How do die, core, and core offset differ?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
Picture the die as the full piece of land you own, and the core as the buildable footprint inside it — the core is where your standard-cell rows and most of your implementation actually lives. The core offset is simply the gap between the die edge and the core edge on each side — and crucially, that gap doesn't have to be the same on all four sides.
Technical Explanation
- Those offsets exist for real reasons: I/O pad structures, power rings, seal-ring clearance, or just physical access space for bonding/probing — they're reserved space, not wasted space.
- A common beginner mistake is assuming offsets are symmetric by default; always check the actual left/right/top/bottom values rather than assuming one number applies everywhere.
- g. left/bottom/right/top vs. some other order) varies, and getting it backwards silently produces a legal but wrong floorplan.
Visual Verification
The core area contains placeable standard cells and macros, separated from the outer die boundary by I/O pad rings, seal rings, power rings, and ESD protection margins.
Formula Or Decision Rule
Die width = left offset + core width + right offset; die height = bottom offset + core height + top offset.
What To Check
- Warning sign: The core touches an unintended die side or leaves too little room for required structures.
- Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
- Correct: Correct the boundary or offsets from package and power-planning requirements, then regenerate and report the floorplan.
Command Checks & Actions
initialize_floorplan-control_type core -core_offset {<side_1> <side_2> <side_3> <side_4>}: creates the initial die, core, rows or site array, and tracks from declared controlsreport_design-floorplan: reports the floorplan state understood by the tool
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.
Healthy, Suspicious & Hard-stop Results
- Healthy: The die is the outer design boundary; the core is the region used for standard-cell rows and most implementation objects. Core offsets are the distances from die sides to core sides.
- Hard stop: required legality or physical feasibility is missing or unexplained.
Common Mistake
The Trap: Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change.
What The Interviewer Is Testing
” to measurable physical evidence and an owned correction.
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