What does -check_prerequisites on place_group_repeaters actually validate before attempting placement, and what do a couple of its real error codes tell you?

Short Answer

-check_prerequisites validates a real checklist before placement is attempted: site rows present, each net has one driver and can have multiple loads, pin/port locations assigned, standard cells carrying the pins are placed, supernets routed, route ends within 5 microns of driver/load pins in the search region, and more. Real error examples: ECO-329 ("the net net_wo_load does not have loads") and ECO-331 ("the cell driver1 of the pin driver1/X is not placed") -- both point to a genuinely missing prerequisite, not a placement algorithm failure.

Technical Explanation

• -check_prerequisites validates a real checklist BEFORE placement is attempted: site rows present, each net has exactly one driver (multiple loads allowed), pin/port locations assigned, standard cells carrying the pins are actually placed, supernets are routed, route ends are within 5 microns of driver/load pins/ports in the search region, and several more conditions.
• ECO-329 ("the net net_wo_load does not have loads") means exactly what it says -- the net has no loads at all, a structural netlist problem, not a placement algorithm issue.
• ECO-331 ("the cell driver1 of the pin driver1/X is not placed") means the driving cell for that pin hasn't been placed yet -- group repeater placement genuinely cannot proceed until the driver itself has a real location.
• Running -check_prerequisites BEFORE attempting the real placement catches these structural problems up front, rather than letting the actual placement operation fail partway through with a less clear error.

What To Check

• Warning sign: place_group_repeaters or add_group_repeaters fails with an ECO-3xx-series error mid-operation.
• Inspect: re-run with -check_prerequisites first to get a clear, structural diagnosis rather than debugging from the mid-operation failure alone.
• Correct: fix the specific structural issue -check_prerequisites identifies (missing loads, unplaced driver, etc.) before re-attempting placement.

Healthy, Suspicious & Hard-stop Results

• Expected: -check_prerequisites passes cleanly before real group repeater placement is attempted, or any reported issues are resolved first.
• Investigate: a group repeater placement operation fails mid-run with an ECO-3xx error -- re-run with -check_prerequisites to get a clearer, earlier diagnosis of the same underlying issue.
• Stop: group repeater placement is repeatedly re-attempted after failures without ever running -check_prerequisites to identify the actual structural cause.

What The Interviewer Is Testing

Whether you know -check_prerequisites is a real, substantive validation (not a formality) and can interpret specific documented error codes correctly, connecting them to real structural causes.