What do MPH and MPL checks actually verify, and where else does MPL-style logic show up?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
MPH (Minimum Pulse Width High) verifies a clock's positive pulse stays high long enough; MPL (Minimum Pulse Width Low) verifies the negative pulse stays low long enough. The same underlying MPL-style logic is also used for transparent-latch setup/hold slack adjustments -- a latch's transparent window has to stay open long enough for data to actually pass through it, which is structurally the same "minimum duration" problem as a clock pulse.
Technical Explanation
- MPH (Minimum Pulse Width High) verifies a clock's positive pulse stays high for at least the required duration.
- MPL (Minimum Pulse Width Low) verifies the negative pulse stays low for at least the required duration.
- The same MPL-style logic is reused for transparent-latch setup/hold slack adjustments -- a latch needs its transparent window open long enough for data to pass through, structurally the same minimum-duration problem as a clock pulse width check.
report_timing -check_type min_pulse_widthis the direct command for observing MPH/MPL violations at a clock pin, rather than inferring them from the constraint definition alone.
Common Mistake
The Trap: Treating MPH/MPL as purely a clock-tree DRC concern with no connection to latch-based timing -- the same underlying logic governs both.
Follow-up Question & Model Response
"Why would a latch's transparent window and a clock's pulse width share the same underlying check logic?"
Candidate Model Response: Both are fundamentally asking the same question: is this signal held at a given state for at least a minimum required duration? A clock pulse and a latch's transparent window are both bounded time intervals that need a minimum width to do their job correctly.
Practical Example
Tapeout Scenario: A clock tree with excessive duty-cycle distortion from unequal rise/fall buffer delays shows an MPL violation on the negative pulse -- the same class of check that, on a latch-based design, would also flag an undersized transparent window.
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