44 DESIGN007 MAGAZINE I MAY 2019
Shaughnessy: If you're a designer and use de-
sign rules all the time, do you have to go back
to validate them after each couple of projects?
Wiens: Yes. What was that rule based on? Was
it based on a manufacturing process? Does that
manufacturing process still exist? Is it still the
same cost? Are there alternatives? Was it based
on a certain performance in terms of the data
rate, DDR4 versus DDR5? What was that based
on? So, yes, that comes into play when you
think about whether or not you can reuse it.
Again, it's a moving target.
Shaughnessy: Is there anything that you would
recommend to one of your designer users or
anything that you wish that they would un-
derstand regarding setting up and using design
rules?
Wiens: If they know what their tool is capable
of, then they're more likely to leverage that,
and be more productive. One of the problems
with having a tool with a lot of horsepower
like Xpedition is that customers don't always
know what's under the covers, and constraint
management is a big area of that.
Shaughnessy: The more I find out about de-
sign rules, the more I'm surprised that we get
it right so often. There are so many potential
screw-ups.
Wiens: There's a margin for error, and that's a
good thing. Unfortunately, that margin usual-
ly comes at a cost. Everybody thinks, "At the
end of the day, I'll manufacture it, boot it up,
and if it works, I'm successful." But they might
have had to do it with a higher-cost manufac-
turing process, components, or complex stack-
ups. What does success look like, and what's
the best practice?
Shaughnessy: I know some designers over-con-
strain just to be thorough, and it costs more to
manufacture.
Wiens: Exactly. If that is baked into the pro-
cess, meaning everybody knows that it cost
this much to manufacture the last one, and no-
body raised an eyebrow when they did that,
I'm going to do it again. Designers and engi-
neers are incredibly smart people; it's not like
they're incapable of multidomain awareness,
but there are a lot of moving pieces. So, you
try to control as many of them as possible to
minimize the tradeoffs and options to be con-
sidered.
Shaughnessy: I appreciate you both taking the
time out to talk with me.
Wiens: Thanks for the opportunity.
Santarini: It's always good talking with you.
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