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					Embedded Systems Design



     Introduction




                          1
                                       Outline
   • Embedded systems overview
          – What are they?
   • Design challenge – optimizing design metrics
   • Technologies
          – Processor technologies
          – IC technologies
          – Design technologies




                                                    2
Embedded System Design: Introduction
                        Embedded systems overview
   • Computing systems are everywhere
   • Most of us think of “desktop” computers
          –   PC’s
          –   Laptops
          –   Mainframes
          –   Servers
   • But there’s another type of computing system
          – Far more common ...the embedded systems




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Embedded System Design: Introduction
                        Embedded systems overview

    • Embedded computing systems                         Computers are in

           – Computing systems embedded within
                                                                  here...
                                                               and here...
             electronic devices
           – Hard to define. Nearly any computing         and even here...

             system other than a desktop computer
           – Billions of units produced yearly, versus
             millions of desktop units
           – Perhaps 50% per household and per
             automobile
                                                               Lots more of these, though
    • “information processing systems                           they cost a lot less each.


      that are embedded into a larger
      product.”(not directly visible to user)
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Embedded System Design: Introduction
                A “short list” of embedded systems
   Anti-lock brakes                    Modems
   Auto-focus cameras                  MPEG decoders
   Automatic teller machines           Network cards
   Automatic toll systems              Network switches/routers
   Automatic transmission              On-board navigation
   Avionic systems                     Pagers
   Battery chargers                    Photocopiers
   Camcorders                          Point-of-sale systems
   Cell phones                         Portable video games
   Cell-phone base stations            Printers
   Cordless phones                     Satellite phones
   Cruise control                      Scanners
   Curbside check-in systems           Smart ovens/dishwashers
   Digital cameras                     Speech recognizers
   Disk drives                         Stereo systems
   Electronic card readers             Teleconferencing systems
   Electronic instruments              Televisions
   Electronic toys/games               Temperature controllers
   Factory control                     Theft tracking systems
   Fax machines                        TV set-top boxes
   Fingerprint identifiers             VCR’s, DVD players
   Home security systems               Video game consoles
   Life-support systems                Video phones
   Medical testing systems             Washers and dryers

   And, the list goes on and on
                                                                  5
Embedded System Design: Introduction
    Characteristics of Embedded Systems (1)

   • Must be dependable, i.e., safety-critical (airplane,
     nuclear power, ...)
          – Reliability R(t) = probability of system working correctly
            provided that is was working at t=0
          – Maintainability M(d) = probability of system working
            correctly d time units after error occurred.
          – Availability: probability of system working at time t
          – Safety: failing system causes no harm
          – Security: confidential and authentic communication
          – Even perfectly designed systems can fail if the assumptions
            about the workload and possible errors turn out to be wrong.
          – Making the system dependable must not be an after-thought,
            it must be considered from the very beginning.
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Embedded System Design: Introduction
    Characteristics of Embedded Systems (2)
   • Must be efficient
          –   Energy efficient (low power, slow improvement of battery technology).
          –   Code-size efficient (especially for systems-on-chip)
          –   Run-time efficient
          –   Weight efficient
          –   Cost efficient
   • Dedicated towards a certain application
          – no addition program can be run,
          – No unused resource present,
          – Knowledge about behavior at design time can be used to minimize resources and
            to maximize robustness
   • Dedicated user interface
          – no mouse, no keyboard, no screen  disappearing computer.
          – simple or no user interface (push buttons, steering wheel,...)

                                                                                            7
Embedded System Design: Introduction
    Characteristics of Embedded Systems (3)
   • Many ES must meet real-time constraints
          – A real-time system must react to stimuli from the controlled
            object (or the operator) within the time interval dictated by
            the environment.
          – For real-time systems, right answers arriving too late are
            wrong.
          – “A real-time constraint is called hard, if not meeting that
            constraint could result in a catastrophe” [Kopetz, 1997].
          – All other time-constraints are called soft.
          – A guaranteed system response has to be explained without
            statistical arguments

                                                                            8
Embedded System Design: Introduction
    Characteristics of Embedded Systems (4)
   • Frequently connected to physical environment through
     sensors and actuators,
   • Hybrid systems (analog + digital parts).
   • Typically, ES are reactive systems:
     “A reactive system is one which is in continual interaction
     with its environment and executes at a pace determined by
     that environment” [Bergé, 1995]
     Behavior depends on input and current state.
      automata model appropriate,
       model of computable functions inappropriate.


                                                                   9
Embedded System Design: Introduction
      Application areas of Embedded Systems
                     •    Automotive electronics
                     •    Aircraft electronics
                     •    Trains
                     •    Telecommunication
                     •    Medical systems
                     •    Military applications
                     •    Authentication systems
                     •    Consumer electronics
                     •    Fabrication equipment
                     •    Smart building
                     •    Robotics
                     •    ....

                                                   10
Embedded System Design: Introduction
       An embedded system example -- a digital
                     camera
                       Digital camera chip
              CCD

                                             CCD preprocessor                     Pixel coprocessor                  D2A
                         A2D


           lens


                           JPEG codec                           Microcontroller                   Multiplier/Accum



                            DMA controller                                                            Display ctrl




                           Memory controller              ISA bus interface               UART               LCD ctrl




   •    Single-functioned -- always a digital camera
   •    Tightly-constrained -- Low cost, low power, small, fast
   •    Reactive and real-time -- only to a small extent

                                                                                                                           11
Embedded System Design: Introduction
  Design challenge – optimizing design metrics
   • Obvious design goal:
          – Construct an implementation with desired functionality
   • Key design challenge:
          – Simultaneously optimize numerous design metrics
   • Design metric
          – A measurable feature of a system’s implementation
          – Optimizing design metrics is a key challenge




                                                                     12
Embedded System Design: Introduction
  Design challenge – optimizing design metrics
   • Common metrics
          – Unit cost: the monetary cost of manufacturing each copy
            of the system, excluding NRE (Non-Recurring
            Engineering) cost
          – NRE cost: the one-time monetary cost of designing the
            system
          – Size: the physical space required by the system
          – Performance: the execution time or throughput of the
            system
          – Power: the amount of power consumed by the system
          – Flexibility: the ability to change the functionality of the
            system without incurring heavy NRE cost
                                                                          13
Embedded System Design: Introduction
  Design challenge – optimizing design metrics
   • Common metrics (continued)
          – Time-to-prototype: the time needed to build a working version of the
              system
          – Time-to-market: the time required to develop a system to the point that it
              can be released and sold to customers
          – Maintainability: the ability to modify the system after its initial release
          – Correctness, safety, and many more




                                                                                          14
Embedded System Design: Introduction
        Design metric competition -- improving one
                    may worsen others
                                                                                    • Expertise with both software
                                     Power
                                                                                      and hardware is needed to
                                                                                      optimize design metrics
          Performance                                                 Size
                                                                                       – Not just a hardware or
                                                                                         software expert, as is common
                                                                                       – A designer must be
                                        NRE cost
                                                                                         comfortable with various
                                                                                         technologies in order to choose
          Digital camera chip
   CCD                                                                                   the best for a given application
                        CCD preprocessor         Pixel coprocessor           D2A
          A2D
 lens
                                                                                         and constraints
           JPEG codec               Microcontroller          Multiplier/Accum

            DMA controller                                           Display ctrl        Hardware

           Memory controller      ISA bus interface     UART            LCD ctrl
                                                                                          Software



                                                                                                                            15
Embedded System Design: Introduction
           Time-to-market: a demanding design metric
                                                   • Time required to develop a
                                                     product to the point it can be
                                                     sold to customers
                                                   • Market window
  Revenues ($)




                                                      – Period during which the product
                                                        would have highest sales
                                                   • Average time-to-market
                                                     constraint is about 8 months
                                   Time (months)   • Delays can be costly




                                                                                          16
Embedded System Design: Introduction
                        Losses due to delayed market entry

                                                               • Simplified revenue model
                                          Peak revenue            – Product life = 2W, peak at W
                                           Peak revenue from      – Time of market entry defines a
Revenues ($)




                                             delayed entry
                                On-time
                                                                    triangle, representing market
               Market rise                      Market fall
                                                                    penetration
                                                                  – Triangle area equals revenue
                                Delayed
                                                               • Loss
                       D
                                                                  – The difference between the on-
                                  W                      2W
                                                 Time               time and delayed triangle areas
    On-time           Delayed
     entry             entry




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Embedded System Design: Introduction
        Design productivity exponential increase
                                                                                                              100,000


                                                                                                              10,000




                                                                                                                        (K) Trans./Staff – Mo.
                                                                                                              1,000




                                                                                                                             Productivity
                                                                                                              100


                                                                                                              10


                                                                                                              1


                                                                                                              0.1

                                                                                                              0.01




                                                                                         2005
                                               1993




                                                                           2001


                                                                                  2003
            1983




                          1987
                   1985




                                        1991
                                 1989




                                                                    1999
                                                             1997
                                                      1995




                                                                                                2007


                                                                                                       2009
   • Exponential increase over the past few decades

                                                                                                                                                 36
Embedded System Design: Introduction
                                   The co-design ladder

 • In the past:                                              Sequential program code (e.g., C, VHDL)

        – Hardware and software                         Compilers
                                                                                            Behavioral synthesis
                                                                                                 (1990's)
                                                      (1960's,1970's)
          design technologies were
                                                                                              Register transfers
          very different                             Assembly instructions                      RT synthesis
        – Recent maturation of                        Assemblers, linkers
                                                                                              (1980's, 1990's)

          synthesis enables a unified                  (1950's, 1960's)                 Logic equations / FSM's
                                                                                               Logic synthesis
          view of hardware and                                                                 (1970's, 1980's)
                                                      Machine instructions
          software                                                                               Logic gates

 • Hardware/software
   “codesign”
                                                                           Implementation
                                                  Microprocessor plus                     VLSI, ASIC, or PLD
                                                program bits: “software”              implementation: “hardware”


 “The choice of hardware versus software for a particular function is simply a tradeoff among various
    design metrics, like performance, power, size, NRE cost, and especially flexibility; there is no
            fundamental difference between what hardware or software can implement.”

                                                                                                                   37
Embedded System Design: Introduction
                  Independence of processor and IC
                           technologies
   • Basic tradeoff
          – General vs. custom
          – With respect to processor technology or IC technology
          – The two technologies are independent

                                       General-        Appl.        Single-
                                        purpose       Specific      purpose
                General,               processor     Instr.-set    processor        Customized,
          providing improved:                        Processor                  providing improved:

     Flexibility                                                                       Power efficiency
     Maintainability                                                                       Performance
     NRE cost                                                                                       Size
     Time- to-prototype                                                              Cost (high volume)
     Time-to-market
     Cost (low volume)

                                       PLD         Semi-custom    Full-custom


                                                                                                           38
Embedded System Design: Introduction
                                Design productivity gap
   • While designer productivity has grown at an impressive rate
     over the past decades, the rate of improvement has not kept
     pace with chip capacity

                       10,000                                             100,000
                        1,000                                             10,000

   Logic transistors     100                                              1000
       per chip           10                                        Gap   100          Productivity
                                       IC capacity                                 (K) Trans./Staff-Mo.
     (in millions)         1                                              10
                          0.1                                             1
                                                     productivity
                         0.01                                             0.1
                        0.001                                             0.01




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Embedded System Design: Introduction
                                Design productivity gap
   • 1981 leading edge chip required 100 designer months
          – 10,000 transistors / 100 transistors/month
   • 2002 leading edge chip requires 30,000 designer months
          – 150,000,000 / 5000 transistors/month
   • Designer cost increase from $1M to $300M
                       10,000                                             100,000
                        1,000                                             10,000
   Logic transistors     100                                              1000
                          10                                        Gap   100          Productivity
       per chip                        IC capacity
     (in millions)          1                                             10       (K) Trans./Staff-Mo.
                          0.1                                             1
                                                     productivity
                         0.01                                             0.1
                        0.001                                             0.01




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Embedded System Design: Introduction
                              The mythical man-month

• The situation is even worse than the productivity gap indicates
•       In theory, adding designers to team reduces project completion time
•       In reality, productivity per designer decreases due to complexities of team management
        and communication
•       In the software community, known as “the mythical man-month” (Brooks 1975)
•       At some point, can actually lengthen project completion time! (“Too many cooks”)
                                                                                             Team
                                       60000                               15
    •    1M transistors, 1                                          16            16
                                       50000                 19                        18
         designer=5000 trans/month
                                       40000                                                  23
    •    Each additional designer                       24
         reduces for 100 trans/month   30000
                                                        Months until completion
                                       20000       43
    •    So 2 designers produce 4900                                            Individual
                                       10000
         trans/month each
                                               0        10         20            30                40
                                                              Number of designers


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Embedded System Design: Introduction
                                   Some open 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?
 •    Which programming language provides real-time features ?
 •    How do we validate embedded real-time software?
       (large volumes of data, testing may be safety-critical)




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Embedded System Design: Introduction
                                       Summary
   • Embedded systems are everywhere
   • Key challenge: optimization of design metrics
          – Design metrics compete with one another
   • A unified view of hardware and software is necessary to
     improve productivity
   • Three key technologies
          – Processor: general-purpose, application-specific, single-purpose
          – IC: Full-custom, semi-custom, PLD
          – Design: Compilation/synthesis, libraries/IP, test/verification




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Embedded System Design: Introduction

				
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