How do die, core, and core offset differ?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Last updated:
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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