Two groups of people are essential to a successful design project: a design team and a verification team. Designers usually have formal training from schools. Many colleges have comprehensive curricula on logic design, ranging from introduction to digital design to advanced computer architecture. On the contrary, most verification engineers learn their trade on the job; few were educated as verification engineers in academia, although many schools are beginning to teach verification curriculum. In fact, a majority of verification engineers started out as designers and gradually transitioned to design verification. Unlike design techniques and methodologies, a broad range of verification knowledge is loosely organized and informally acquired through hands-on experience. Furthermore, the horizon of verification has been expanding at a rapid pace: The verification landscape is evolving every six months with new techniques, standards, and tools. Nevertheless, there are principles and techniques that have survived the test of time and prove to be cornerstones of verification.
This book collects and organizes a wide range of digital design verification techniques and methodologies commonly used in industry and presents them in a systematic fashion. The focus of the book is on digital logic design and verification. It does not cover verification of circuits with mixed-signal or radio frequency components. A goal of the book is to pass the vast amount of verification knowledge to college students and engineers so that they are better prepared for the workforce, and to speed up their learning pace. It is tempting to write a ten-minute verification engineering book that lists detailed practical tips that can be used immediately on the job. These quick-fix tips often become obsolete over a short period of time. On the other hand, presenting the principles only will not be immensely useful for practicing engineers. Thus, I decided to strike a balance between the two and present verification principles as well as common practices. It is my belief that only by understanding the principles can one truly grasp the essence of the practices and be creative about using them.
One targeted audience for this book includes undergraduate students at the junior or senior level or first-level graduate students. I will assume that these readers have a sound understanding of a hardware descriptive language, preferably Verilog, because Verilog is used for illustration purposes in most parts of the book. In addition, a rudimentary knowledge of logic design is beneficial. This book is an introduction to design verification. Through its study, students will learn the main ideas, tools, and methodologies used in simulation-based verification, and the principles behind formal verification. The materials presented are industry tested and widely used. At the end of each chapter, problems are presented as a means of refreshing the knowledge covered in the chapter. For those who want to explore certain topics in more depth, please refer to the citations listed in the bibliography.
The other targeted audience includes verification professionals who may have some verification experience but would like to get a systematic overview of the different areas in verification and an understanding of the basic principles behind formal verification. The prerequisites for this audience are similar to those for the first group: basic design knowledge and a hardware descriptive language. The first part of the book provides a comprehensive treatment of simulation-based verification methodology and serves as a refresher or an introduction to verification professionals. For many practicing engineers, formal verification tools appear to be a form of black magic that requires a doctorate in mathematics to comprehend. This book explains these tools and the working principles of formal verification. Before formal verification is discussed in depth, Chapter 7 reviews the basics of mathematics and computer algorithms required to understand verification algorithms fully.
As with every technology, there is no substitution for hands-on experience. I encourage you to get acquainted with verification tools by running some of the examples and problems in the book or designing a project that makes use of the tools described. Free CAD tools such as Verilog simulator, test bench development aid, and waveform viewer are available at www.verilog.net/free.html.
This book is comprised of two parts. The first part addresses the conventional verification strategy—simulation-based verification—whereas the second part addresses the aspects of formal verification that are well established in academia and tested in industry. The two parts are self-contained and thus can be taught independently as deemed fit.
The first part describes many verification tools. Because the specifics of these tools differ from vendor to vendor and change from time to time, only pseudo common commands are used in this book. To reinforce learning these tools, I recommend that industrial tools be part of a verification laboratory (for instance, a simulator, a waveform viewer, a coverage tool, a bug tracking system, and a revision control system). Similarly, to solidify the knowledge of formal verification, commercial formal verification tools such as an HDL linter, a model checker, and an equivalence checker should be used during lab sessions.
This book has a companion instructor’s manual that contains the solutions to all the problems at the end of each chapter. The instructor’s manual is available on request to the publisher.
Again, this book is intended as an introduction to design verification. I will assume that you have an understanding of basic Verilog constructs. Even though the book is written using Verilog as the hardware description language, I made an effort to present ideas independent of Verilog. When the use of Verilog is unavoidable, the simplest Verilog constructs are used to allow readers unfamiliar with the language to grasp the main ideas.
As previously stated, this book consists of two parts. The first part is devoted to simulation-based verification and the second part discusses formal verification. Simulation-based verification is by far the most widely used methodology and is a necessary requirement for all verification engineers. Formal verification is a relatively new technology and it complements simulation-based verification. I believe that to utilize a technology best, one must first be equipped with an in-depth understanding of the internal working principles of that technology. As a result, instead of just studying a verification tool’s operations at the user level—a topic better suited for user manuals—this book spends much time studying the fundamental principles of simulation and formal technology.
The first part—simulation technology—consists of Chapters 2 through 6, and these chapters are ordered similar to the usual sequence of operations encountered during a simulation verification process. We start with Chapter 2, checking for static errors. These are errors that can be detected without input vectors and must be eliminated before extensive simulation begins. In Chapter 3, we study the basic architectures of simulators. Event-driven and cycle-based simulation algorithms are presented first, followed by simulator operations and applications for which we discuss cosimulation, design profiling, common simulator options, and the user interface.
Before one can begin a simulation, one must construct a test bench to host the design. Chapter 4 discusses test bench design, initialization, stimuli generation, clock network, error injection, result assessment, and test configuration. After a design is free of static errors and is embedded in a test bench, it is ready to be simulated. But how should the design be simulated? Chapter 5 addresses the issues of what to simulate and how to measure the quality of the simulation. We will look at test plan design, generation of tests for the items in the test plan, output response assessment, assertion (particularly, System Verilog assertions), and verification coverage.
After a circuit is simulated and the bugs are discovered, the next step is to debug problems found during simulation. Chapter 6 presents widely used debugging techniques, including case reduction, check pointing, error tracing, trace dumping, and forward and backward debugging. In addition, Chapter 6 examines the four basic views of design: source code, schematic, waveform, and finite-state machine. We then examine the scenario after the bugs are fixed. The tools and methodology discussed include the revision control system, regression mechanism, and tape-out criteria.
The second part of the book—formal verification—consists of Chapters 7 through 9. Several chapters in the first part of the book can be studied in conjunction with the second. For example, Chapters 2, 4, 5, and 6 are also applicable to formal verification.
The key to understanding formal verification lies in an understanding of the theory behind it. Chapter 7 provides the basic mathematical background for the later chapters. The materials cover Boolean functions and representations, symmetric Boolean functions, finite-state machines and the equivalence algorithm, and graphic algorithms such as depth-first search and breadth-first search, and strongly connected components.
Chapter 8 presents a survey of decision diagrams, with an emphasis on binary decision diagrams. We then review SAT (satisfiability) as an alternative to decision diagrams. The chapter concludes with a look at applications of decision diagrams and SAT in equivalence checking and symbolic simulation.
Chapter 9 presents an in-depth study of symbolic model checking. First it presents automata and computational tree logic as a means of modeling temporal behavior with fairness constraints. It then discusses algorithms for checking a model against a temporal specification. Based on the model-checking algorithms, efficient symbolic model-checking algorithms are presented in which graphical operations are accomplished through Boolean function computations. Next, equivalence checking is revisited for general circuits for which one-to-one state correspondence does not exist. To conclude, algorithms for better managing symbolic computation are studied.
A book of this size is bound to have errors and areas for improvement. Please report errors and send comments to the author at [email protected].
