STA Mastery · All levels

View Mismatch Triage: Interview Drills

Interview Drills for View Mismatch Triage.

Interview drills

Interview Drills for View Mismatch Triage focuses on slack delta between views, SPEF tag mismatch count. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

diagram

PROMPT
You see slack delta between views, SPEF tag mismatch count on View Mismatch Triage. Walk through root cause and fix.

STRONG ANSWER
1. Names corner/mode/view and path group.
2. Explains Different SPEF, RC corners, or parasitic modes between runs explain apparent regressions without any design change.
3. Requests view diff report, SPEF metadata, run comparison script.
4. Proposes one reduced sequence and one system regression.

WEAK ANSWER
Jumps to upsizing cells, widening routes, or blaming tools without reading constraints and path delay.

Diagram to draw on the whiteboard

Run diff checklist

diagram

COMPARE TWO STA RUNS
same?  netlist tag
same?  SDC tag
same?  SPEF tag / corner
same?  lib corner map
same?  tool version
first NO -> explain slack delta

Root-cause tree to narrate

diagram

ROOT-CAUSE TREE — View Mismatch Triage

slack delta between views, SPEF tag mismatch count looks wrong
        |
   same netlist tag?
     /        \
   no          yes
   |            |
 view/SDC     real path or
 mismatch     constraint bug
 /    \           |
lib   SPEF    delay breakdown
diff  diff    cell vs net

STA deep dive

Debug hygiene separates senior STA leads from report readers.

Concept diagram

diagram

DEBUG ORDER

1. same tags?  2. constraints?  3. view?  4. real path?  5. ECO

Metric graph

diagram

ROOT CAUSE MIX (typical)

constraint bugs  ████████  35%
view mismatch    ██████    25%
real path        ██████    25%
methodology      ████      15%

Reports and artifacts

run manifest
SDC diff
SPEF tag
scenario isolation

Mini case study

Mystery regression: SPEF corner tag typo in run script — not a design bug.

Debug branches

Manifest every run
War room by path group

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

Key takeaways

State corner, mode, view, and database tag with every slack claim.
Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

Comparing STA runs with different SPEF or SDC tags.
Broad false_path to green-wash violations.
Setup-only ECO without hold check.

Principal STA review addendum

Different SPEF, RC corners, or parasitic modes between runs explain apparent regressions without any design change.

Metric: slack delta between views, SPEF tag mismatch count

Practice this lesson