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Embedded Systems Introduction

Embedded Systems Introduction. L1. References Embedded Systems Design, Steve Heath, Elsevier Embedded Systems Design, Frank Vahid & Tony Givargis, John wiley Fundamentals of embedded software, Daniel W lewis, Pearson education

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Embedded Systems Introduction

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  1. Embedded SystemsIntroduction L1

  2. References • Embedded Systems Design, Steve Heath, Elsevier • Embedded Systems Design, Frank Vahid & Tony Givargis, John wiley • Fundamentals of embedded software, Daniel W lewis, Pearson education • Embedded Microcomputer Systems, Jonathan W Valavano, Brooks/cole, Thomson Learning • Embedded Systems Design, Oliver Bailey, Dreamtech • Embedded Real-time Systems, K V K K Prasad, Dreamtech

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

  4. Embedded systems overview • When we talk of microprocessors we think of computers as they are everywhere • Computers often mean • Desktop PC’s • Laptops • Mainframes • Servers • But there’s yet another type of computing system • Far more common...

  5. Computers/ microprocessors are in here... Embedded systems overview • Embedded computing systems • (Micro)processors are embedded within electronic devices, equipment, appliances • Hard to define - any computing system other than a desktop computer • Billions of units produced yearly, versus millions of desktop units • Perhaps 50 per household and per automobile Toys, mobile phones, kitchen appliances, even pens  Many times more processors used in each of them , though they cost much less These processors make these devices sophisticated, versatile and inexpensive

  6. A “short list” of embedded systems Modems MPEG decoders Network cards Network switches/routers On-board navigation Pagers Photocopiers Point-of-sale systems Portable video games Printers Satellite phones Scanners Smart ovens/dishwashers Speech recognizers Stereo systems Teleconferencing systems Televisions Temperature controllers Theft tracking systems TV set-top boxes VCR’s, DVD players Video game consoles Video phones Washers and dryers Anti-lock brakes Auto-focus cameras Automatic teller machines Automatic toll systems Automatic transmission Avionic systems Battery chargers Camcorders Cell phones Cell-phone base stations Cordless phones Cruise control Curbside check-in systems Digital cameras Disk drives Electronic card readers Electronic instruments Electronic toys/games Factory control Fax machines Fingerprint identifiers Home security systems Life-support systems Medical testing systems And the list goes on and on

  7. Embedded systems A microprocessor based system that is built to control a function(s) of a system and is designed not to be programmed by the user. (controller) User could select the functionality but cannot define the functionality. Embedded system is designed to perform one or limited number of functions, may be with choices or options. PCs provide easily accessible methodologies, HW & SW that are used to build Embedded systems

  8. Why did they become popular? Replacement for discrete logic-based circuits Functional upgradability ?, easy maintenance upgrades Improves the performance of mechanical systems through close control Protection of Intellectual property Replacement of Analogue circuits (DSPs)

  9. What does an Embedded system consist of? Processor – Types, technologies, functionalities Memory – how much, what types, organisation Peripherals/ I/O interfaces – communicate with the user, external environment Inputs and outputs / sensors & actuators – Digital - binary, serial/parallel, Analogue, Displays and alarms, Timing devices SW – OS, application SW, initialisation, self check Algorithms

  10. Path of electronic design Mechanical control systems- expensive & bulky Discrete electronic circuits – fast but no flexibility SW controlled circuits – microprocessors and controllers – slow, flexible HW implementation of SW, HW & SW systems

  11. Some Common Characteristics of Embedded Systems • Single-functioned • Executes a single program, repeatedly • Tightly-constrained • Low cost, low power, small, fast, etc. • Reactive and real-time • Continually reacts to changes in the system’s environment • Must compute certain results in real-time without delay

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

  13. 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

  14. Design challenge – optimizing design metrics • Common metrics • Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost • NRE cost (Non-Recurring Engineering 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: amount of power consumed by the system • Flexibility: the ability to change the functionality of the system without incurring heavy NRE cost

  15. 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, many more

  16. Expertise with both software and hardware is needed to optimize design metrics A designer must be comfortable with various technologies in order to choose the best for a given application and constraints 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 Design metric competition -- improving one may worsen others Power Performance Size NRE cost Hardware Software

  17. Time required to develop a product to the point it can be sold to customers Market window Period during which the product would have highest sales Average time-to-market constraint is about 8 months Delays can be costly Time-to-market: a demanding design metric Revenue Time (months)

  18. Simplified revenue model Product life = 2W, peak at W Time of market entry defines a triangle, representing market penetration Triangle area equals revenue Loss The difference between the on-time and delayed triangle areas Peak revenue Peak revenue from delayed entry Revenues ($) On-time Market fall Market rise Delayed D W 2W On-time Delayed entry entry Time Losses Due to Delayed Market Entry

  19. Area = 1/2 * base * height On-time = 1/2 * 2W * W Delayed = 1/2 * (W-D+W)*(W-D) Percentage revenue loss = (D(3W-D)/2W2)*100% Try some examples Peak revenue Peak revenue from delayed entry Revenues ($) On-time Market fall Market rise Delayed D W 2W On-time Delayed entry entry Time Losses due to delayed market entry (cont.) • Lifetime 2W=52 wks, delay D=4 wks • (4*(3*26 –4)/2*26^2) = 22% • Lifetime 2W=52 wks, delay D=10 wks • (10*(3*26 –10)/2*26^2) = 50% • Delays are costly!

  20. Costs: Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system total cost = NRE cost + unit cost * # of units per-product cost = total cost / # of units = (NRE cost / # of units) + unit cost Amortizing NRE cost over the units results in an additional Rs 200 per unit NRE and Unit Cost Metrics • Example • NRE= Rs 20000, unit= Rs100 • For 100 units • total cost = 20000 + 100*100 = 30000 • per-product cost = 30,000/100 or 20000/100 + 100 = 300

  21. Compare technologies by costs -- best depends on quantity ! Technology A: NRE=Rs 5,000, unit=Rs 100 Technology B: NRE=Rs 1,00,000, unit=Rs 25 Technology C: NRE=Rs10,00,000, unit= Rs 2 NRE and unit cost metrics

  22. The performance design metric • Widely-used measure of system, widely-abused • Clock freq, instructions per second – not good measures • Digital camera example – a user cares about how fast it processes images, not clock speed or instructions per second • Latency (response time) • Time between task start and end • e.g., Camera’s A and B process images in 0.25 & 0.3 seconds • Throughput • Tasks per second, e.g. Camera A processes 4 images & B say 8 images per second • Throughput can be more than latency seems to imply due to concurrency, (by capturing a new image while previous image is being stored). • Speedup of B over S = B’s performance / A’s performance • Throughput speedup = 8/4 = 2

  23. Three key embedded system technologies • Technology • A manner of accomplishing a task, especially using technical processes, methods, or knowledge • Three key technologies for embedded systems • Processor technology • IC technology • Design technology

  24. Processor technology • The architecture of the computation engine used to implement a system’s desired functionality • Processor does not have to be programmable • “Processor” not equal to general-purpose processor Controller Controller Datapath Datapath Controller Datapath Control logic index Control logic and State register Control logic and State register Registers Register file total Custom ALU State register + General ALU IR PC IR PC Data memory Data memory Program memory Program memory Data memory Assembly code for: total = 0 for i =1 to … Assembly code for: total = 0 for i =1 to … Single-purpose (“hardware”) General-purpose (“software”) Application -specific

  25. Processor technology • Processors vary in their customization for the problem at hand total = 0 for i = 1 to N loop total += M[i] end loop Desired functionality General-purpose processor Application-specific processor Single-purpose processor

  26. Controller Data path Control logic and State register Register file General ALU IR PC Program memory Data memory Assembly code for: total = 0 for i =1 to … General-purpose processors • Programmable device used in a variety of applications • Also known as “microprocessor” • Features • Program memory • General datapath with large register set and general ALU • User benefits • Low time-to-market and NRE costs • High flexibility • “Pentium” the most well-known, but there are hundreds of others

  27. Datapath Controller Control logic index total State register + Data memory Single-purpose processors • Digital circuit designed to execute exactly one program • Ex. coprocessor, accelerator Features • Contains only the components needed to execute a single program • No program memory • Benefits • Fast • Low power • Small size

  28. Controller Datapath Control logic and State register Registers Custom ALU IR PC Data memory Program memory Assembly code for: total = 0 for i =1 to … Application-specific Instruction set Processors • Programmable processor optimized for a particular class of applications having common characteristics • Compromise between general-purpose and single-purpose processors • Features • Program memory • Optimized datapath • Special functional units • Benefits • Some flexibility, good performance, size and power

  29. IC technology • The manner in which a digital (gate-level) implementation is mapped onto an IC • IC: Integrated circuit, or “chip” • IC technologies differ in their customization to a design • IC’s consist of numerous layers (perhaps 10 or more) • IC technologies differ with respect to who builds each layer & when gate oxide IC package IC drain channel source Silicon substrate

  30. IC technology • Three types of IC technologies • Full-custom/VLSI • Semi-custom ASIC (gate array and standard cell) • PLD (Programmable Logic Device)

  31. Full-custom/VLSI • All layers are optimized for an embedded system’s particular digital implementation • Placing transistors • Sizing transistors • Routing wires • Benefits • Excellent performance, small size, low power • Drawbacks • High NRE cost (e.g., Rs 2 M), long time-to-market

  32. Semi-custom • Lower layers are fully or partially built • Designers are left with routing of wires and maybe placing some blocks • Benefits • Good performance, good size, less NRE cost than a full-custom implementation (perhaps $10k to $100k) • Drawbacks • Still require weeks to months to develop

  33. PLD (Programmable Logic Device) • All layers already exist • Designers can purchase an IC • Connections on the IC are either created or destroyed to implement desired functionality • Field-Programmable Gate Array (FPGA) very popular • Benefits • Low NRE costs, almost instant IC availability • Drawbacks • Bigger, expensive (perhaps Rs 2000 per unit), power hungry, slower

  34. Moore’s law • The most important trend in embedded systems • Predicted in 1965 by Intel co-founder Gordon Moore IC transistor capacity has doubled roughly every 18 months for the past several decades 10,000 Logic transistors per chip (in millions) 1,000 100 10 1 0.1 Note: logarithmic scale 0.01 0.001 1985 1987 1989 1991 1993 1995 1997 2003 2005 2007 2009 1981 1983 1999 2001

  35. Moore’s law • This growth rate is hard to imagine, most people underestimate

  36. Graphical illustration of Moore’s law • Something that doubles frequently grows more quickly than most people realize! • A 2002 chip can hold about 15,000 1981 chips inside itself 1981 1984 1987 1990 1993 1996 1999 2002 10,000 transistors 150,000,000 transistors Leading edge chip in 1981 Leading edge chip in 2002

  37. Design of Embedded Systems (Wescon 1975) • “... avoid data processing aides such as assemblers, high-level languages, simulated systems, and control panels. These computer-aided design tools generally get in the way of cost-effective design and are more a result of the cultural influence of data processing, rather than a practical need.” • “bulk of real-world control problems require less than 2,000 instructions to implement. For this size of program computer aided design does little to improve the design approach and does a lot to separate the design engineer from intimate knowledge of his hardware.”

  38. Design needs Design technology Achieving the metrics + fast & reliably Enhanced productivity Design – single stage Multi stage - several abstraction levels

  39. Design Technology • The manner in which we convert our concept of desired system functionality into an implementation Compilation/ Synthesis Libraries/ IP Test/ Verification Compilation/Synthesis: Automates exploration and insertion of implementation details for lower level. System specification System synthesis Hw/Sw/ OS Model simulat./ checkers Hw-Sw cosimulators Behavioral specification Libraries/IP: Incorporates pre-designed implementation from lower abstraction level into higher level. Cores Behavior synthesis RT components HDL simulators RT specification RT synthesis Test/Verification: Ensures correct functionality at each level, thus reducing costly iterations between levels. Gate simulators Logic specification Gates/ Cells Logic synthesis To final implementation

  40. Compilation and synthesis Specify in abstract manner and get lower level details Libraries and IP - reusability Are ICs a form of libraries? How do cores differ from ICs Test / verification Simulation HDL based simulations

  41. Multiple perspectives for visualisation of a system Functionality perspective Environmental User I/F or Operator perspective System Performance Architectural perspective Physical

  42. Systematic Design of Embedded Systems • Most embedded systems are far too complex for Adhoc/empirical approach to design(100,000 lines) • Methodical, engineering-oriented, tool-based approach is essential • specification, synthesis, optimization, verification etc. • prevalent for hardware, still rare for software • One key aspect is the creation of models • Representation of knowledge and ideas about the system being developed - specification • Models only represent certain properties to be analyzed, understood & verified. They omit or modify certain details (abstraction) based on certain assumptions. One of the few tools available for dealing with complexity

  43. Abstractions and Models • Models are foundations of science and engineering • Designs usually start with informal specifications • However, soon a need for Models and Abstractions is established • Models or abstractions have connections to Implementation (h/w, s/w) and Application • Two types of modeling: System structure & system behavior • The relationships, behavior and interaction of atomic components • Coordinate computation of & communication between components • Models from classical CS • FSM, RAM (von Neumann), CCS (Milner) • Turing machine, Universal Register Machine

  44. Models Conceptual model Physical model Analogue model Mathematical model Numerical model Computational model Implementation Assumptions & accuracy

  45. Good Models • Simple • Ptolemy vs. Galileo • Amenable for development of theory to reason • should not be too general • Has High Expressive Power • a game is interesting only if it has some level of difficulty! • Provides Ability for Critical Reasoning • Science vs. Religion • Practice is currently THE only serious test of model quality • Executable (for Simulation) • Synthesizable • Unbiased towards any specific implementation (h/w or s/w)

  46. Modeling Embedded Systems • Functional behavior: what does the system do • in non-embedded systems, this is sufficient • Contract with the physical world • Time: meet temporal contract with the environment • temporal behavior important in real-time systems, as most embedded systems are • simple metric such as throughput, latency, jitter • more sophisticated quality-of-service metrics • Power: meet constraint on power consumption • peak power, average power, system lifetime • Others: size, weight, heat, temperature, reliability etc System model must support description of both functional behavior and physical interaction

  47. Elements of a Model of a Computation System: Language • Set of symbols with superimposed syntax & semantics • textual (e.g. matlab), visual (e.g. labview) etc. • Syntax: rules for combining symbols • well structured, intuitive • Semantics: rules for assigning meaning to symbols and combinations of symbols • without rigorous semantics, precise model behavior over time is not well defined • full executability and automatic h/w or s/w synthesis is impossible • E.g. operational semantics (in terms of actions of an abstract machine), denotational semantics (in terms of relations)

  48. Simulation and Synthesis • Two sides of the same coin • Simulation: scheduling then execution on desktop computer(s) • Synthesis: scheduling then code generation in C++, C, assembly, VHDL, etc. • Validation by simulation important throughout design flow • Models of computation enable • Global optimization of computation and communication • Scheduling and communication that is correct by construction

  49. Models Useful In Validating Designs • By construction • property is inherent. • By verification • property is provable. • By simulation • check behavior for all inputs. • By intuition • property is true. I just know it is. • By assertion • property is true. Would make something of it? • By intimidation • Don’t even try to doubt whether it is true • It is generally better to be higher in this list !

  50. An embedded system is expected to receive inputs, process data or information, and provide outputs The processing is done by processors Before we build the processor we must know the expected behaviour of the processor This is the model of the processor. We may call it a computational model. Before the processor is built it is in our mind. We express this model through a description - text, graphics, or some formal language

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