Pin constraints conflict with routing blockages or PG shapes. Who owns the fix?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
The uncomfortable reality of this conflict is that both constraints can be individually valid and still be jointly impossible to satisfy at the same location — this isn't a case of one side simply being wrong. Ownership resolution starts by figuring out which constraint is actually authoritative here: package/interface intent, the block pin constraint itself, the routing blockage, or the PG reservation — and that's a negotiation between whoever owns each of those, not a unilateral PD call.
Technical Explanation
- Use the pin checks (exact reported layer/side/offset), the local blockage geometry, and the planned PG corridor layout together to see precisely where and how they collide.
- The resolution needs to preserve required function explicitly — if the pin carries a differential signal, a clock, or a supply connection, that functional requirement constrains what geometry changes are even acceptable, so keep those needs stated up front in the negotiation.
- This connects to the "return to owner" pattern elsewhere in this set — recognizing that a conflict needs cross-team negotiation rather than a silent local override is itself the correct PD judgment call.
Formula Or Decision Rule
Decision rule: the final pin has legal access and the blockage/PG purpose remains satisfied.
What To Check
- Warning sign: One team deletes the other team’s constraint locally.
- Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
- Correct: Return evidence to the interface, floorplan, or power owner, agree on the change, and rerun both checks.
Command Checks & Actions
- check_pin_placement -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
report_congestion-mode hot_spot: reports routing demand, capacity, overflow, or hot spots
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.
Healthy, Suspicious & Hard-stop Results
- Healthy: Identify whether package/interface intent, block pin constraints, routing blockage, or PG reservation is authoritative, then negotiate a geometry that preserves the required function.
- Hard stop: required legality or physical feasibility is missing or unexplained.
Common Mistake
The Trap: Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “Pin constraints conflict with routing blockages or PG shapes. ” to measurable physical evidence and an owned correction.
Follow-up Question & Model Response
"* Candidate Model Response: Model response: “I would change it if the same controlled rerun shows that one team deletes the other team’s constraint locally. ”
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