21.7.11 Specifying an Input Delay Constraint

Use the input delay constraint to define the arrival time of an input relative to a clock.

To specify an input timing delay constraint:

  1. Add the constraint in the Editable Constraints Grid or open the Set Input Delay Constraint dialog box using one of the following methods:
    • From the SmartTime Actions menu, choose Constraints > Input Delay.
    • Click the þÿ icon.
    • Right-click the Input Delay in the Constraint Browser.
    • Double-click any field in the Input Delay Constraints grid.
      The Set Input Delay Constraint dialog box appears (as shown below).
      Figure 21-35. Set Input Delay Dialog Box
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  2. Select either External Setup/Hold or Input Delay.
    • External Setup/Hold enables you to enter an input delay constraint by specifying the timing budget inside the FPGA using the external setup and hold time. This is the default selection.
      Note: The external hold information is currently used for analysis only and not by the optimization tools.

      For the basic timing analysis flow of a simple design, select External Setup/Hold.

    • Input Delay enables you to enter an input delay constraint by specifying the timing budget outside the FPGA. You can enter the Maximum Delay, the Minimum Delay, or both.
      Note: The Minimum Delay is currently used for analysis only and not by the optimization tools.

    When you change values in one view, SmartTime automatically updates the other view.

  3. Specify the Input Port or click the Browse button to display the Select Ports for Input Delay dialog box.
    Figure 21-36. Select Ports for Input Delay Dialog Box
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  4. Select the name of the input pin(s) from the Available Pins list. Choose the Pin Type from the drop-down list. You can use the filter to narrow the pin list. You can select multiple ports in this window.
  5. Click Add or Add All to move the input pin(s) from the Available Pins list to the Assigned Pins list.
  6. Click OK.
    The Set Input Delay Constraint dialog box displays the updated Input Port information.
    Figure 21-37. Updated Set Input Delay Constraint Dialog Box
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  7. Select a clock from the Clock Port drop-down list.
  8. If you selected Show by: External Setup/Hold, specify the External Setup. If you selected Show by: Input Delay, specify the Maximum Delay value.
  9. If you selected Show by External Setup/Hold, specify the External Hold. If you selected Show by: Input Delay, specify the Minimum Delay value.
  10. Click OK.

SmartTime adds this constraint to the Constraints List in the SmartTime Constraints Editor.