15.7.5.2 Use Empty Regions to Reduce Routing Congestion

Creating empty regions next to the congested area(s) of your design helps reduce congestion. When you place an empty region next to congested logic blocks or regions, the placer cannot place any logic next to your region or logic block.

Logic, which would normally be placed there, is forced to be placed somewhere else. Routing resources next to the congested area are, therefore, freed up and provide the router more options to route signals into the congested block.

Before deciding to place empty region(s), analyze your design for congestion areas. Use the Ratsnest view in ChipPlanner to see dense areas of connectivity into and out of your logic blocks or regions. Create empty regions in these congested areas and see it if improves the routability of your logic.