Clock/Reset + DFT Interactions: Expanded Case Study

Extended case study

Tapeout readiness review flags scan mode timing escapes, test-mode bring-up issues in Clock/Reset + DFT Interactions.

Background

Local checks looked acceptable, but cross-domain integration evidence diverged on final merge baseline.

Symptoms observed

• scan mode timing escapes, test-mode bring-up issues regression

• Owner disagreement

• Conflicting artifacts

Investigation timeline

1. Hour 0: freeze baseline manifest and open risks

2. Hour 1: isolate failing boundary and first symptom

3. Hour 2: map symptom to owner contract

4. Hour 3: propose bounded reversible fix

5. Hour 4: execute focused re-run

6. Hour 5: run full regression matrix

7. Hour 6: document decision and residual risk

Root cause

Root cause tied to Clock/Reset + DFT Interactions: Functional and test clocks/resets share infrastructure; missing mode-specific constraints and mux assumptions often break ATPG or silicon bring-up.

Fix and validation

• Contract-aligned fix

• Re-run mode matrix, scan clock/reset constraints, DFT integration checklist

• Cross-domain owner signoff

Lessons learned

• Manifest before debate

• Fix owner boundary first

• Quantify residual risk

CASE STUDY — Clock/Reset + DFT Interactions
pre-fix risk / post-fix risk / regression confidence

Integration sequence under stress

SOC INTEGRATION FLOW — Clock/Reset + DFT Interactions

requirements + budgets
        |
        v
IP handoff + collateral check
        |
        v
integration build + bring-up smoke
        |
        v
cross-domain signoff evidence
        |
        v
tapeout readiness decision

Metric in focus: scan mode timing escapes, test-mode bring-up issues

SoC deep dive

Clock/reset assumptions must be globally consistent across functional and test modes.

Concept diagram

CLOCK/RESET FLOW
pll lock -> clock enable -> reset release -> domain ready

Metric graph

BOOT STABILITY
stable boots ████████
reset hangs  ███

Reports and artifacts

• clock architecture report

• reset release timing

• mode matrix

• boot trace summary

Mini case study

Intermittent boot hang traced to one domain releasing reset before dependent clock was stable.

Debug branches

• Check mode-specific constraints

• Trace reset dependencies

• Correlate firmware sequencing

Senior review question

Ask: what baseline, owner, and artifact prove this topic is truly closed?

Key takeaways

• State baseline manifest and owner with every closure metric.

• Run cross-domain regression after every top-level fix.

Common pitfalls

• Comparing results across different manifests.

• Unowned issues slipping through review cycles.

• Waiving risks without expiry and validation plan.

Principal SoC review addendum

Functional and test clocks/resets share infrastructure; missing mode-specific constraints and mux assumptions often break ATPG or silicon bring-up.

Metric: scan mode timing escapes, test-mode bring-up issues