What three settings together actually determine whether pin-cost-aware, pin-density-aware, both, or neither placement behavior is active?

Short Answer

set_technology -node {7|7+|5|s5|s4} sets the tech-specific pin-cost model -- a prerequisite. place.coarse.pin_cost_aware (default false) and place.coarse.pin_density_aware (default false, applicable to all tech nodes) are two independent toggles. The COMBINATION of all three -- which node was set, and which of the two booleans are true -- determines the actual resulting behavior: pin-cost-aware placement, pin-density-aware placement, both, or neither.

Technical Explanation

• set_technology -node {7|7+|5|s5|s4} sets the tech-specific pin-cost model -- this is a PREREQUISITE for pin-cost-aware behavior specifically, tied to particular advanced node values.
• place.coarse.pin_cost_aware (default false) is one independent toggle.
• place.coarse.pin_density_aware (default false) is a SEPARATE independent toggle, and unlike pin_cost_aware, it's applicable to ALL technology nodes, not just the advanced ones set_technology -node lists.
• The actual resulting behavior depends on the COMBINATION of all three settings -- the node value plus both booleans -- not any single one in isolation. You can have pin-density-aware placement without pin-cost-aware placement (since density-aware doesn't need the specific node prerequisite), but pin-cost-aware placement specifically requires both its own boolean AND a matching -node setting.

What To Check

• Warning sign: pin_cost_aware is set true but no pin-cost-aware placement behavior is observed.
• Inspect: confirm set_technology -node was actually set to one of the specific supported values ({7|7+|5|s5|s4}) -- without it, the pin-cost model prerequisite isn't met regardless of the boolean.
• Correct: set both the matching -node value and pin_cost_aware=true together; they're both required, neither alone is sufficient.

Healthy, Suspicious & Hard-stop Results

• Expected: pin-cost-aware placement behavior is observed specifically when both set_technology -node (a supported value) and pin_cost_aware=true are set together.
• Investigate: pin_cost_aware is enabled but no corresponding behavior change is observed -- check whether set_technology -node was set to a supported value, since the boolean alone isn't sufficient.
• Stop: a design attempts pin-cost-aware placement on a technology node not in the supported set ({7|7+|5|s5|s4}) -- that combination cannot produce the intended behavior regardless of the boolean setting.

What The Interviewer Is Testing

Whether you know these are three genuinely independent settings whose COMBINATION determines behavior, and specifically that pin_cost_aware (unlike pin_density_aware) has a real node prerequisite.