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What is WNS (Worst Negative Slack)?

From PDVerse STA Mentor Guide · pdVerse Mentor Guide

Short Answer

WNS, or Worst Negative Slack, is simply the single most negative slack value found anywhere in the design among all the violating (failing) paths.

Example

Given five violating slacks in picoseconds of -12, -8, -5, -3, -2, the WNS is -12, since that is the most negative (worst) value in the group.

Why It Matters

WNS tells you how bad your single worst timing problem is. It's a quick headline number for judging the severity of the worst offender, even though it says nothing about how many other paths are also failing.

Mentor Note — Common Mistake

Don't confuse WNS with how widespread the problem is. A single very bad path could dominate WNS while nearly all other paths are fine; for that you need TNS instead.

Visual explanationSTA context: What is WNS (Worst Negative Slack)?
STA context: What is WNS (Worst Negative Slack)?A three-step concept map summarizes the focus, core answer, and practical verification for What is WNS (Worst Negative Slack)?Question focusWhat is WNS (WorstNegative Slack)?Core answerWNS, or Worst NegativeSlack, is simply thesingle most negativeslack…Verify in practiceConfirm the path,constraints, clockassumptions, and timingreport.Understand → explain the mechanism → verify the assumptions

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