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STA Mastery · All levels

Path Group War Room: Interview Drills

Interview Drills for Path Group War Room.

Interview drills

Interview Drills for Path Group War Room focuses on WNS per path group, endpoint owner assignment rate. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

diagram
PROMPT
You see WNS per path group, endpoint owner assignment rate on Path Group War Room. Walk through root cause and fix.

STRONG ANSWER
1. Names corner/mode/view and path group.
2. Explains War rooms assign failing path groups to owning teams (RTL, synth, PD, CTS) based on delay breakdown and path class.
3. Requests path group heatmap, owner assignment sheet, daily WNS standup notes.
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

War room board

diagram
PATH GROUP | WNS  | OWNER    | ACTION
reg2reg    | -80  | PD       | upsize buf
in2reg     | -40  | STA+pkg  | IO delay review
reg2cg     | -25  | CTS      | skew check

Root-cause tree to narrate

diagram
ROOT-CAUSE TREE — Path Group War Room

WNS per path group, endpoint owner assignment rate 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

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DEBUG ORDER

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

Metric graph

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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

War rooms assign failing path groups to owning teams (RTL, synth, PD, CTS) based on delay breakdown and path class.

Metric: WNS per path group, endpoint owner assignment rate

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