1-embedded systems an introduction-r

8/7/2019 1-Embedded Systems An Introduction-R

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Embedded SystemsInstructor: Shaftab Ahmed

Lecture # 1

Reference

Embedded System DesignVahid / Givargis


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2/18/2011 Embedded Systems Spring 2011 Shaftab Ahmed 2

An embedded system is a special-purposecomputer system designed to perform one or a fewdedicated functions, often with real-time computingconstraints.

It is usually a part of complete device includinghardware and mechanical parts.On the other hand a general-purpose computer likePersonal Computer, can do many different tasks

depending on programming.Embedded systems control many of the commondevices in use today e.g. Washing Machine, Camera,Mobile and Microwave Oven etc.

What is an Embedded System


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More Examples of Embedded Systems

Air conditioner ATM machineBattery charger

Digital cameraDVD player Fax machineHome security systemMobile phone

Modem

Navigation systemPDAPhotocopier Printer Router Scanner TVVideo game consoleWearable computer


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History

In the earliest years of computers in 1930 40s,computers were sometimesdedicated to a single purposetask.

One of the first recognizablymodern embedded systemwas the Apollo GuidanceComputer

Developed by Charles StarkDraper at the MITInstrumentation Laboratory .


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Characteristics (1/4)

Special-purposeTypically designed toexecute a single programsequence repeatedly

Washing Machines

Microwave Oven


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Tightly constrainedLow costSimple systemsFewer components based

Performs functions fastenoughMinimum power


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Reactive and real-timeReactive: Continually reacts to external eventsReal-time: Must compute certain results in real-time


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Hardware and software co-exist

The software written for embedded systems isoften called firmware

Is stored in read-onlymemory or Flash memorychips rather than a diskdrive


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Differences from usual computer programs

Several components of vastlydifferent functionalities are found inembedded system softwareEach software component executionspeed must be optimumSoftware must have controlledcomplexity and must be thoroughlytested and debugged for errorsResponse time constraint and strictdeadlinesAll components must use the

memory optimally


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Real-Time Operating System

RTOS is essential for large scale embedded systems.It is an Operating System for response time-controlled and event-controlled processes.


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Real-Time Operating System

Modules of a RTOS include:1. Basic OS function2. Time Management3. Predictability4. Priorities Management5. IPC Synchronization6. Time slicing7. Hard and soft real-time operability


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Embedded OS players

Mentor Graphics VRTXPalm Computing PalmOSSymbian SymbianOSReal-time control Embedded NT/XPInternet devices Windows CE (CE.NET)Handheld PCs and PDAs Pocket PC 2002Open Software RTLinuxTiny Operating System TOS


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System on chip (SoC)

SoC Integrates all components of a computer or other electronic system into a single integrated circuit (chip).It may contain digital, analog, mixed-signal, and oftenradio-frequency functions all on one chip.Typical application of SOC is embedded systems likeMicrowave oven controller.SiP (System in Package) contains a SoC in anapplication package to perform intelligent functions


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Software Development

The software development process can berepresented by lifecycle e.g.SDLC System Development Life CycleWaterfall or Linear incremental modelFour stages of developing an embedded system

AnalysisDesign

ImplementationMaintenance


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U ser Interface

Embedded systems range fromNo user interface at allDedicated only to one taskFull user interfaces similar todesktop operating systems indevices such as PDAs.


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Digital Camera Functional Block Diagram


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Challenges and Opportunities

ChallengesDiversity of operating environments and platformsposes a real challenge in deploying software acrossmultiple platforms and configurations.Portability and reusability of the applications.

OpportunitiesOpen Software Development i.e. U se of embeddedoperating systems providing POSIX interface.


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Implementation Issues

Computing performanceIn a real time embedded control environment is not simply aninstructions- per-second rating.

While raw computational performance is important, other factors which are vital to system performance include interruptresponse characteristics, context switching over head, and I/Operformance.Since real time tasks are characterized by frequent, oftenunpredictable events, the performance of a processor athandling interrupts is crucial to its suitability for real time

processing.Since a control application usually involves a reasonableamount of communication with the outside world (such asreading sensors and activating control circuits), good I/Operformance is also important.


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Implementation Issues:

The same resource must be shared betweendifferent tasks.

Sharing As a result of this competition for the CP U use, thetiming of the tasks is not fully determined and thetime delays should be taken into account.

Alternative control algorithms should be ready to get the control of the process.

Adaptation:Working in a changeable environment, the controlgoals and options may change and the controlalgorithms should be adequate to new scenarios.


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Working conditions, such as priority, allocated timeand memory or signals availability may change.

Thus, complexity, structure and basic propertiesof the control system will change.

V ariable delays should be considered .The synchronicity of signals cannot be ensuredanymore.

V alidation and certification. Any embedded control system should be provedto be reliable and safety operation should beensured.

Implementation Issues:


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General Purpose Processors

Data Path consists of thecircuitry for transforming dataand for storing temporary data.

It contains AL U and Register File

The functionality available inGeneral Purpose Processorsinclude:

Control U nitCP U Register files

On-Chip Multi level CachesInstruction Set ArchitectureOn-Chip peripheralsPipeline RequirementsMultiplicity of CP U coresArithmetic Computation


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Single-purpose processors (SPP)

Single-purpose processors containdigital circuits designed to executeexactly one program e.g. coprocessor,accelerator or peripheralFeatures

Contains only the componentsneeded to execute a single programNo program memory

BenefitsFastLow power Small sizeSmall Datapath


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2/18/2011 Embedded Systems Spring 2011 Shaftab Ahmed23

Digital Signal Processor (DSP)

DSP is an example of single purpose processor that is highlyoptimized to process large amounts of dataIt usually contains many registers, memory blocks, multipliersand other arithmetic units

DSPs are used for filtering, transformation etc using functions likeMultiply and Accumulate etcThe source for such data may be a digital camera, voice packet or an audio clip


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Application-specific processors (ASP)

Programmable processor optimized for a particular class of applications having common characteristicsCompromise between general-purpose and single-purpose processors

FeaturesProgram memoryOptimized datapathSpecial functional units

BenefitsSome flexibilityGood performance, size and power


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Embedded Processors

An Embedded Processor is a special purpose processor whichwhen used in an embedded system design can perform onlydedicated one or few tasks.It differs from the normal general purpose computers likeservers and personal computers in the sense that later can beprogrammed to perform diverse range of tasks.Why design an embedded processor when the general purposecan serve the same purpose?

Cost reductionEnergy efficiencySize reduction (Such as SmartDust in MEMS/mote)Tailored for almost anything depending upon requirementssuch as specialized Signal Processing capability


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Embedded Processors

Some of the areas of application for Embedded Processorsinclude:

Portable Devices: PDAs, Digital Cameras, MP3 players,Mobile phones

Automotives: automobile engine control systems,Tracking systems, Functionality check systemsNetworking: Ethernet switches, routersMedical Equipment: Medical Imaging and video of insideof body, U ltrasounds etcIndustrial Controls: Nuclear Reactor Control, LatheMachine Controls etc


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Comparison of GPP and Embedded Processor

Functional Block Diagram of theembedded processor

Functional Block Diagram of theGeneral purpose CISC processor.

In addition to differences abovethe instruction set architecture is also different


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Embedded Processing Areas

The latest application and research areas for embeddedprocessor architectures include:

Wearable ComputingU biquitous ComputingSystem On ChipMultiprocessor System On ChipNetwork on Chip


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Full-custom IC

All layers are optimized for an embedded systemsparticular digital implementation like:

Placing transistorsSizing transistorsRouting wires

BenefitsExcellent performance, smallest size, low power DrawbacksHigh Non-Recurring Engineering (NRE) cost (e.g.,$300k), long time-to-market, high risk


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Gate Array

FeaturesLower layers are fully or partially builtDesigners are left with routing of wires and maybeplacing some blocks

BenefitsGood performance, good size, less NRE cost than afull-custom implementation (perhaps $10k to $100k)

Drawbacks

Still require weeks to months to develop


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Standard Cell

FeaturesInstead of designing the actual silicon, the designer uses pre-built blocks that have already been testedand proven.

BenefitsGood performance, good size, less NRE cost than afull-custom implementation (perhaps $10k to $100k)

Drawbacks

Still require weeks to months to develop


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PLD (Programmable Logic Device)

All layers already existDesigners can purchase an ICConnections on the IC are either created or destroyed to implement desired functionality


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PLD (Programmable Logic Device)

Field-Programmable Gate Array (FPGA)Benefits

Low NRE costs, almost instant IC availabilityDrawbacks

Bigger, expensive (perhaps $30 per unit), power hungry, slower


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Independence of processor & IC technologies

Basic tradeoff General vs. customProcessor technology or IC technology


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ES development methodology

Classical development was done through separatehardware and software developer teams whointegrated their work towards the end which lacked indesired optimization levels and turn around time etc.

Recent trend is to use a U nified view of the designprocess for Hardware and SoftwareHardware synthesis tools have changed the role of hardware designers essentially to write sequentialprograms through HDLHardware / Software Co-Design is a field thatemphasizes a unified view of hardware and softwarefor which synthesis tools and simulators are used


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U nified View of Design Process

Co Design Ladder


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Conclusion Revisiting


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Embedded Processor Architecture

Factors influencing embedded processor architecture:R eal-time processing:Some computation must be done within a certain time frame, or else the system would fail. Consider the following example:

A system fetching/compressing/sending voice dataTiming constraint:

It must fetch the voice data after every specified interval, it must compress/decompress/send the audio data within acertain time frame (e.g. 22.5 msec in a MELP algorithm), and then transmit it to a remote end or human ear in that

particular time, or else there may be un-acceptable voicequality degradation.


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The real-time processing can further be divided into two categories:Hard real-time system:

It is the one in which there is an absolute maximum time inwhich a certain processing has to complete.

F or example voice compression/processing must complete within

a certain dead line always.Dynamic branch predictions and cache mechanisms of thegeneral purpose processors are advantageous for the non-real- time applications, but would result in a catastrophe in the hard real-time requirements.

Soft real-time system:It is the one in which the average time of a particular task andthe number of instances may exceed by a limited time

F or example nullifying the effect of the varying inter-arrival timesof voice packets through jitter buffers over a digital voicecommunication link.


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Special signal processing capabilitiesDSPs are used for filtering, transformation etc usingfunctions like Multiply and Accumulate etcThey usually require many registers, memory

blocks, multipliers and other arithmetic units


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Power consumption:(i) These are mostly battery operated systems so long operationlife before recharging.

(ii) virtually no special cooling arrangement required decreasingcost as well as size

(iii) The application code also has to dictate the power consumption: least instruction + more work by processor =least power consumption

Limited memory:The memory size is always less in an embedded application asonly few or only one program would be required to run on it. This

factor is determined by many things.(i) size would become smaller (ii) Overall system cost would be reduced(iii) System would consume much less power

1-embedded systems an introduction-r

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