原创 Timing constraint more problematic than it seems

A recent survey conducted by EDA vendor Atrenta Inc. concludes that timing constraints can result to more than a few headaches and some lost hours of sleep.

Less than 10 percent of respondents to the survey said that timing constraints rarely presented a problem in the design flow. More than 10 percent said timing constraints created a problem every day, 29 percent said they created problems a few times in a typical project and nearly 52 percent said they created problems frequently in a typical project.

More troubling, 29 percent of respondents said that in cases were timing constraints presented a problem the consequences included silicon failure. Nearly 59 percent said consequences included tape out delay. In all, nearly 85 percent of respondents said timing constraints issues resulted in difficulties meeting timing.

What are designers doing in the face of such a vexing issue that could potentially cause their chip to fail? Most—nearly 73 percent—responded that they implemented stricter guidelines for timing constraint development. Nearly 14 percent of respondents said they had made no changes to their design flow or process to combat timing constraint issues.

"In effect, 73 percent of respondents said, 'We'll just try harder,' " said Ron Craig, senior marketing manager at Atrenta. "Too many heads are still stuck in the proverbial sand. People don't fully recognize the magnitude of the problem."

Half of the respondents said they verify timing constraints manually. Sixty-eight percent said they rely on synthesis and timing tools to point out the mistakes. (Obviously, respondents were allowed to give more than one answer to the question.

But according to Craig, synthesis and timing tools are not really designed to catch bad constraints. They end up missing a lot of things, such as overlapping constraints, he said. Manual verification has become too difficult as designs have grown exponentially, he added.

"The solution is to be more proactive," Craig said. "You can have 95 percent good constraints before you even start using them. If you know up front that things are good then you avoid all of these issues and things sneaking through."

You knew this was coming. Surprise: Atrenta sells a tool, SpyGlass Constraints, which automates the creation, validation and management of constraints. The survey—a survey of Atrenta customers which 66 people responded too—found that only about 26 percent of respondents were using SpyGlass Constraints. Eighteen percent of respondents said they were using another third-party tool to verify and manage timing constraints.

Obviously, Craig believes more designers to need to adopt third-party tools to manage constraints. And it's a safe bet he prefers that they use SpyGlass Constraints. But he acknowledged that it can be a tough sell to get customers to pony up to add a new tool to their flow. A certain part of that, he said, is human nature—designers feel that if they overcome the timing constraints difficulties with their last chip they can do it again with their next without spending money for a new tool.

Craig's message to designers: "Your experience and your productivity isn't keeping up with the complexity of your constraints and the number of issues you are taking on."

Dylan McGrath

EE Times