Introduction to Embedded System Xiaoming JU 2005.2

1. Introduction to Embedded System Xiaoming JU 2005.2

2. Introduction • What are embedded systems? • Challenges in embedded system design. • Design methodologies. Introduction to Embedded Systems

3. Definition • What is a real-time system? • “A real-time computer system may be defined as one which controls an environment by receiving data, processing them, and returning the results sufficiently quickly to affect the environment at the time” • “Pertaining to processing of data by a computer in connection with another process outside the computer according to time requirements imposed by the outside process” • What is an embedded system? • “Anything that uses a computer but does not look like one” • “The microprocessor in an embedded system is like an electric motor in a washing machine” • “An Embedded system means the real-time software is a component of a larger HW/SW system” Introduction to Embedded Systems

4. output analog input CPU analog mem embedded computer Embedding a computer Embedded Systems are quite diverse, no one statementdescribes them all Introduction to Embedded Systems

5. Auxililary systems Memory FPGA/ASIC From: Diagnostic port Human Interface Koopman, P., Embedded System Desing A/D CPU D/A Conversion Issues - The Conversion rest of the Story, Proc of 1996 CCD SENSORS Electromechanical backup & safety Actuators External Environment Introduction to Embedded Systems

6. Products with Embedded Systems ? • Of 4 billions microprocessors/microcontrollers sold per year, 95% are for embedded products: • VCRs, DVD players • Cell phone • Microwave • Washer • Camera • Cars (antilock brake system, air-bag, gas injection, electricity distribution..) • Printers, copiers • ……… Introduction to Embedded Systems

7. Early history • Late 1940’s: MIT Whirlwind computer was designed for real-time operations. • Originally designed to control an aircraft simulator. • 1971: Intel 4004, first microprocessor (4bits), initially for a calculator. • Microprocessors get so cheap that microprocessor-based control systems become the rule. • Only limit: processing time.c Introduction to Embedded Systems

8. Microprocessor varieties • Microcontroller: includes I/O devices, on-board memory. • Digital signal processor (DSP): microprocessor optimized for digital signal processing. • Typical embedded word sizes: 8-bit, 16-bit, 32-bit. Introduction to Embedded Systems

9. Application examples • Canon EOS 3 camera has three microprocessors. • One of 32-bit RISC CPU runs autofocus and eye control systems. • Digital TV: programmable CPUs + hardwired logic. • Today’s high-end automobile may have 100 microprocessors: • 4-bit microcontroller checks seat belt; • microcontrollers run dashboard devices; • 16/32-bit microprocessor controls engine. Introduction to Embedded Systems

10. BMW 850i brake and stability control system • Anti-lock brake system (ABS): pumps brakes to reduce skidding. • Automatic stability control (ASC+T): controls engine to improve stability. • ABS and ASC+T communicate. • ABS was introduced first---needed to interface to existing ABS module. Introduction to Embedded Systems

11. BMW 850i, cont’d. sensor sensor brake brake hydraulic pump ABS brake brake sensor sensor Introduction to Embedded Systems

12. Characteristics of embedded systems • Single function (dedicated to a specific task). • Tightly constrained based on design metrics such as. • Cost • Size • Power • Performance • Real time constraints • A wide verity of embedded processors and processor architectures are available. • May not have an operating system if it does it is probably a real time operating system (RTOS). Introduction to Embedded Systems

13. Real-time operation • Must finish operations by deadlines. • Hard real time: missing deadline causes failure. • Soft real time: missing deadline results in degraded performance. • Many systems are multi-rate: must handle operations at widely varying rates. Introduction to Embedded Systems

14. Why use microprocessors? • Alternatives: field-programmable gate arrays (FPGAs), custom logic, etc. • Microprocessors are often very efficient: can use same logic to perform many different functions. • Microprocessors simplify the design of families of products. Introduction to Embedded Systems

15. The performance paradox • Microprocessors use much more logic to implement a function than does custom logic. • But microprocessors are often at least as fast: • heavily pipelined; • large design teams; • aggressive VLSI technology. Introduction to Embedded Systems

16. Power • Custom logic is a clear winner for low power devices. • Modern microprocessors offer features to help control power consumption. • Software design techniques can help reduce power consumption. Introduction to Embedded Systems

17. 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: the amount of power consumed by the system • Flexibility: the ability to change the functionality of the system without incurring heavy NRE cost Introduction to Embedded Systems

18. Challenges, etc. • 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 Introduction to Embedded Systems

19. Challenges, etc. • 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 Introduction to Embedded Systems

20. SGS-Thomson Videophone DSP core 1 (ST18950): modem VLIW DSP: Programmable video operations std. extensions A/D & D/A DSP core 1 (ST18950): Sound codec High-speed H/W: Video operators for DCT, inv. DCT, motion estimation MCU 1 (ASIP): Master control Memory: Video RAM Glue logic MCU 2 (ASIP): Mem. Controller I/O: Serial interface Hardware Embedded Real-time Software MCU 3 (ASIP): Bit manip. I/O: Host interface The next design challenge: SoC • System-on-chip (SoC) • prefabricated components: IP cores • great importance of software • How do you design such systems? • Mostly done in an ad-hoc-fashion Introduction to Embedded Systems

21. How do you design embedded system? • Classical water-fall model: • Requirements specification: • Determine what the client wants • Analysis: • Determine what needs to be done • Ideally we would have an executable specification of the system • Design: • Determine how the analysis result should be implemented • Come up with an implementation plan • Implementation: • Coding • Testing: • Determine that the implementation is what needed to be done Introduction to Embedded Systems

22. Throughput Response Testability Low power Reliability Safety Maintainability Security Availability Cost Size/Weight Survivability Required Features for Embedded System Introduction to Embedded Systems

23. Design methodologies • A procedure for designing a system. • Understanding your methodology helps you ensure you didn’t skip anything. • Compilers, software engineering tools, computer-aided design (CAD) tools, etc., can be used to: • help automate methodology steps; • keep track of the methodology itself. Introduction to Embedded Systems

24. requirements Top-down specification Bottom-up architecture component design system integration Levels of abstraction Introduction to Embedded Systems

25. Top-down vs. bottom-up • Top-down design: • start from most abstract description; • work to most detailed. • Bottom-up design: • work from small components to big system. • Real design uses both techniques. Introduction to Embedded Systems

26. Stepwise refinement • At each level of abstraction, we must: • analyze the design to determine characteristics of the current state of the design; • refine the design to add detail; • ensure all design objects. Introduction to Embedded Systems

27. Requirements • Plain language description of what the user wants and expects to get. • May be developed in several ways: • talking directly to customers; • talking to marketing representatives; • providing prototypes to users for comment. Introduction to Embedded Systems

28. Functional vs. non-functional requirements • Functional requirements: • output as a function of input. • Non-functional requirements: • time required to compute output; • size, weight, etc.; • power consumption; • reliability; • etc. Introduction to Embedded Systems

29. Our requirements form Introduction to Embedded Systems

30. I-78 Scotch Road Current position Display position lat: 40°13′ lon: 32°19′ Example: GPS moving map requirements • Moving map obtains position from GPS, paints map from local database. Introduction to Embedded Systems

31. GPS moving map needs • Functionality: For automotive use. Show major roads and landmarks. • User interface: At least 400 x 600 pixel screen. Three buttons max. Pop-up menu. • Performance: Map should scroll smoothly. No more than 1 sec power-up. Lock onto GPS within 15 seconds. • Cost: $500 street price = approx. $100 cost of goods sold. • Physical size/weight: Should fit in hand. • Power consumption: Should run for 8 hours on four AA batteries. Introduction to Embedded Systems

32. GPS moving map requirements form Introduction to Embedded Systems

33. Specification • A more precise description of the system: • should not imply a particular architecture; • provides input to the architecture design process. • May include functional and non-functional elements. • May be executable or may be in mathematical form for proofs. Introduction to Embedded Systems

34. GPS specification • Should include: • What is received from GPS; • map data; • user interface; • operations required to satisfy user requests; • background operations needed to keep the system running. Introduction to Embedded Systems

35. Architecture design • What major components go satisfying the specification? • Hardware components: • CPUs, peripherals, etc. • Software components: • major programs and their operations. • Must take into account functional and non-functional specifications. Introduction to Embedded Systems

36. display GPS receiver search engine renderer database user interface GPS moving map block diagram Introduction to Embedded Systems

37. display frame buffer CPU GPS receiver memory panel I/O GPS moving map hardware architecture Introduction to Embedded Systems

38. database search renderer pixels position user interface timer GPS moving map software architecture Introduction to Embedded Systems

39. GPS Introduction to Embedded Systems

40. Designing hardware and software components • Must spend time architecting the system before you start coding. • Some components are • ready-made, • some can be modified from existing designs, • others must be designed from scratch. Introduction to Embedded Systems

41. System integration • Put together the components. • Many bugs appear only at this stage. • Have a plan for integrating components to uncover bugs quickly, test as much functionality as early as possible. Introduction to Embedded Systems

42. Thank you Introduction to Embedded Systems