Why can the exact same physical path pass timing in one view and fail in another?
From PDVerse MMMC Interview Masterclass · pdVerse Mentor Series
Direct answer
Because "the same path" is only the same topology — it isn't the same electrical or timing condition. Change the mode, the corner, or both, and you change the active clocks, the cell delays, the wire delays, and possibly the check itself.
Mentor explanation
It's a natural instinct to think a path is either fast or slow, period. But a path's delay is assembled fresh in every view: which clock relationship applies (from the constraint mode), which library governs cell delay (from the library set), which parasitics govern wire delay (from the RC corner), and what slew and load conditions ripple through the whole chain. Two views can share the same netlist and the same physical route and still produce very different slack, because every ingredient feeding that slack number can independently change. The path is constant. Nothing else is.
Key takeaways
- Because "the same path" is only the same topology — it isn't the same electrical or timing condition.
- Change the mode, the corner, or both, and you change the active clocks, the cell delays, the wire delays, and possibly the check itself.
Self-check: can you answer this aloud?
Try a 45-second answer using this structure:
- State the direct answer.
- Explain the timing or physical reason.
- Name one caveat.
- Say how you would verify it in a real flow.
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