ch9-1 System Design..methodologies.pptVIP

yin yong System design techniques Design methodologies. Requirements and specification. Design methodologies (P.318) Process for creating a system. Many systems are complex: large specifications; multiple designers; interface to manufacturing. Proper processes improve: quality; cost of design and manufacture. Product metrics Time-to-market: beat competitors to market; meet marketing window (back-to-school). Design cost. Manufacturing cost. Quality. Mars Climate Observer Lost on Mars in September 1999. Requirements problem: Requirements did not specify units. Lockheed Martin used English; JPL wanted metric. Not caught by manual inspections. Design flow (P.319) Design flow: sequence of steps in a design methodology. May be partially or fully automated. Use tools to transform, verify design. Such as compiler, CAD. Design flow is one component of methodology. Methodology also includes management organization, etc. Waterfall model Early model for software development: Waterfall model steps Requirements: determine basic characteristics. Architecture: decompose into basic modules. Coding: implement and integrate. Testing: exercise and uncover bugs. Maintenance: deploy, fix bugs, upgrade. Waterfall model critique Only local feedback---may need iterations between coding and requirements, for example. Doesn’t integrate top-down and bottom-up design. Assumes hardware is given. Spiral model (P.320) Spiral model critique Successive refinement of system. Start with mock-ups, move through simple systems to full-scale systems. Provides bottom-up feedback from previous stages. Working through stages may take too much time. Successive refinement model Hardware/software design flow Co-design methodology Must architect hardware and software together: provide sufficient resources; avoid software bottlenecks. Can build pieces somewhat independently, but integration is major step. Also requires bottom-up feedback. Hierarchical design flow (P.321) Embedded systems must be designed ac