A voltage-area boundary strands cells or creates an unusable sliver. How do you diagnose it?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Compare assigned cell area and growth with legal rows, guard bands, enclosure, boundary cells, switch/interface-cell zones, macro overlap, and supply access.
Technical Explanation
Enough polygon area can still contain too little usable placement area. Test region shape, target utilisation, row fragments, isolation and level-shifter locations, nested/overlap rules, and neighbouring domain demand.
Formula Or Decision Rule
Decision rule: use usable in-domain rows and interface access, not polygon area alone.
What To Check
• Warning sign: The region is enlarged in a direction that adds no usable rows. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Reshape or relocate it, rebuild affected rows and boundaries, and rerun multivoltage/floorplan checks.
Command Checks & Actions
• create_voltage_area -power_domains <domain_list> -region <region_list> -target_utilization <ratio> -name <voltage_area>: creates a physical region for one or more power domains
• report_design -floorplan: reports the floorplan state understood by the tool
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Compare assigned cell area and growth with legal rows, guard bands, enclosure, boundary cells, switch/interface-cell zones, macro overlap, and supply access. • Suspicious: The region is enlarged in a direction that adds no usable rows. • Hard stop: required legality or physical feasibility is missing or unexplained. Reshape or relocate it, rebuild affected rows and boundaries, and rerun multivoltage/floorplan checks.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The region is enlarged in a direction that adds no usable rows.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “A voltage-area boundary strands cells or creates an unusable sliver. How do you diagnose it?” 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 the region is enlarged in a direction that adds no usable rows. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: The region is enlarged in a direction that adds no usable rows. Corrective path: Reshape or relocate it, rebuild affected rows and boundaries, and rerun multivoltage/floorplan checks.
Continue practising