Why is report_ocvm -type pocvm -cell_delay -list_not_annotated an important pre-signoff check, and what does a missing cell imply?
From PDVerse PrimeTime STA Interview Guide · pdVerse Mentor Guide
Ten-second Interview Answer
It lists cells with no POCV coefficient or distance data, which fall back to zero variation. Any path through such a cell has under-modeled spread, so its corner is optimistic - a silent hole that can hide a real violation behind a normal-looking report.
Complete Technical Explanation
report_ocvm -type pocvm -cell_delay -list_not_annotated enumerates the cells that lack POCV coefficient or distance data - cells that neither LVF nor a side file annotated, and which therefore fall back to zero variation or to default behavior. A missing cell is a silent accuracy hole: it contributes no sigma to the statistical propagation, so every path through it has under-modeled variation and its corner value is optimistic, showing less spread than reality and potentially masking a real violation. What makes it dangerous is precisely that it fails quietly - the timing report looks entirely normal, just with distributions that are too tight, so nothing prompts you to look. The check does not need a timing update, so you can run it before update_timing and catch annotation gaps early, which is when they are cheap to fix. The usual causes are a library missing LVF tables for certain cells, a side-file object_spec that did not match the names you thought it would, or new cells introduced into the design after the POCV data was generated. The fix is to ensure every timing-relevant cell has POCV data, whether through complete LVF or through side-file coverage. Think of it as the POCV form of the general completeness discipline: the presence of variation data on every cell is what makes a statistical signoff trustworthy, and an un-annotated cell is a path carrying a hidden confidence gap that no slack number will ever reveal to you.
In Pd / Signoff
Run it as the first gate of POCV signoff, before the first update_timing, and require a zero-length list or a written explanation per entry. When it flags cells, the triage is library coverage first, then side-file object_spec matching, then a check for cells added by recent ECOs. Archive the empty list as signoff evidence.
Common Trap
Skipping the check because the timing reports look fine. They will look fine - an un-annotated cell removes sigma rather than adding an error message, so the slack is optimistically tight and nothing in a normal report distinguishes it from a genuinely clean path.
Expect Next
If the not-annotated list names only a handful of non-critical cells, how would you decide whether to waive them?
Topic And Primetime Commands
Variation / AOCV Tables. report_ocvm, update_timing
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