For 7 series and UltraScale parts, a method similar to the placer estimation of congestion is used by way of the following metrics:
- Vertical routing congestion per CLB
- Horizontal routing congestion per CLB
Both of these metrics show a demand-based model that estimates the requirement for routing going between two points. When the demand exceeds 100, routing in adjacent tiles is used. Congestion is proportional to the area of the die where demand is consistently exceeding 100%.
Note: This method is still available for newer device families, but it is not recommended for use.