Harry D. Foster

Principles of Verifiable RTL Design: A Functional Coding Style Supporting Verification Processes in Verilog explains how you can write Verilog to describe chip designs at the RT-level in a manner that cooperates with verification processes. This cooperation can return an order of magnitude improvement in performance and capacity from tools such as simulation and equivalence checkers. It reduces the labor costs of coverage and formal model checking by facilitating communication between the design engineer and the verification engineer. It also orients the RTL style to provide more useful results from the overall verification process. The intended audience for Principles of Verifiable RTL Design: A Functional Coding Style Supporting Verification Processes in Verilog is engineers and students who need an introduction to various design verification processes and a supporting functional Verilog RTL coding style. A second intended audience is engineers who have been through introductory training in Verilog and now want to develop good RTL writing practices for verification. A third audience is Verilog language instructors who are using a general text on Verilog as the course textbook but want to enrich their lectures with an emphasis on verification. A fourth audience is engineers with substantial Verilog experience who want to improve their Verilog practice to work better with RTL Verilog verification tools. A fifth audience is design consultants searching for proven verification-centric methodologies. A sixth audience is EDA verification tool implementers who want some suggestions about a minimal Verilog verification subset. Principles of Verifiable RTL Design: A Functional Coding Style Supporting Verification Processes in Verilog is based on the reality that comes from actual large-scale product design process and tool experience.

System designers, computer scientists and engineers have c- tinuously invented and employed notations for modeling, speci- ing, simulating, documenting, communicating, teaching, verifying and controlling the designs of digital systems. Initially these s- tems were represented via electronic and fabrication details. F- lowing C. E. Shannon’s revelation of 1948, logic diagrams and Boolean equations were used to represent digital systems in a fa- ion that de-emphasized electronic and fabrication detail while revealing logical behavior. A small number of circuits were made available to remove the abstraction of these representations when it was desirable to do so. As system complexity grew, block diagrams, timing charts, sequence charts, and other graphic and symbolic notations were found to be useful in summarizing the gross features of a system and describing how it operated. In addition, it always seemed necessary or appropriate to augment these documents with lengthy verbal descriptions in a natural language. While each notation was, and still is, a perfectly valid means of expressing a design, lack of standardization, conciseness, and f- mal definitions interfered with communication and the understa- ing between groups of people using different notations. This problem was recognized early and formal languages began to evolve in the 1950s when I. S. Reed discovered that flip-flop input equations were equivalent to a register transfer equation, and that xvi tor-like notation. Expanding these concepts Reed developed a no- tion that became known as a Register Transfer Language (RTL).

There is much excitement in the design and verification community about assertion-based design. The question is, who should study assertion-based design? The emphatic answer is, both design and verification engineers. What may be unintuitive to many design engineers is that adding assertions to RTL code will actually reduce design time, while better documenting design intent. Every design engineer should read this book! Design engineers that add assertions to their design will not only reduce the time needed to complete a design, they will also reduce the number of interruptions from verification engineers to answer questions about design intent and to address verification suite mistakes. With design assertions in place, the majority of the interruptions from verification engineers will be related to actual design problems and the error feedback provided will be more useful to help identify design flaws. A design engineer who does not add assertions to the RTL code will spend more time with verification engineers explaining the design functionality and intended interface requirements, knowledge that is needed by the verification engineer to complete the job of testing the design.

Assertion-based IP is much more than a comprehensive set of related assertions. It is a full-fledged reusable and configurable transaction-level verification component, which is used to detect both interesting and incorrect behaviors. Upon detecting interesting or incorrect behavior, the assertion-based IP alerts other verification components within a simulation environment, which are responsible for taking appropriate action. The focus of this book is to bring the assertion discussion up to a higher level and introduce a process for creating effective, reusable, assertion-based IP, which easily integrates with the user’s existing verification environment, in other words the testbench infrastructure. The guiding principles promoted in this book when creating an assertion-based IP monitor are: modularity—assertion-based IP should have a clear separation between detection and actionclarity—assertion-based IP should be written initially focusing on capturing intent (versus optimizations) A unique feature of this book is the fully worked out, detailed examples. The concepts presented in the book are drawn from the authors’ experience developing assertion-based IP, as well as general assertion-based techniques. Creating Assertion-Based IP is an important resource for design and verification engineers. From the Foreword: Creating Assertion-Based IP "…reduces to process the creation of one of the most valuable kinds of VIP: assertion-based VIP…This book will serve as a valuable reference for years to come."Andrew Piziali, Sr. Design Verification EngineerCo-Author, ESL Design and Verification: A Prescription for Electronic System Level MethodologyAuthor, Functional Verification Coverage Measurement and Analysis

Chapter 3 Specifying RTL Properties 61 3. 1 Definitions and concepts 62 62 3. 1. 1 Property 3. 1. 2 Events 65 3. 2 Property classification 65 Safety versus liveness 66 3. 2. 1 3. 2. 2 Constraint versus assertion 67 3. 2. 3 Declarative versus procedural 67 3. 3 RTL assertion specification techniques 68 RTL invariant assertions 69 3. 3. 1 3. 3. 2 Declaring properties with PSL 72 RTL cycle related assertions 73 3. 3. 3 3. 3. 4 PSL and default clock declaration 74 3. 3. 5 Specifying sequences 75 3. 3. 6 Specifying eventualities 80 3. 3. 7 PSL built-in functions 82 3. 4Pragma-based assertions 82 3. 5 SystemVerilog assertions 84 3. 5. 1 Immediate assertions 84 3. 5. 2Concurrent assertions 86 3. 5. 3 System functions 95 3. 6 PCI property specification example 96 3. 6. 1 PCI overview 96 3. 7 Summary 102 Chapter 4 PLI-Based Assertions 103 4. 1 Procedural assertions 104 4. 1. 1 A simple PLI assertion 105 4. 1. 2 Assertions within a simulation time slot 108 4. 1. 3 Assertions across simulation time slots 111 4. 1. 4 False firing across multiple time slots 116 4. 2 PLI-based assertion library 118 4. 2. 1 Assert quiescent state 119 4. 3 Summary 123 Chapter 5 Functional Coverage 125 5. 1 Verification approaches 126 5. 2 Understanding coverage 127 5. 2. 1 Controllability versus observability 128 5. 2.

Assertion-based IP is much more than a comprehensive set of related assertions. It is a full-fledged reusable and configurable transaction-level verification component, which is used to detect both interesting and incorrect behaviors. Upon detecting interesting or incorrect behavior, the assertion-based IP alerts other verification components within a simulation environment, which are responsible for taking appropriate action. The focus of this book is to bring the assertion discussion up to a higher level and introduce a process for creating effective, reusable, assertion-based IP, which easily integrates with the user’s existing verification environment, in other words the testbench infrastructure. The guiding principles promoted in this book when creating an assertion-based IP monitor are: modularity—assertion-based IP should have a clear separation between detection and actionclarity—assertion-based IP should be written initially focusing on capturing intent (versus optimizations) A unique feature of this book is the fully worked out, detailed examples. The concepts presented in the book are drawn from the authors’ experience developing assertion-based IP, as well as general assertion-based techniques. Creating Assertion-Based IP is an important resource for design and verification engineers. From the Foreword: Creating Assertion-Based IP "…reduces to process the creation of one of the most valuable kinds of VIP: assertion-based VIP…This book will serve as a valuable reference for years to come."Andrew Piziali, Sr. Design Verification EngineerCo-Author, ESL Design and Verification: A Prescription for Electronic System Level MethodologyAuthor, Functional Verification Coverage Measurement and Analysis

Chapter 3 Specifying RTL Properties 61 3. 1 Definitions and concepts 62 62 3. 1. 1 Property 3. 1. 2 Events 65 3. 2 Property classification 65 Safety versus liveness 66 3. 2. 1 3. 2. 2 Constraint versus assertion 67 3. 2. 3 Declarative versus procedural 67 3. 3 RTL assertion specification techniques 68 RTL invariant assertions 69 3. 3. 1 3. 3. 2 Declaring properties with PSL 72 RTL cycle related assertions 73 3. 3. 3 3. 3. 4 PSL and default clock declaration 74 3. 3. 5 Specifying sequences 75 3. 3. 6 Specifying eventualities 80 3. 3. 7 PSL built-in functions 82 3. 4Pragma-based assertions 82 3. 5 SystemVerilog assertions 84 3. 5. 1 Immediate assertions 84 3. 5. 2Concurrent assertions 86 3. 5. 3 System functions 95 3. 6 PCI property specification example 96 3. 6. 1 PCI overview 96 3. 7 Summary 102 Chapter 4 PLI-Based Assertions 103 4. 1 Procedural assertions 104 4. 1. 1 A simple PLI assertion 105 4. 1. 2 Assertions within a simulation time slot 108 4. 1. 3 Assertions across simulation time slots 111 4. 1. 4 False firing across multiple time slots 116 4. 2 PLI-based assertion library 118 4. 2. 1 Assert quiescent state 119 4. 3 Summary 123 Chapter 5 Functional Coverage 125 5. 1 Verification approaches 126 5. 2 Understanding coverage 127 5. 2. 1 Controllability versus observability 128 5. 2.

System designers, computer scientists and engineers have c- tinuously invented and employed notations for modeling, speci- ing, simulating, documenting, communicating, teaching, verifying and controlling the designs of digital systems. Initially these s- tems were represented via electronic and fabrication details. F- lowing C. E. Shannon’s revelation of 1948, logic diagrams and Boolean equations were used to represent digital systems in a fa- ion that de-emphasized electronic and fabrication detail while revealing logical behavior. A small number of circuits were made available to remove the abstraction of these representations when it was desirable to do so. As system complexity grew, block diagrams, timing charts, sequence charts, and other graphic and symbolic notations were found to be useful in summarizing the gross features of a system and describing how it operated. In addition, it always seemed necessary or appropriate to augment these documents with lengthy verbal descriptions in a natural language. While each notation was, and still is, a perfectly valid means of expressing a design, lack of standardization, conciseness, and f- mal definitions interfered with communication and the understa- ing between groups of people using different notations. This problem was recognized early and formal languages began to evolve in the 1950s when I. S. Reed discovered that flip-flop input equations were equivalent to a register transfer equation, and that xvi tor-like notation. Expanding these concepts Reed developed a no- tion that became known as a Register Transfer Language (RTL).