Set Clock Groups Dialog Box (set_clock_groups)

You access this dialog box by clicking Constraints > Set Clock Groups in the Timing Analyzer.

Allows you to specify which clocks in the design are unrelated.

The Timing Analyzer analyzes all clocks in a design as related, by default. The Set Clock Groups dialog box (and the set_clock_groups SDC command) allows you to specify unrelated clocks by creating smaller groups of related clocks.

Asynchronous clocks (-asynchronous) are completely unrelated: they have different ideal clock sources. Exclusive clocks (-exclusive) are not active at the same time, such as multiplexed clocks. The Timing Analyzer treats both types of clocks as if they were the same.

Specifying settings in this dialog box is equivalent to setting the set_false_path command for paths from each clock domain in every group to each clock domain in every other group. Specifying a single -group option results in the Timing Analyzer cutting this group of clocks from all other clocks in the design, including clocks that you might define in the future.

The following sections provide more information about specifying options for this constraint:

Group 1 (-group):

Allows you to specify the clocks to which the constraint applies. You can use the Name Finder (...) and the get_clocks option to build a collection Definition of clocks. Clocks specified in this group are cut from the clocks specified in the Group 2 box.

Group 2 (-group):

Allows you to specify the clocks to which the constraint applies. You can use the Name Finder (...) and the get_clocks option to build a collection Definition of clocks. Clocks specified in this group are cut from the clocks specified in the Group 1 box. If you leave this setting blank, then the clocks in the Group 1 box are cut from every other clock.