STA Mastery · All levels
Constraint Bug Patterns: Comparison Matrix
Comparison Matrix for Constraint Bug Patterns.
Comparison matrix
Debug order prevents expensive wrong-owner ECO.
+------------------+----------------+----------------+----------------+
| Approach | Strength | Weakness | Best when |
+------------------+----------------+----------------+----------------+
| Conservative | safe | slow closure | risk-averse |
| Balanced | practical | needs discipline | production |
| Aggressive | fast | regression risk | tapeout crunch |
| RTL change | structural | long loop | architectural |
+------------------+----------------+----------------+----------------+When to choose each approach
Match approach to schedule and silicon risk
Interview traps
One-size ECO playbook
Ignoring hold
Evidence comparison
STA EVIDENCE MATRIX — Constraint Bug Patterns
+-------------------+------------------------+--------------------------+-------------------------+
| Evidence | Tells you | Does not prove | Next action |
+-------------------+------------------------+--------------------------+-------------------------+
| report_timing | critical path slack | root cause class | cell vs net split |
| clock report | clock reachability | path delay | fix generated_clock |
| SDC diff | constraint change | physical delay | re-run all scenarios |
| SPEF tag compare | parasitic view | constraint quality | isolate view mismatch |
| MMMC dashboard | worst scenario | single-path fix | assign path group owner |
+-------------------+------------------------+--------------------------+-------------------------+STA deep dive
Debug hygiene separates senior STA leads from report readers.
Concept diagram
DEBUG ORDER
1. same tags? 2. constraints? 3. view? 4. real path? 5. ECOMetric graph
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
Most 'mystery' STA failures are wrong clocks, missing generated clocks, bad I/O delay, or over-broad exceptions.
Metric: false violation count after SDC fix, constraint audit pass rate