One macro has a huge halo; another has pin-access failure from a small halo. How do you size them?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Use asymmetric, evidence-based margins where supported: reserve space where pins, vias, routing, or optimisation cells need it, and avoid wasting quiet sides.
Technical Explanation
A single uniform number ignores pin-side asymmetry. Compare macro-edge congestion, pin distribution, row fragments, PG shapes, and placed-cell demand on each side. Separate placement keepout from routing blockage needs.
Formula Or Decision Rule
Decision rule: each side’s margin protects a named resource without creating unusable area.
What To Check
• Warning sign: The same halo is copied to every macro. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Resize by side and type, then compare access, rows, and congestion.
Command Checks & Actions
• create_keepout_margin -type hard -outer {<left> <bottom> <right> <top>} <macro_collection>: attaches a typed keepout margin to design objects
• 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: Use asymmetric, evidence-based margins where supported: reserve space where pins, vias, routing, or optimisation cells need it, and avoid wasting quiet sides. • Suspicious: The same halo is copied to every macro. • Hard stop: required legality or physical feasibility is missing or unexplained. Resize by side and type, then compare access, rows, and congestion.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The same halo is copied to every macro.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “One macro has a huge halo; another has pin-access failure from a small halo. How do you size them?” 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 same halo is copied to every macro. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: The same halo is copied to every macro. Corrective path: Resize by side and type, then compare access, rows, and congestion.
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