How to Analyze and Fix Post-Placement Congestion?

o   Congestion Maps: Use the PnR tool's GUI to visualize the congestion map generated after trial/global routing. Identify hotspots (high overflow areas, usually color-coded red/orange). Check both horizontal and vertical layer congestion.

o   reportCongestion - list the most congested regions.

Reasons could be - High Cell Density -  Macro Pin Areas - Narrow Channels  - Bad Floorplan - Specific Logic: Are certain types of logic (e.g., large muxes, data path logic) concentrating connections in one area?

o   Fixing/Preventing Congestion:

o   Update Floorplan

o    Placement Blockages (Partial):

o    Maximum Utilization/Density Constraints

o    Cell Spreading/Padding:

§  Cell Padding:

o   Optimize Placement Settings:

o   Congestion-Driven Effort: setPlaceMode –congEffort high). The tool will prioritize reducing congestion, potentially at the expense of timing/wirelength initially.

o   Guidance (Bounds/Regions): Use placement bounds (guides, regions)

o    Congestion Analysis/Fixing: https://vlsiweb.com/congestion-analysis/