When closing a design for timing it is much more efficient and effective to also close a design from a power perspective simultaneously as this allows for the best run selection that satisfies both criteria. This can be done by simply adding the report power constraint to the script being run.
The following figure shows an example of how powerful this can be, for all 64-timing closure runs report power was also run, and these were all plotted together.
From the graph, 36 runs were timing clean and from a power perspective the total power budget is 77W. The 64 runs were in the range of 75W to 83W, an 8W or ~10% range.
Looking at the best run from a timing perspective, run #6 had a power estimate of 79.5W, which exceeds the total power budget. However from the timing clean runs, run #13 yielded the lowest power at 75W and was still timing clean.
So, understanding the design from both a timing and power perspective allows for the best run for both to be selected, without impacting the timing result and in this example enabled a 4W power saving.
