Step 4: Using the Constraints Editor - 2022.2 English

Vivado Design Suite Tutorial: Using Constraints (UG945)

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2022.2 English
  1. Click Edit Timing Constraints from the Flow Navigator under the Synthesized Design section.

    The Vivado IDE displays the Timing Constraints window.

    There are three sections to the Timing Constraints window, as shown in the above figure:

    Constraints tree view
    Labeled as section A. This section displays standard timing constraints, grouped by category. Double-clicking a constraint in this section opens a form to help you define the selected constraint.
    Constraints Spreadsheet
    Labeled as section B. This section displays timing constraints of the type currently selected in the Constraints tree view. If you prefer, you can use this to directly define or edit constraints instead of using the Constraints wizard.
    All Constraints
    Labeled as section C. This section displays all the timing constraints that currently exist in the design.

    The Timing Constraints wizard identifies missing clocks, I/O delays, and clock domain crossings exceptions, but it does not handle general timing exceptions. You are going to use the timing constraints editor to create the exceptions that exist in this design.

    First, you are going to set a false path on the GTPRESET_IN input. This is the input constraint that you skipped by unchecking it on the input delay page of the Timing Constraints wizard. The GTPRESET_IN signal is an asynchronous reset that is properly synchronized inside the design. For more information about false paths, see this link in the Vivado Design Suite User Guide: Using Constraints (UG903).

  2. In the Constraints tree view, scroll down to the Exceptions category, shown in the following figure.
  3. Double-click Set False Path.

  4. To the right of the From text box, click the Choose Start Points button .

    The Specify Start Points dialog box appears.

  5. From the Find names of type drop-down list, select I/O Port as shown in the following figure.
  6. Under Options, select "Name", "contains" and in the search pattern text box, enter GTPRESET_IN.
  7. Click the Find button.
  8. Select GTPRESET_IN in the found results text box and press the right arrow to move it to the selected names text box.
    Tip: You can also double-click GTPRESET_IN to move it from the Find results list to the Selected names list.

    Notice that the Command field displayed at the bottom of the dialog box changes as you perform these different actions. The get_ports command changes to:

    get_ports "*GTPRESET_IN*"

  9. Click Set in the Specify Start Points dialog box.
    The completed Set False Path dialog box is shown in the following figure. Notice the following command text in the Command field at the bottom of the dialog box:
    set_false_path -from [get_ports "*GTPRESET_IN*"]

    The Vivado IDE displays the Tcl command form of all constraints created via the dialogs for your review. This is useful for learning the Tcl command syntax, and for verifying the final constraint before adding it.

  10. Click OK to close the Timing Constraint Editor.

    Vivado creates the false path exception.