Review the placement of the cells in the design. Compare two I/O reports to review the I/O placement and I/O standards. Make sure all the I/Os are placed. A simple search finds all I/Os without fixed placement as shown in the following figure.
Figure 1. I/O Is Not Fixed
If clock skew has changed between the runs, consider re-using the clock primitive placement from the run that met timing. The Clock Utilization Report lists the placement of the clock tree drivers, as shown in the following figure.
Figure 2. Clock Locations
The LOC constraints can easily be copied into your XDC constraints file.
Many designs have met timing by reusing the placement of the Block RAMs and DSPs. Select Edit > Find to list the instances.
Figure 3. DSP or RAM
