Design closure consists of meeting all system performance, timing, and power requirements, and successfully validating the functionality in hardware. During the design closure phase where you are starting to run the design through the implementation tools, both timing and power considerations should be your top priorities.
At this stage of design closure, estimation of design utilization, timing and power gain more accuracy. This presents an opportunity to reaffirm that the timing and power goals are achievable. To confirm the design can meet its requirements, Xilinx recommends conducting both a timing and power baseline. A timing baseline is largely about evaluating timing paths after accurate timing constraints have been defined. A power baseline needs to provide Vivado with the right toggle information to determine accurate dynamic power information.
By combining the analysis of power requirements and timing requirements, if one item is off significantly, a measure taken to resolve it can significantly impact the other. For example:
- An extreme measure might be necessary to meet a power budget such as scaling back features. This will make timing closure significantly easier as the part is less congested.
- A less extreme measure might involve adding logic to reduce switching. This might make timing closure more difficult, particularly if in a congested area of the die.
While many power saving items do not impact timing closure, it is possible that other items might make timing closure harder. Applying the required power saving techniques early will help you understand the true magnitude of the timing closure task.
Once you start to iterate from the baseline, you should recheck the power numbers when you make an improvement to timing. This ensures that you understand what change caused a regression. Generally, turning on wholesale power saving features early and then scaling back on individual items that are causing timing issues helps to strike the right balance of meeting design closure goals.
Conducting both power and timing analysis together and early in the design closure implementation phase will save engineering time and enable more accurate project planning. In addition, it creates time to allow engineering solutions to be explored than when this is realized later in the design cycle.