How do you verify macro and block-grid alignment?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Check macro origin, boundary, orientation, alignment point, and applicable block or FinFET grid. Movement, rotation, mirroring, and snapping are separate operations.
Technical Explanation
A macro can be inside the core yet land on an illegal manufacturing or block-grid coordinate. Multiply instantiated blocks and advanced-node macros may have stricter alignment relationships than ordinary standard cells.
Formula Or Decision Rule
Decision rule: all required coordinates and dimensions satisfy the owning grid after final orientation.
What To Check
• Warning sign: A legal orientation becomes off-grid after a manual move. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Snap to the approved grid, recheck boundary clearance and pins, and record the final coordinates.
Command Checks & Actions
• set_macro_constraints -alignment_grid <grid_name> -alignment_point <align_point> <macro_collection>: records allowed macro or I/O placement constraints
• check_design -checks {dp_pre_macro_placement}: runs named design-planning check groups
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Check macro origin, boundary, orientation, alignment point, and applicable block or FinFET grid. Movement, rotation, mirroring, and snapping are separate operations. • Suspicious: A legal orientation becomes off-grid after a manual move. • Hard stop: required legality or physical feasibility is missing or unexplained. Snap to the approved grid, recheck boundary clearance and pins, and record the final coordinates.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A legal orientation becomes off-grid after a manual move.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do you verify macro and block-grid alignment?” 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 legal orientation becomes off-grid after a manual move. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: A legal orientation becomes off-grid after a manual move. Corrective path: Snap to the approved grid, recheck boundary clearance and pins, and record the final coordinates.
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