What is the difference between a legal pin and an accessible pin?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
A legal pin obeys placement rules; an accessible pin also has a usable routing approach on an allowed layer and track without blockage or spacing conflict.
Technical Explanation
A door can be drawn on a wall yet be impossible to reach because furniture blocks it. Check track alignment, layer direction, corner crowding, stacked shapes, routing blockages, PG shapes, and detour needs.
Formula Or Decision Rule
Decision rule: a boundary touch is insufficient; require at least one legal routing approach consistent with the route plan.
What To Check
• Warning sign: Pins pass geometry checks but all nearby tracks are blocked or reserved. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Move, spread, re-layer, or regroup pins and then rerun targeted pin and congestion checks.
Command Checks & Actions
• check_pin_placement: checks pin-placement legality and access-related conditions
• report_pin_placement -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: A legal pin obeys placement rules; an accessible pin also has a usable routing approach on an allowed layer and track without blockage or spacing conflict. • Suspicious: Pins pass geometry checks but all nearby tracks are blocked or reserved. • Hard stop: required legality or physical feasibility is missing or unexplained. Move, spread, re-layer, or regroup pins and then rerun targeted pin and congestion checks.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. Pins pass geometry checks but all nearby tracks are blocked or reserved.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “What is the difference between a legal pin and an accessible pin?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: Pins pass geometry checks but all nearby tracks are blocked or reserved. Corrective path: Move, spread, re-layer, or regroup pins and then rerun targeted pin and congestion checks.
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