This summer, the project and funding that led to the creation of the OpenRoad open-source RTL-to-GDS toolchain draws to a close. In 2018, US defense research agency DARPA backed the development of the tools as part of the IDEA program managed off by ZeroASIC founder Andreas Oloffson during his time at the organization.
Over the four years, OpenRoad has gained traction in some communities, along with a variety of other open-source projects, such as Verilator, which has received renewed attention from RISC-V work. A key target of IDEA and the IP-focused POSH was military R&D and the DEVCOM Army Research Laboratory has employed OpenRoad in some of its projects.
More widely, there are lingering concerns about the compatibility of open-source and commercial legal agreement. Some such as the MIT license are easy to deal with
“I’ve never seen a contract that’s so short,” said Oloffson during a conference panel on open-source EDA at DAC in San Francisco last week.
Others raise issues of ‘infection’ where it becomes impossible to use both commercial and open-source components without using one in some instances breaching the terms of the other. A key issue is what IP needs to be released to the community once an open-source component has been integrated, although this may be a larger problem in open-source hardware rather than EDA tools. Proponents point to the growing acceptance of open source within the software domain and the eager participation of companies who once favoured purely proprietary offerings. Without this widespread backing, the data-center market that is now so important to high-end chip development would probably not look nearly so lucrative to hardware designers.
Chips Alliance general manager Rob Mains noted in a DAC Pavilion panel: “You have to be very careful to pay attention to the license agreements, which is not something the average engineer pays attention to.”
However, for Peter Gadfort’s small team at DEVCOM Army Research Laboratory, OpenRoad’s licensing is considerably easier to deal with than those for proprietary tools. “We are just three people working on energy-efficient, trusted, reconfigurable computing. We also get to act as mini-lawyers, which can be painful,” he explained.
A major issue is the now common use of time-limited licensing. “That can leave us without tools for a long time. And it is often difficult to get licence periods to match project time.
“Open source helps us do research to help the customer: the Department of Defense. Using more of the outcomes from IDEA and POSH like OpenRoad lets us iterate faster. We are currently working on taping out to Intel 16 using OpenRoad. The level of integration we are aiming at is just not practical in a closed-source environment. And we dont have to worry about licence issues,” said Gadfort.
It was not entirely smooth-sailing, Gadfort added. “When we started using open-source tools, the documentation was a challenge. But we were able to give feedback and make things more user friendly. Coexistence with commercial tools is truly viable, which is important as a lot of EDA flows pingpong in and out of tools.”
Mix and match
Though they won’t replace all tools in a flow, at least not in the foreseeable future, commercial chip-design teams see clear benefits in the open-source approach around collaboration. Mamta Bansal, senior director of engineering at Qualcomm, said: “Open source has the potential to lower the barrier to contribute, customise and differentiate. Can draw parallels with other open source. Very possible for all of us to contribute to the EDA community.”
Noel Menezes, director of strategic CAD at Intel Labs, questioned whether the incentives are in place to make open-source EDA viable long-term. “There has to be a virtuous cycle that establishes itself.”
Open-source EDA tools are far from new though as SPICE was developed before the copyleft licensing associated with free and open-source software (FOSS) it lacks the association. The prior heyday of such open-source software was in the 1980s, Menezes said. “But the incentives went away.”
“Now, post-IDEA, it’s better again. OpenRoad has been very successful. But my fear is that if you don’t have incentives to continue open sourcing now it’s reaching the end of its four-year program, that will be a problem,” Menezes added.
Oloffson said people working on open-source projects need to “check in for the long road. There is a lifetime of open-source maintenance to be done: Verilator is now over 20 years old.”
Chuck Alpert, senior software group director at Cadence Design Systems, said: “At the end of the day, academic culture just isn’t suited for this.”
Alpert explained the pressure to publish novel experiments does not mix well with the need to continue long-term, incremental work on software. On top of that, he noted, “academic-tenure culture doesn’t really foster a team spirit. I think that’s a big challenge”.
At the same time, open-source will be invaluable to the academic pipeline into industry, Alpert said: “This has to happen. The biggest value of open source is talent creation. The people who aren’t just going to run to the Facebooks and Googles: OpenRoad is training them. We want those people. We need people trained in EDA and living it so they ultimately can become our future leaders.”
Commercial interest will be vital if long-term academic support is hard to envisage. Gadfort said the open-source ecosystem needs sustainable business models. “If they are to succeed, companies need a viable path to generate income as well as foundry support.”
Menezes argued open-source projects need not try to do everything in the flow and would probably be more successful by not attempting to compete head-on. He said he favors the relatively new area of domain-specific languages (DSLs). “You have to come up with some disruptive complementary ideas. DSL may be the right disruptor for open-source EDA. [The EDA industry] continues to solve some big problems. I would not recommend open-source to go there.”
One reason for seeing DSL as a potential winner for open source is that it is an area that provides a way to optimize the code and architecture of accelerators, which are increasingly becoming the engines of high-performance computing. The wide variety of architectures and software inputs provides good reasons for seeing ecosystems build around open-source tools that bring the software and hardware elements together and allow co-operative experimentation. Bansal said the ability, in general, to go into the tools to try different things will be invaluable. “We need a playground. We don’t have that today. Open source gives you that playground if structured the right way.”