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Open constraint format sparks new EDA standards discussion

Posted: 09 May 2007 ?? ?Print Version ?Bookmark and Share

Keywords:EDA standards? open constraint format? Synopsys Interoperability Forum?

The recent Synopsys Interoperability Forum offered the first public view into what may become the newest EDA standards effortan open analog constraint format.

Seeking a new level of interoperability for analog and custom IC design tools, speakers from Ciranova, Pulsic and Silicon Canvas called for a vendor-neutral constraint format that works with the OpenAccess database. Most of the discussion centered on analog layout constraints such as alignment and orientation, symmetry, differential pairs and shielding. Each vendor today has its own way for users to specify these constraints, leading to a hodgepodge of ad hoc formats and a lot of translation.

Ed Lechner, director of product marketing for analog/mixed-signal at Synopsys Inc., described the effort as an "offshoot" of the interoperable p-cell library initiative announced in April by Applied Wave Research, Ciranova, Silicon Canvas, Silicon Navigator and Synopsys. Speakers were invited to the Synopsys forum "because we thought it was a good opportunity to get the message out," Lechner said.

An open constraint format is needed so analog IC design tools can work together, Lechner said. "Right now, if there's an optimizer like we have in HSpice, an engineer has to reenter all the constraints he had for previous tools," he said. "It's a lot of rework and it's a hurdle to adoption of sophisticated analog tools."

"We have to have a way to translate information between tools consistently, easily and automatically," said Steve Ferguson, technical director for custom IC layout vendor Pulsic Inc. "An ad hoc approach is not going to work."

Dave Millman, VP of marketing at Ciranova, noted that analog designers have a common database with OpenAccess, but constraints are still driven by a limited number of tools. Ultimately, the result could be closed constraints, tools that won't work in an integrated flow and "broken OpenAccess flows," Millman said.

There's a lot of innovation under way in analog layout, said Richard Morse, director of marketing at Silicon Canvas Inc. "If we fail to provide an open constraint environment, or we allow it to be defined by a single vendor, we will stifle a lot of this innovation."

Gary Smith, chief analyst at Gary Smith EDA, noted that analog and custom design is Cadence Design Systems Inc.'s last "franchise" area. "There is an obvious need for an upgrade in today's analog methodology and tools," he said. "An open constraint format would go a long way in advancing today's analog layout tools."

As the main provider of analog IC layout tools, Cadence's view on a prospective constraint standard would be crucial. Anthony Gadient, group director for product marketing at Cadence, said his company thinks it's too early, given that constraint-driven analog flows are just emerging. Cadence last fall rolled out the first version of its Virtuoso layout system, which provides a unified set of constraints across the IC design flow.

'Open to all tools'
The call for an open analog constraint format has come to the attention of the Silicon Integration Initiative (Si2) OpenAccess Coalition, said Nick English, Si2 VP of development. But no formal technology request has been made, and the coalition needs to better understand how analog constraints could be added to OpenAccess, he said.

In his presentation at the Synopsys forum, Millman said that constraints do more than just describe design intent to tools. "Constraints are as important as design data," he said. "We all have to realize that constraints are proprietary to the customer. They need to be open to all tools by all vendors."

In a discussion after the forum, Millman said that analog constraints could also apply to simulation, optimization and design-for-manufacturability.

"I think we all believe this should operate within OpenAccess, although it needs to be a textual representation that a human can sit down and read," Millman said.

Ferguson said that constraints are needed for parameterized-cell (p-cell) generation and automated custom placement and routing. He said constraints must be reliable and easy to use, and that information has to be compact. But, currently, he noted, each vendor is creating its own proprietary semantics, properties, data and formats, resulting in error-prone translations.

Analog layout vendor Silicon Canvas provides constraints through a rule-driven flow, said Morse. These might include rules for discrete gate spacing, minimum area and routing jog avoidance.

"Constraints from different vendors operate in the same basic ways, but with different methodologies and syntax," Morse said. "The time is now to create an open constraint format. If we allow it to be defined by a small group of vendors, we deserve what we get."

Cadence disagrees. "It's clear constraints have significant value, but it's still early in the technology for users to be thinking about standardization," said Gadient. First, he said, there needs to be some agreement on common design styles.

A formal standards effort isn't happening immediately. Lechner said the interoperable p-cell library group is first focusing on open p-cells, and is not likely to address analog constraints until after the Design Automation Conference next month. No decision has been made about where to take a standards effort, although the OpenAccess Coalition would be a "logical choice," he said.

From Si2's perspective, English said, the main question is whether an analog constraint format would influence the "core" of Open- Accessa step that would require involvement from OpenAccess creator Cadenceor whether it would be a simpler, "noncore" addition that could be handled with the application programming interface.

"We have a constraint subsystem that is extensible in nature, and this may just require new definitions of properties," English said. "It may just be a use-model question." The next step, he said, is for someone to request a technology enhancement that can go through the procedures established by the OpenAccess Coalition to set up a scheduled project.

- Richard Goering
EE Times

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