What is the correct order for fixing an early congestion hot spot?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Confirm data and constraints, locate demand and capacity, identify the physical cause, make the smallest causal change, then rerun the same measurement.
Technical Explanation
Do not enlarge the die before knowing whether the hot spot comes from pins, macros, PG, blockages, buses, or layer restrictions. Inspect direction and layer, pin walls, high-fanout nets, channel geometry, row density, and reserved resources together.
Formula Or Decision Rule
Decision rule: the fix must reduce the diagnosed demand or restore the missing capacity without moving the problem elsewhere.
What To Check
• Warning sign: Global area is increased but the same macro corner remains blocked. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Change the responsible macro, pins, channel, blockage, PG corridor, aspect ratio, or layer plan and compare before/after maps.
Command Checks & Actions
• report_congestion -mode hot_spot: reports routing demand, capacity, overflow, or hot spots
• create_channel_congestion_map -congestion_map_only true: estimates congestion in channel regions
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Confirm data and constraints, locate demand and capacity, identify the physical cause, make the smallest causal change, then rerun the same measurement. • Suspicious: Global area is increased but the same macro corner remains blocked. • Hard stop: required legality or physical feasibility is missing or unexplained. Change the responsible macro, pins, channel, blockage, PG corridor, aspect ratio, or layer plan and compare before/after maps.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. Global area is increased but the same macro corner remains blocked.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “What is the correct order for fixing an early congestion hot spot?” to measurable physical evidence and an owned correction.
Follow-up Question & Model Response
Follow-up probe: What would make you change your decision? Model response: “I would change it if the same controlled rerun shows that global area is increased but the same macro corner remains blocked. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: Global area is increased but the same macro corner remains blocked. Corrective path: Change the responsible macro, pins, channel, blockage, PG corridor, aspect ratio, or layer plan and compare before/after maps.
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