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40 DESIGN007 MAGAZINE I MAY 2019 Wiens: Right. And in the old "Wild West" of de- sign, there wasn't a con- straint editor. Then, you got constraints and had an engineer talking over your shoulder, saying, "When you route these two trac- es, keep them this far apart." It was all digitized, and you had to use old-fashioned ways to de- termine whether they were far enough apart. There was no such thing as a digital constraint or something to adhere to. The idea of becoming aware of all of them is a big thing, so from an EDA perspective, we try to automate these things. We help gather all of those constraints in one place. There are still things that can be done to improve on that. It's about having a streamlined way so that you can pass constraints from whoever defined them. If it came from the engineer at the front or the manufacturing NPI engineer at the back, the process helps define those and pass them to the person who has to implement them. Shaughnessy: Many designers say they don't even know who is going to be fabricating their board or prototype, much less production. How do you figure all of that in the design rules? Do you have to re-enter it each time? Wiens: In most tools you do. Not just every job, but you want to be able to design for multi- ple manufacturers, for instance. And you defi- nitely want to be able to retarget, and that's one of the things that we've been able to do thanks to our Valor technology. The majority of manufacturers out there, around 80%, use Valor for their verification tool. If they're us- ing Valor, they can pass the designer those rule decks. Then, the designer can retarget without having to reenter a bunch of constraints. They can say, "I want to go after this manufacturer instead of this one," and do it with a rule deck that the majority of manufacturers use. To bring up a common theme, last fall, we talked to you regarding the "shift left," bring- ing verification earlier into the design process. That plays into this as well. Again, it's about constraint definition, adherence, and verifica- tion, trying to bring the full board verification early on in the process so that it's not just used as a sign off tool at the end. Instead, it should be used throughout to help ensure that the de- signer becomes smarter and more aware of en- gineering and manufacturing and produces a product that can meet the constraints. For instance, in manufacturing, there are tol- erances. If you do this, it will work, but if you do this, it will be lower cost and still work. So, what are the absolute rules, and what are the gray-area rules? You have to deal with some level of tolerance; over-constraining a design is easy, and to some degree, lazy. If you talk to your average layout designers, they'll go off on this. They'll say that the engineer gave them a constraint, and there's no way to meet it. De- fining hardline constraints is easy but defining constraints that work with other constraints and the tradeoffs that can be implemented within tolerances is a lot harder. Shaughnessy: Meanwhile, you're pushing the envelope with the technology, and I'm sure that makes it more difficult with each revision of the tool that comes out. Wiens: With increasing design complexity comes additional constraints. And there are all kinds of constraints that have to be thought of to fire a 28-Gb signal across a board. We have to continually increase the constraints that somebody can set for that; at the same time, we need to try to make it as simple as possible to do that. Defining constraints can be somewhat onerous. Great, you have an en- vironment to define those constraints, but do I have to be a Ph.D. to do it? Shaughnessy: Theoretically, there's almost no limit to the number of design rules you can have for a design. Wiens: Right. Your average board has tens of thousands of connections and nets. You could constrain each one of them independently if you wanted to, but that's where reality has to Dave Wiens

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