Grouping critical logic to avoid crossing SLRs can help improve the critical path of a design. The following figure shows two examples of a large block RAM implemented with 512 RAMB36E5 primitives. The critical path is from a flip-flop to the ADDRARDADD* pin of every RAMB36E5 in the group.
- On the left, the example shows that the placer was unable to find the most optimal placement of the path, because block RAM utilization was high. RAMB36E5 primitives are marked in pink.
- On the right, the example shows that the placer was able to meet timing, because the RAMB36E5 blocks were grouped together. RAMB36E5 primitives are marked in light blue.
Figure 1. Critical Logic Grouping