FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Topics n Design methodologies.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Design methodologies n Every company has its own design methodology. n Methodology depends on: –size of chip; –design time constraints; –cost/performance; –available tools.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Design teams n Almost all interesting projects are too big for one person to handle. n Need a team of people with varying skills. n Who is in charge?

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Documents n Documents are critical: –Writing it helps you decide what to do. –Minimizes risk of hit-by-a-truck syndrome. –Provides information for maintenance, next generation. n Each document serves as the contract between the provider of the document and the consumer of the document.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Major documents n Requirements. n Specification. n Architecture. n Module designs. n Reference manual, user manual.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Types of information n Functional description. n Non-functional description: cycle time, power, etc. n Timetables. n Design verification methods. n Quality metrics. n Job assignments.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Starting the project n Requirements: English description of what is to be done. –Customer-oriented. –High-level. n May be written by marketing. n Author of requirements should verify that the requirements are accurate.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Specifications n The specification is the contract between marketing and the design team. n The specification is more technical than the requirements: –delays, etc. n An ideal specification would contain no architectural information, but that goal may be hard to achieve in practice. –The specification says what to do, not how to do it.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Specification and planning n Driven by contradictory impulses: –customer-centric concerns about cost, performance, etc.; –forecasts of feasibility of cost and performance. n Features, performance, power, etc. may be negotiated at early stages; negotiation at later stages creates problems.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Architecture n The architecture document is the contract between the system designers and the component designers. n Specifies major subsystems and their interactions. n Makes important design decisions. n Isn’t a full implementation.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Module designs n Specifies details of a module: –functionality; –non-functional parameters; –design verification.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Do documents reflect the product? n In a word, no. –Things change. –People don’t have time to conform documents to the final design. n Some amount of updating is important for maintenace, future generations.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Design reviews n Have other designers (team + non-team) evaluate a design. –Relatively simple. –Proven to work. n Must walk through the design in detail to look for problems, improvements.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Generic design flow architectural simulation Timing/area budget register-transfer design logic design physical design Final design verification detailed specs configuration

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Estimation and planning n Estimation techniques vary with module: –memories may be generated once size is known; –data paths may be estimated from previous design; –controllers are hard to estimate without details. n Estimates must include speed, area, power.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Floorplanning and budgeting n Want some early physical design information: area, delay, power, etc. n Ways to get info: –previous designs; –quick design runs.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Architecture n Need to build an executable model of the architecture. –Run vectors on architecture. –Use as golden design for comparison with later stages. n Modeling languages: –C: easier to write, less detailed. –Verilog: harder to write, synthesizable with effort.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Logic design n For controllers, good state assignment is usually requires CAD tools. n Logic synthesis is an option: –very good for non-critical logic; –can work well for speed-critical logic. n Logic synthesis system may be sensitive to changes in the input specification.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Place and route n Most computationally expensive stage. n Metrics take more time to judge than functional vectors. n Deciding how to fix a problem may take effort. –How to change placement, etc.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Design verification n Functional verification: –runs reasonable set of vectors. n Non-functional verification: –performance; –power.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Functional verification n At all levels of hierarchy: module, subsystem, system. n At every level of abstraction. –Compare to previous level of abstraction, golden model. n Must check interfaces. –Half of bugs are at the interface to other modules.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Functional verification input n Sources of vectors: –Previous designs. –Vectors from higher levels of abstraction. –Vectors designed previously for this stage. –Inputs from other modules.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Non-functional verification n Performance: –Static timing analysis. n Power: –Some information from timing analysis. –Power analysis tools.

FPGA-Based System Design: Chapter 6 Copyright  2004 Prentice Hall PTR Breadboards n May build a board to test an FPGA-based design. –Takes some time. –May allow running the design against the real I/O device.