A macro array is legal, but its allowed orientations create pin-access failure. How do you respond?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Do not force an illegal orientation. Test legal orientations, spacing, staggering, array order, pin-facing strategy, and surrounding routing layers; then change the array geometry if access remains impossible.
Technical Explanation
Legality restricts the solution space; it does not guarantee a routable member of that space. Check compiler symmetry, macro constraints, facing pin density, corner access, PG pins, block grid, and congestion for each allowed option.
Formula Or Decision Rule
Decision rule: the array proceeds only when an allowed orientation set has credible access.
What To Check
• Warning sign: A mirrored orientation is used even though the library disallows it. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Rework array order, spacing, or location and rerun macro and pin checks.
Command Checks & Actions
• set_macro_constraints -allowed_orientations <orientation_list> <macro_collection>: records allowed macro or I/O placement constraints
• check_design -checks {dp_pre_macro_placement}: runs named design-planning check groups
• check_pin_placement: checks pin-placement legality and access-related conditions
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Do not force an illegal orientation. Test legal orientations, spacing, staggering, array order, pin-facing strategy, and surrounding routing layers; then change the array geometry if access remains impossible. • Suspicious: A mirrored orientation is used even though the library disallows it. • Hard stop: required legality or physical feasibility is missing or unexplained. Rework array order, spacing, or location and rerun macro and pin checks.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A mirrored orientation is used even though the library disallows it.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “A macro array is legal, but its allowed orientations create pin-access failure. How do you respond?” 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 a mirrored orientation is used even though the library disallows it. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: A mirrored orientation is used even though the library disallows it. Corrective path: Rework array order, spacing, or location and rerun macro and pin checks.
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