choice, partitioning decisions, compilation knowledge
¢ Requires expertise in hw and sw both
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Major Subtasks of Embedded System Design
¢ Modeling the system to be designed and constraints
o Experimenting with different algorithms and their preliminary evaluation
o Factoring the task into smaller subtasks and modeling their interaction
¢ Refinement
¢ HW-SW partitioning
o Allocating the tasks into hw, sw running on custom hw or general purpose hw
¢ Scheduling “ allocation of time steps for several modules sharing the same resource
¢ Implementation: Actual hw binding and sw code generation
¢ Simulation and Validation
¢ Iterate if necessary
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What is Co-design
¢ Traditional design
o SW and HW partitioning done at an early stage and development henceforth proceeds independently
¢ CAD tools are focussed towards hardware synthesis
¢ For embedded systems we need several components
o DSPs, microprocessors, network and bus interface etc.
¢ HW-SW codesign allow hw and sw design to proceed in parallel with interactions and feedback between the two processes
¢ Evaluation of trade offs and performance yields ultimate result
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CAD for Embedded Systems
¢ Co-design: Joint optimization of hw and sw to optimize design metrics
¢ Co-synthesis: Synthesizes designs from formal specifications
¢ Rapid prototyping and design space exploration
¢ Many of the tasks are interrelated
¢ Intermediate evaluation is not easy as a later decision in one path affects the other
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A Mix of Disciplines
¢ Application Domain (Signal processing, control ¦)
¢ Software Engg. ( Design Process plays an important role)
¢ Programming Language
¢ Compilers and Operating System
¢ Architecture “ Processor and IO techniques
¢ Parallel and Distributed Computing
¢ Real Time Systems
Importance of Embedded Software
and Embedded Processors
... the New York Times has
estimated that the average
American comes into contact with about 60 micro-processors every day.... [Camposano, 1996]
Latest top-level BMWs
contain over 100 micro-
processors
[Personal communication]
Most of the functionality
of embedded systems
will be implemented in software!
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¢ It is estimated that each year embedded software is written five times as much as 'regular' software
¢ The vast majority of CPU-chips produced world-wide today are used in the embedded market ... ; only a small portion of CPU's is applied in PC's
¢ ... the number of software-constructors of Embedded Systems will rise from 2 million in 1994 to 10 million in 2010;
... the number of constructors employed by software-producers 'merely' rises from 0.6 million to 1.1 million.
[Department of Trade and Industry/ IDC Benelux BV: Embedded software research in the Netherlands. Analysis and results, 1997
(according to: scintilla.utwente.nl/shintabi/engels/thema_text.html)]
Views on embedded System
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Some problems
¢ How can we capture the required behaviour of complex
systems
¢ How do we validate specifications
¢ How do we translate specifications efficiently into
implementation
¢ Do software engineers ever consider electrical power
¢ How can we check that we meet real-time constraints
¢ How do we validate embedded real-time software
(large volumes of data, testing may be safety-critical)
