How should hierarchical block pins be placed?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Place block pins on legal sides, layers, tracks, and offsets according to top-level dataflow, routing corridors, bundles, and feedthrough intent.
Technical Explanation
A block pin is a doorway shared with the parent design; both sides need usable access. Use pin constraints and guides, exclude inappropriate nets, place or legalise targeted collections, then report exact layer/side/offset.
Formula Or Decision Rule
Decision rule: a pin location must work for both internal and external routing.
What To Check
• Warning sign: Pins are evenly spaced but force top-level detours or internal crossovers. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Regroup, reorder, re-layer, or move the pins and rerun pin/access and congestion checks.
Command Checks & Actions
• place_pins -cells <cells> -pins <pins> -legalize: places or legalises targeted pins
• 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: Place block pins on legal sides, layers, tracks, and offsets according to top-level dataflow, routing corridors, bundles, and feedthrough intent. • Suspicious: Pins are evenly spaced but force top-level detours or internal crossovers. • Hard stop: required legality or physical feasibility is missing or unexplained. Regroup, reorder, re-layer, or move the pins and rerun pin/access and congestion checks.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. Pins are evenly spaced but force top-level detours or internal crossovers.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How should hierarchical block pins be placed?” 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 pins are evenly spaced but force top-level detours or internal crossovers. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: Pins are evenly spaced but force top-level detours or internal crossovers. Corrective path: Regroup, reorder, re-layer, or move the pins and rerun pin/access and congestion checks.
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