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Dec 2002
A Tutorial on Embedded Systems
Arpan Pal Prateep Misra
Center of Excellence for Embedded Systems,Tata Consultancy Services, Kolkataemail : [email protected]
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• Session -1 Introduction to Embedded Systems
• Session -2 Basic Concepts of Real-Time Systems
• Session -3 Embedded System Design• Session -4 Case Study on Wireless LAN• Session -5 Emerging Areas and Trends
CONTENTS
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Session 1: Introduction to Embedded Systems
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Embedded Systems• Embedded System
– a special purpose computer which exists within a larger system / device– consists of hardware ( microprocessors, DSP, dedicated hardware ) , OS and
application software– dedicated function– are widespread
• Telecom - switches, gateways, routers• Internet appliances• Wireless & mobile devices - Phones, PDA• Automobiles - engine control, power train, safety and navigation systems• Consumer & home Appliances • Industrial automation • Medical systems
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Features• Embedded Systems
– usually have disk less operation, ROM boot– “headless” - no display , keyboard, mouse– are usually networked– require real time performance– should have high availability and reliability– usually developed around a Real Time Operating System ( RTOS)
• Embedded System Software– in form of ‘firmware’ ( i.e in a ROM )– in flash (‘disk on chips’ ) – downloadable via network
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Real time systems• Real Time System
– responds to external stimuli– responses have time deadlines – consists of hardware, application software and RTOS– all components should be such that the system meets the requirements
• Real Time Operating System– building block of an Real Time System– bounded , predictable response times under all loads– enable preemptive priority driven task scheduling so that task
deadlines can be met
Embedded Systems are often real time systems built around a Real Time OS
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An Embedded System - IP Phone
10/100 PHY
RISCFlash
RISCDRAM
DSPSRAM
DSP
RISC
DSLModem
CableModem
LANNIC
IP PhoneCODEC
IP PHONE/INTEGRATED ACCESS DEVICE
10/100 PHY
To PC
Handset
Speaker
AnalogPhones/Fax
Display
LEGENDIP Phone
IADTo LAN-
ConnectedPhones
CODEC/SLIC
CODEC/SLIC
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Technology Classifications• Core Technologies
– the technology domain of the embedded product– e.g. communication technology ( wired / wireless), imaging, automation and control– results of engineering research and development– sufficiently matured for use in real life application – expertise in core technologies is required for IP development
• Enabling Technologies– enables cost effective deployment of core technologies– e.g. embedded software, VLSI design, board design– multiple enabling technologies are required in any embedded product– expertise / skills in enabling technologies required for service engagement
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Core TechnologiesCore Technology Industry Verticals ServedCommunication Systems Telecom / Datacom , Industrial Automation, Military,
Aerospace, Remote Control / Automation, Test andMeasurement, Office Automation, Consumer Electronics
Data Communication andNetworking
Telecom / Datacom, Consumer Electronics, IndustrialAutomation, Information Automation, Retail Automation,Automotive, Test and Measurement, Office Automation
Video and ImagingTechnologies
Consumer Electronics, Medical Electronics, Military/Aerospace, Office Automation
Speech and Audio Consumer Electronics, Telecom / DatacomControl Systems Industrial Automation, Military / Aerospace, Automotive,
Information Automation, Remote Control
Note
• The above list is representative only
• Each core technology may find applications in other verticals as well
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Enabling Technology Components
ASIC/ FPGA
Tools RTOS Internals
RTOS Middleware
Embedded Application
Board Level Design
DSP Cores
DSP Algorithms
Hardware
Firmware & BSP
Middleware and
Applications
GPP Cores
Analog/RF & Mixed Signal
Enabling technologies can be divided under the following three areas
• Hardware Design - Fabless Semiconductor and Board Design
• Firmware and Board Support Packages
• Middleware and Applications
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Industry VerticalsTelecom / Datacom
• Infrastructure equipment such as switches and routers (both wired and wireless)• Enterprise network equipment such as remote access concentrators• Client equipment like network cards (both wired and wireless) • Consumer devices such as mobile phones and internet phones.
Industrial Automation
• Digital motor control• Process Control and Measurement Systems• Industrial equipment controllers• Robotics• Bar code scanner, • Power line monitoring, UPS
Military / Aerospace
• Radar Systems• IR image processing• Missile guidance and navigation • Satellite image processing• Voice encryption• Fire control
Consumer Electronics
• Set-top boxes• DAB, HDTV• Digital camera• Digital answering machine, cordless phone• Video games , MP3 players• Internet Appliances
• Home Networking Gateways.
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Industry Verticals ( contd. )Test and Measurement
• Test and measurement instruments• Signal Generators• Signal Analysers• Oscilloscopes and Logic Analysers• Test and Debug tools
Automotive
• Hard Real Time controllers in engine, brakes and chassis systems• Automotive console - soft real-time, graphics intensive in-car computing/navigational and control information and entertainment terminals
Medical Electronics
• Patient monitoring systems• Imaging equipment • Pathological lab instruments
Office Automation
• Smart copiers• Fax machines• Printers• Scanners
• Multifunction Peripherals .
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Industry Verticals ( contd. )Retail Automation
• Point of Sale systems• Info kiosks• Automatic identification systems• Smart Shelves
Information Automation
• RAID devices• Disk/tape drives• Disk Servo Controller• Server Appliances
Remote Control / Automation
• Building automation• Automated Utility meters• Security Systems
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Engineering challengesTechnical Challenges• Installing new versions is complicated
– fixing bugs may mean product recall– downtime may not be tolerated . For example bug fixing in a running telecom
switch may mean huge monetary loss if network is brought down
• Extreme cost of failure– failure of medical systems could lead to death
• Restricted operational environment – attempts to lower cost may mean that only low power CPUs and less memory
available for applications.
• Real time response– system must provide guaranteed response times
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Cost challenges• Need to provide customer with greatest possible value, satisfaction at
given price
• Product value and competitive needs to be assessed with respect to cost of the product
• Bill of Materials must be carefully selected to provide best possible product features at least cost to consumer
• Engineering design and development cost need to be carefully controlled throughout the life cycle
• Product must have distinguishing and differentiated features when compared with competing products - yet costs must be kept low
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Other challengesTime to Market Challenges• If product is late , business opportunity • Most embedded systems development projects have schedules less than one year• Project schedules and features to be developed have to be carefully balanced Technology Choice ChallengesThe choice of software and hardware technology by OEMs is always associated
with the following questions:• Will the technology be available for the life of the product?• Is the technology robust enough to meet evolving industry,market,and
application needs?• Can the technology be extended so that it scales for future products?• Are there enough adopters,partners,and special interest groups (SIGs)so that
the technology will have a longer life and remain superior to competitive choices?
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Session 2: Basic Concepts of Real-Time Systems
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Terms and Concepts
• A real-time system is a system with performance deadlines on computations and actions; i.e; system correctness depends on the timeliness of results
• An embedded system is a system that exists within a larger system
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Definitions - Real-Time Systems
– A real-time system is a system that must satisfy explicit (bounded) response-time constraints or risk severe consequences, including failure
– A real-time system is one whose logical correctness is based on both the correctness of the outputs and their timeliness.
– A real-time system responds in a (timely) predictable way to unpredictable external stimuli arrivals.
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Definition - Response Time
– The time between the presentation of a set of inputs to a system and the appearance of all the associated outputs is called the response time of the system
time
Event Arrival
Response Time
Event Arrival Deadline
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Real-Time System Categories
• Hard real-time– Missing a deadline bears catastrophic results
• Firm real-time– Missing a deadline has a non-acceptable quality reduction as
a consequence
• Soft real-time– Missing a deadline is undesirable, but not fatal
• Non real-time– No Deadlines
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Hard Vs Soft Constraints
– Value of Result
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– A real-time system is a soft real-time system when actions have soft deadlines
Soft Real-Time Systems
Non-Stringent Timing Requirements– on-line transaction system– telephone switches
More Stringent Timing Requirements– Stock Price quotation system
Stringent Timing Requirements– Multimedia
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Timing Constraints
• A timing constraint is the constraint imposed on the timing behavior of an action
– Periodic - tasks arrive at fixed intervals,
called periods
– Aperiodic (Sporadic) - tasks may arrive any
time after a minimum interval
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Task Model
• Event-Driven (Reactive) Tasks primarily
react to external events which are generally
aperiodic (sporadic).
• Time-Driven Tasks are driven by the
passage of time or time epochs; generally
periodic tasks.
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Event Driven Task
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Time Driven Task
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Real-time Systems Characteristics
• Timeliness– Meeting Deadlines– Hard and soft RT systems– Performance budgets
• Responsiveness– Reactive– Irrespective of time or order of event
arrival, the system should respond
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Real-time Systems Characteristics• Concurrency
– Ability to handle multiple events– Multi tasking
• Predictability– Extent to which the characteristics is known
in advance– Static scheduling vs Dynamic scheduling
– Using Cyclic executives, avoid preemption, No virtual memory
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Real-time Systems Characteristics...
• Correctness and Robustness– Doing right things all the time– Doing right under unplanned circumstances– Identify fault and take evasive action
(deadlocks, race conditions, starvation etc)
• Dealing with Resource Limitation
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Scheduling Algorithms• Static
– Static scheduling operates on the set of tasks and constraints to generate a fixed schedule
– Static scheduling can be used if the scheduling algorithm has complete knowledge of the task set and all constraints such deadlines, execution times, precedence, and future arrival times
• Dynamic– Dynamic scheduling is performed at run-time– Dynamic scheduling algorithms have complete knowledge of
currently active tasks, but new tasks may arrive at any time in the future
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Scheduling Evaluation Metrics
• processor utilization
• sum of task completion times
• weighted sum of task completion times
• schedule length
• number of processors required
• maximum lateness
• missed deadlines
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Concurrency
• Simultaneous execution of multiple sequential chains of actions
– Pseudo-Concurrency - chains of actions execute on one processor (Multitasking)
– True-Concurrency - chains of actions execute on multiple processors (Multiprocessing)
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Types of Concurrency
• Concurrent activities may be– Non-interacting– Interacting– e.g. Traffic on parallel and intersecting roads
• Interacting activities– share common resources– needs co-ordination
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Realizing Concurrency
• Multiprocessing– Multiple CPUs– Each CPU executing one thread of control
• Multitasking– Multiple tasks– Processes or threads
• Context switching, Heavy or light
– States• Running, Ready, Blocked
• Application based solutions– Branching within code
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Designing for Concurrency
• Task Management– how to come up with tasks?
• Inter-Task Communication– how to decide on what to use ?
• Synchronization & Mutual Exclusion– how to create concurrency
• External Event Handling
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Task Management
• Task – single threaded sequential set of instructions
with its own stack space
• starting point for initializing data
• private memory space for maintaining execution context - on an independent stack, maintained by the OS
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Task Management - Creation• Task Creation
– Static Task Creation
• stack space, priority , etc allocated before run time
– Dynamic Task Creation
• Tasks created at run time
– Static Creation is preferred as
• Know resource demands in advance
• no performance degradation, can be measured
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Inter Task Communication• ITC Mechanisms
– Shared Memory• Simple sharing of data
– Semaphores• Basic Synchronization and Mutual Exclusion
– Message Queues/Pipes• Intertask message passing within a CPU
– Sockets and Remote Procedure Calls• Network transparent Intertask communication
– Signals• Exception Handling
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Synchronization & Mutual Exclusion
• Synchronization– bringing in serial behavior into concurrent tasks
– blocking one task till a resource become available
• Mutual Exclusion– avoids common data corruption between
producers and consumers of shared data
• Both combine to ensure effective and efficient sharing of common resources
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Synchronization & Mutual Exclusion
Counter Thread
GUI Thread
Data
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Synchronization & Mutual Exclusion ...• Pitfalls
– Deadlock
– Starvation
– Lockout
– Priority inversion
– Race conditions
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Session 3: Embedded System Design
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Embedded System Design Components
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Embedded System Design Chain
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Fabless Hardware DesignVLSI Design• custom design and implementation of functionality in silicon• requires technology independent designs ( ‘Front End’) and
technology dependant ‘Back End’ designs and optimizations• done by using sophisticated EDA tools for simulations, synthesis,
floor-planning, layout, static analysis etc.• chips so designed form essential components of embedded systems• VLSI design required for following domains - Analog and Mixed
signal, Custom ASIC, FPGA designs, processors cores - DSP and GPP
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Design Entry
Logic Synthesis
System Partitioning
Floor planning
Tapeout
Place & RouteCircuit Extraction
Simulations
Simulations
Work Products Tools Skills
HDL code
Netlists Synopsis DesignCompiler
Simulators - NC-Verilog,Schematic entrytools
Verilog/VHDL,Verilog/Analog
Logic Synthesis,Timing AnalysisOptimization
Delays, TimingInfo, Parasitics,GDS -II tapeout
Cadence backend tools
Physical design skills
ASIC design workflow
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Board Level Design• Board design is a specialized activity in embedded system
development. • Most of the embedded system applications require small size, low-
form-factor PCBs• Design should care of high-speed, noise and heat dissipation• Board design complexities are due to
– Higher speed processors - 200 to 600 MHz– More peripherals , including analog circuits on smaller form factors– Low power issues
• Proper usage of these tools can reduce the Board-Level-Design iterations to a minimal level.
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Software
SOC(ASIC / ASSP)
ProgrammableDSP
Microcontroller
FPGA / EPLD
ReconfigurableArchitecture
Programmability
Pow
er & S
pace O
ptimization
Analog, Mixed Signal,
RF
Hardware Platforms
Software
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Algorithm Design and Simulation
VHDL Conversion
Functional Simulation
FPGA Synthesis
MATLAB / SPW / C
System Generator
ModelSim/ NCSim
Xilinx ISE
Testing on Board
ASIC/SOC Synthesis
Physical Design
Fabrication
Testing on Board
Synthesis Tools
Physical Design Tools
Fab
Reference Board
DesignedBoard
Design Flow for FPGA / SOC based Approach
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Algorithm Design and Simulation
C Conversion
Assembly Optimization
MATLAB / SPW / C
RealTimeWorkshop
CompilerTools
Testing on Board
ASIC/SOC Synthesiswith DSP softCore
Physical Design
Fabrication
Testing on Board
Synthesis Tools
Physical Design Tools
Fab Reference Board
DesignedBoard
Design Flow for Programmable DSP / SOC based Approach
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Algorithm Design and Simulation
C Conversion
Partitioning
MATLAB / SPW / C
RealTimeWorkshop
CompilerTools
Testing on Board
ASIC/SOC Synthesiswith Reconfigurable
softCore
Physical Design
Fabrication
Testing on Board
Synthesis Tools
Physical Design Tools
Fab
Reference Board
DesignedBaseband
Board
Reconfigurable Proc Config
Design Flow for Reconfigurable DSP / SOC based Approach
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EDA Tools for Digital Hardware Design• Algorithm Simulation Tools
• MATLAB / Scilab• Elanix• Cadence Signal Processing Workbench
• Algorithm Conversion Tools• MATLAB to C – Real-Time Workshop• MATLAB to VHDL – System Generator
• Function VHDL Modelling• ModelSim• NCSim
• HDL Implementation IDE• Xilinx ISE Tools for FPGA
• Synthesis Tools• Synopsis
• Physical Design Tools• Cadence
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Embedded Software Platforms
• Real-Time Operating Systems• Kernel
• Multi-Tasking and Scheduling• Shared-Data (Semaphores)• Inter-Process-Communication (MessageQueue, Mailbox, Pipe)• Timers and Interrupts• Memory Management• Events
• Board-Support Pack• Memory Mapping and Addressing• Basic System Drivers• Peripheral Drivers
• Desirable features • scalability, robustness, real-time response, memory footprint etc.
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Middleware and Application• Embedded Middleware (Protocol Stacks and Software Frameworks)
– set of code that sits on top of RTOS BSP– implements a piece of functionality and provides service to the applications around that functionality– example - TCP/IP stacks , software development frameworks like Multimedia Home Platform (MHP)
• DSP Algorithms– core signal processing algorithms – implemented on specialized hardware like DSP Processor, FPGA and ASICs – examples - speech codecs, echo canceller, communication physical layer etc
• Embedded Application– actual application that runs on top of the middleware – provides the end-user with a set of well-defined services– Example - user interfaces
– complexity and size depends upon the domain it is catering to and the desired application features
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Embedded Software Design & Development Tools
• Host Tools• Compilers• Linkers• Debuggers• Simulators• Emulators• PROM / Flash Programmers
• Target Tools• Monitors• Target Agents• Real-Time Debuggers
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Embedded Software Design Flow• System Requirement Specification• System Interface Specification• High and Low Level Design Document• Test Specification Document• Code Development• Compile and Link• Test / Debug on Simulator / In-circuit Emulator / ROM Emulator• Port to Actual System• Embed Compiled and Linked Code to ROM / Flash• Load and Execute Code on Target using Bootloader• Test / Debug on Target• Interface with other sub-systems• Final Integration and Testing
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Development process
Analysis & Design
Write Code
Compile code
Download RTOS kernel
Download Application code
Test & Debug
Boot target
Load RTOS kernel
Load Application modules
Test & Debug
Ethernet LinkBoot Code in ROM
Ethernet Link
Ethernet Link
Loader
Login, debugger
Kernel
Symbol table
Shell
OOAD, UML
C, C++, Java, Assembly
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Embedded Software Design Issues
• Real-Time Interrupt Response• Real-Time Context Switching based on Priority • Code-Memory Optimization (Flash / ROM size)• Data-memory Optimization (RAM size)• Speed Optimization• Power Management• Power Optimization
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Hardware-Software Standard Design Flow
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Hardware-Software Co-Design Flow
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Session 4: Case Study of Wireless LAN
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802.11 WLANA 802.11 system has the following components
• RF and Analog front-end – 5 GHz for 802.11a and 2.4 GHz for 802.11g
• Baseband– PHY: 802.11a available standard, 802.11g the future.– MAC: mainly follows the original 802.11 standard, possible
ratification coming from 802.11e, 802.11f and 802.11i. Can be implemented partly on Baseband Processor and partly on Host Driver
• Hardware System– Baseband Board (including host interface) and RF board
PCI Interface
Baseband Processor
DAC
ADC
RF and Analog
FrontEnd
HostNetwork
Stack
Hos
tD
rive
r
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802.11 RF Sub-System
Base Band System(With ADC And DAC)
Baseband And Loop Filter
Radio on ChipTransreceiver
RFSwitch
RFFilter
Crystal Oscillator(Reference Frequency of PLL)
HPA/LNA
Antenna
• Designed as RFIC Chipset• RF and Analog EDA design tools used
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802.11 Baseband Processing
• 802.11 MAC• Authentication• Association • Media Access Control (CSMA/CA)• Data Framing and Fragmentation• Management services• MAC-LLC Interface• MAC-PHY Interface
• 802.11 PHY• Error Control Coding – Convolutional Code• Modulation Mapping – BPSK/QSK/QAM• DSSS (802.11b)• OFDM (802.11a)• PHY-MAC Interface• PHY-Analog & RF Interface
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802.11 Software Partitioning
Network Layer
Application Layer
LLC Sub layer
Asynchronous Data Services
Control Services
FragmentationManagement Services
MIBPower Control
Synchronization
Security Services
WEP
Authentication
Physical Layer
Physical Layer Management Entity (PLME)
MLME_PLME_SAP
MSDU Exchange
MPDU Exchange
PLCP Sub layer
PMD Sub layer
MAC Sub Layer
PHY_SAP
PMD_SAP
MAC_SAP
…Network Layer
Application Layer
LLC Sub layer
Asynchronous Data Services
Control Services
FragmentationManagement Services
MIBPower Control
Synchronization
Security Services
WEP
Authentication
Physical Layer
Physical Layer Management Entity (PLME)
MLME_PLME_SAP
MSDU Exchange
MPDU Exchange
PLCP Sub layer
PMD Sub layer
MAC Sub Layer
PHY_SAP
PMD_SAP
MAC_SAP
…Wireless Apps
Middleware TCP/IPStack
Host RTOS & BSP
Embedded CPU& ASIC/SOC
ASIC / SOC
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Session 5: Emerging Areas and Trends
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• Hardware / Software Co-Design
• Design for Test
• System Specification
• Low power design
Research Areas
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Hardware - Software Co-designObjectives - Develop methods and tools for the description, evaluation
and partitioning of application-specific computer systems which consist of both hardware and software components
Some specific topics -
• System architecture for mixed hardware/software implementations
• Unified design representation of hardware and software
• Algorithms and techniques for automatic partitioning of systems into hardware and software
• Co design of systems with real-time constraints
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Design for Testability and Self testObjectives - develop design for testability methodologies and tools to facilitate
testing of complex digital systems consisting of heterogeneous components
Some specific topics -
• System design for testability architectures • Computer-aided test - to develop design aid tools to help designers to perform
testability analysis, test strategy selection, test-driven partitioning, and test structure implementation
• Synthesis for testability • develop efficient self-test methodologies and tools for the design of competitive
embedded systems
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System Specifications
• Implementation independent specification of embedded systems
• Synthesis of high level specifications into synthesizable and compilable code ( E.g. Matlab to VHDL )
Speed Optimisation• Intelligent architecture aware compilers
• Software thread integration for hardware to software migration
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Low Power Design
• Design of tools and techniques for minimization of power consumption in embedded applications
• Low power re-configurable hardware for wireless systems
• Low power sensor networks
• Energy efficient wireless communication under QoS constraints
• Power profilers and optimizers for software
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Thank You.
