Functional Verification of System on Chips-Practices, Issues and Challenges

摘要

System on Chip (SoC) designs inherit all the well known verification and validation difficulties associated with complex ASIC designs, besides adding their own set of newer problems. These arise because SoCs are primarily implemented by re-using Intellectual Property (IP) cores. It is well known that verification today constitutes about 70% to 80% of the total design effort, thereby, making it the most expensive component in terms of cost and time, in the entire design flow. It is expected to get even worse for SoC designs. In a complex SoC design flow functional verification is very important; any behavioral or functional bug escaping this phase will not be detected in the subsequent implementation phases and will surface only after the first silicon is integrated into the target system, resulting in costly design and silicon iterations. A number of academic and industrial research laboratories have been carrying out research on functional verification of SoCs based on different approaches. Partial success has been achieved in deploying them. Many of the issues relate to intrinsic limitations of some of the approaches taken; while others have to do with the quality of the design information, by way of, design descriptions, design documentations and design specifications, from which the overall verification objectives are derived. SoCs have brought to focus the need to carry out design and verification concurrently. For the design and verification task to proceed concurrently there is a need to capture formally, design information and implementation details at various levels of abstraction. Another reason for the need to formalize is that, as designs become more complex, functional verification will have to be carried out using the divide and conquer approach.We discuss several approaches based on compositional verification. For these approaches to succeed, specifications of either, the individual modules, or individual IPs, if any are used, have to be stated formally. There exist several commercialofferings addressing the area of SoC functional verification. Most of these use some form of divide and conquer approach related to compositional verification. The basis of success of some of these tools lies in the fact that the specifications of the IP cores are in essence captured in some executable form, be they formal specification languages, or commonly used HDLs suitably modified for the purpose.This tutorial is structured to provide information on the state of the art in the area of functional verification. It will focus on existing methodologies, tools, and practical approaches based on universal simulation, emulation, formal verification, and semi-formal verification that can be employed to overcome the SoC verification problem. We discuss a number of real life verification projects, describing the various techniques used and the effectiveness of these techniques. We conclude the tutorial by presenting issues, which form the current focus for research.