How do you debug an off-track or blocked pin?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
A pin sitting right at the edge of a cell or macro can still have zero legal, track-centered way to approach it — "on the boundary" and "reachable" are different claims. Debugging means pulling the pin's exact layer, side, and offset and comparing that against the track pattern (pitch/offset/direction), any blockages nearby, PG shapes in the area, spacing rules, and neighboring pins that might be crowding the same tracks.
Technical Explanation
- Use the release's targeted alignment and blocked-pin checks rather than trying to eyeball track alignment — off-by-a-fraction-of-a-pitch errors are invisible at normal zoom.
- Once the automated check flags a pin, go inspect the actual pin shape geometry directly, not just the reported coordinate — sometimes the shape itself is malformed or too small to land a via on legally.
- This is the same class of problem as the notches/channels question — a pin can look fine and still be functionally unreachable once you account for every real constraint around it.
Formula Or Decision Rule
Decision rule: at least one allowed approach must remain after all reservations and spacing rules.
What To Check
- Warning sign: A pin is moved onto a nominal track that is reserved or blocked.
- Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
- Correct: Choose a usable track/layer or move the blockage and rerun the same targeted check.
Command Checks & Actions
- check_pin_placement -alignment 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: Report its layer, side, and offset; compare with the track pattern, preferred direction, blockages, PG shapes, spacing rules, and neighbouring pins.
- 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
” 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 a pin is moved onto a nominal track that is reserved or blocked. ”
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