Clock Relationship Summary

The Clock Relationship Summary section lists the related clocks, their constraints, and the slack. The report shows measurements using the active clock edge. The number in the Slack (ns) column shows you how much margin you have for each clock relationship. The Edge column shows the active edge for the launch and capture clocks. R is rising edge triggered and F is falling edge triggered.

Important: If any of the clock relationships have negative slack, your design has not closed timing.

A timing path with negative slack indicates that there is insufficient time for the signal to arrive, resulting in design instability. When trying to close timing, do not adjust the clock period. Instead, adjust the constraints in your SDC file or modify your design.

Tip: You can quickly see if your design has closed timing in the Result pane in the Timing section. If the Least Slack number is negative, the design did not close timing.

Did My Design Close Timing?

This summary shows that the design has not closed timing because the slack for the Fclk to Fclk relationship is negative (-0.875).

---------- 2. Clock Relationship Summary (begin) ----------

Setup (Max) Clock Relationship
  Launch Clock    Capture Clock   Constraint (ns)     Slack (ns)          Edge
      Oclk             Oclk          99999.992        99999.408          (R-R)
      Fclk             Fclk              6.400           -0.875          (R-R)
      Sclk             Sclk             12.800           11.762          (R-R)

Hold (Min) Clock Relationship
  Launch Clock    Capture Clock   Constraint (ns)     Slack (ns)          Edge
      Oclk             Oclk            0.000            0.101            (R-R)
      Fclk             Fclk            0.000            0.070            (R-R)
      Sclk             Sclk            0.000            0.109            (R-R)

NOTE: Values are in nanoseconds.

---------- Clock Relationship Summary (end) ---------------