How do hard, soft, partial, and macro-only placement blockages differ?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
A hard blockage excludes placement, a soft blockage can permit selected later optimisation use, a partial blockage limits occupancy, and a macro-only restriction targets hard macros. Exact behaviour must follow the installed release and methodology.
Technical Explanation
A blockage is fixed geography, so choose it by the population you need to control. Partial blockage needs a declared blocked percentage. Routing blockages are separate because they constrain routing resources rather than cell placement.
Formula Or Decision Rule
Decision rule: name the object population and stage before choosing a blockage type.
What To Check
• Warning sign: A hard blockage is used to cure congestion without proving which population causes it. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Use the narrowest justified blockage, rerun placement/congestion estimates, and check displaced demand.
Command Checks & Actions
• create_placement_blockage -boundary {{<llx> <lly>} {<urx> <ury>}} -type partial -blocked_percentage <percentage> -name <blockage>: creates a fixed placement restriction
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 hard blockage excludes placement, a soft blockage can permit selected later optimisation use, a partial blockage limits occupancy, and a macro-only restriction targets hard macros. Exact behaviour must follow the installed release and methodology. • Suspicious: A hard blockage is used to cure congestion without proving which population causes it. • Hard stop: required legality or physical feasibility is missing or unexplained. Use the narrowest justified blockage, rerun placement/congestion estimates, and check displaced demand.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A hard blockage is used to cure congestion without proving which population causes it.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “How do hard, soft, partial, and macro-only placement blockages differ?” 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 hard blockage is used to cure congestion without proving which population causes it. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: A hard blockage is used to cure congestion without proving which population causes it. Corrective path: Use the narrowest justified blockage, rerun placement/congestion estimates, and check displaced demand.
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