A block pin is legal but off-track, stacked, or on an unusable layer. What is the response?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Treat this as a pin-access defect. Report the pin geometry and nearby tracks/resources, then move, spread, reorder, or re-layer it within the interface constraints.
Technical Explanation
Legality proves rule compliance, not route entry. Hypotheses include wrong offset, blocked nominal track, layer mismatch, corner crowding, PG conflict, or bundle ordering. Targeted checks separate them.
Formula Or Decision Rule
Decision rule: require a legal approach on an allowed, unblocked routing resource.
What To Check
• Warning sign: The pin is snapped to the nearest nominal track without checking usability. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Correct the actual cause and rerun pin placement plus local congestion.
Command Checks & Actions
• check_pin_placement -alignment true -layer_mismatch_only true -blocked_only true: checks pin-placement legality and access-related conditions
• report_pin_placement -pins <pins> -format {layer side offset}: reports pin layer, side, and offset
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Treat this as a pin-access defect. Report the pin geometry and nearby tracks/resources, then move, spread, reorder, or re-layer it within the interface constraints. • Suspicious: The pin is snapped to the nearest nominal track without checking usability. • Hard stop: required legality or physical feasibility is missing or unexplained. Correct the actual cause and rerun pin placement plus local congestion.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. The pin is snapped to the nearest nominal track without checking usability.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “A block pin is legal but off-track, stacked, or on an unusable layer. What is the response?” 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 pin is snapped to the nearest nominal track without checking usability. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: The pin is snapped to the nearest nominal track without checking usability. Corrective path: Correct the actual cause and rerun pin placement plus local congestion.
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