Writing Testbenches Functional Verification of HDL Models Second Edition

I will first introduce the necessary concepts and tools of verification, then I'll describe a process for planning and carrying out an effective functional verification of a design. I will also introduce the concept of coverage models that can be used in a coveragedriven verification process. It will be necessary to cover some VHDL and Verilog language semantics that are often overlooked or oversimplified in textbooks intent on describing the synthesizeable subset. These unfamiliar semantics become important in understanding what makes a wellimplemented and robust testbench and in providing the necessary control and monitor features. Once these new semantics are understood in a familiar language, the same semantics are presented in new verification-oriented languages. I will also present techniques for applying stimulus and monitoring the response of a design, by abstracting the physical-level transac-tions into high-level procedures using bus-functional models. The architecture of testbenches built around these bus-functional models is important to create a layer of abstraction relevant to the function being verified and to minimize development and maintenance effort. I also show some strategies for making testbenches selfchecking. Creating random testbenches involves more than calling the random() function in whatever language is used to implement them. I will show how random stimulus generators, built on top of busfunctional models, can be architected and designed to be able to produce the desired stimulus patterns. Random generators must be easily externally constrained to increase the likelihood that a set of interesting patterns will be generated. Behavioral modeling is another important concept presented in this book. It is used to parallelize the implementation and verification of a design and to perform more efficient simulations. For many, behavioral modeling is synonymous with synthesizeable or RTL modeling. In this book, the term "behavioral" is used to