Building an open-source verification environment is not an easy or cheap task. It remains unclear who is willing to pay for it.
Brian Bailey, Semiconductor Engineering
September 2, 2020
Defining an open-source verification methodology is a lot more difficult than just developing an open-source simulator. This is the reality facing open-source hardware such as RISC-V. Some people may be asking for the corresponding open-source verification, but that is a much tougher problem — and it is not going to be solved in the short term.
Part one examined the reasons why open-source verificationmay make sense and the large amount of commercial software that is needed to do this today. This article will examine the role that various organization can play in the creation or support of a verification flow and the progress being made towards pieces of that becoming open-source.
It is useful to consider this in the context of RISC-V, because the infrastructure surrounding that is layered. Each layer has a role to play and adds something to the final development of a solution. At the top is RISC-V International, which defines the ISA and the extensions that are considered to be standard. The organization has a specific set of needs for verification. In addition, a number of consortiums, including lowRISC, OpenHW, OpenTitan, and Chips Alliance, are building open-source extensions to RISC-V or implementations of them that satisfy certain sets of requirements.
Myriad companies utilize the output of RISC-V or the consortiums to create custom implementations for people to integrate into their chips. Many of those companies also want open-source components for bus interfaces, memory subsystems, and more. Some companies, such as Western Digital, have developed implementations and have fed those back into the consortiums.
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Formal is certainly the preferred way to go for some companies. “Given the implementation transparency of open-source hardware, it is easier to employ white-box verification using formal verification such as property proving or equivalence checking,” says Bipul Talukdar, director of applications engineering for SmartDV in North America. “Formal methods from EDA companies may come with licensing complications, but those tools might be more useful compared to open resources because monetizing such a model would be a challenge and restrict widespread adoption. The solution could be opening up formal tool licensing mechanisms for third-party formal method development.”
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Conclusion
There is no open-source verification flow available today, and while some pieces are being worked on, it will be a long time before we can expect to see open-source verification tools with even close to the same levels of capabilities or performance as the commercial tools. While some may want tools that only have the capabilities required to verify a RISC-V core, most people then want to integrate that into a much larger system, and suddenly the cost of verification tools becomes less significant.
Bodies like RISC-V International are being realistic. “We’re trying to make sure that the ecosystem that enables people to do everything from device verification to debuggers to compilers and optimizers or middleware databases, and runtimes, interpreters and so on — they are all important. Our job is around the open-source piece, around the implementation independent piece. The stuff that we do is necessary, but not sufficient, for a customer or member to successfully create a solution for their customers.”
So far, few companies have shown a willingness to put up the necessary amount of money that it would take to create a suite of open-source verification tools. The best bet the industry has is within the Chips Alliance, and a lot of people are wishing them success. The EDA industry, meanwhile, remains on the fence.
“If you invest in technology, you have to innovate, you need to charge for it,” says Synopsys’ Vittal. “How can I give you an open-source tool and not charge for it and still come up with innovative technologies?”
McKellar agrees. “Everyone needs to be given a reasonable ability to make money, a reasonable markup, or things will collapse.”