What is TNS (Total Negative Slack)?
From PDVerse STA Mentor Guide · pdVerse Mentor Guide
Short Answer
TNS, or Total Negative Slack, is the sum of all the negative slack values across every violating path in the design, not just the worst one.
Example
For the same five violating slacks in picoseconds, -12, -8, -5, -3, -2, adding them together gives a TNS of -30, with a violation count of 5.
Why It Matters
TNS gives you a sense of the overall scope of the timing problem across the whole chip, since it accounts for every failing path, not just the single worst case. A design could have a mild WNS but a huge TNS if many paths are failing by a little bit each, or a severe WNS with a small TNS if only one path is really bad.
Mentor Note — Common Mistake
Don't rely on WNS alone to judge overall design health. Two designs can have the same WNS but very different TNS values, and TNS is what reveals whether the failures are isolated or widespread.
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