During analysis of critical paths, you might find multiple paths ending at control pins. You must analyze these paths to determine if there is a way to push the logic into the datapath without incurring penalties, such as extra logic levels. There is less delay in a path to the D pin than CE/R/S pins given the same levels of logic because there is a direct connection from the output of the last LUT to the D input of the FF. The following coding examples show how to push the logic from the control pin to the data pin of a register.
In the following example, the enable pin of dout_reg[0] has 2 logic levels, and the data pin has 0 logic levels. In this situation, you can improve timing by moving the enable logic to the D pin by setting the EXTRACT_ENABLE attribute to "no" on the dout register definition in the RTL file.
The following example shows how to separate the combinational and sequential logic and map the complete logic in to the datapath. This pushes the logic into the D pin, which still has 2 logic levels.
You can achieve the same structure by setting the EXTRACT_ENABLE attribute to “no.” For more information on the EXTRACT_ENABLE attribute, see the Vivado Design Suite User Guide: Synthesis (UG901).
