There are some configuration blocks in the FPGA that looks like gaps but are not a fence. The following figure highlights such a gap with a white rectangle. These blocks cannot be used as a fence. However, a valid BRAM PU fence has been shown with green rectangle.
Note: The following figure shows
the routing view in Vivado. It is highly recommended to always use device view in Vivado
to look at fences and create Pblocks while using IDF. The routing view is good for
determining PUs if needed.
Figure 1. Config Block Highlighted in White Rectangle Looks like a
Fence, but It Is Not
