Add Net Constraint

The following content has been imported from Legacy Help systems and is in the process of being checked for accuracy.

Parent process: EditConstraints:AddConstraint

Applied parameters: Type=AddNet

Summary

This command is used to add or modify a constraint group targeting a specific net, within the active constraint file.

Details

First, ensure that the constraint file in which you wish to add or modify a Net constraint group, is open as the active view in the main design window.

After launching the command, the Add/Modify Net Constraint dialog will appear.

Adding a new Net constraint

If you wish to add a new Net constraint group to the file, simply type the name of the target net into the Target field.

There are two entries available for selection in the Constraint Kind drop-down field for this particular constraint target:

FPGA_GLOBAL - this constraint states that the targeted signal should be kept and use a high speed resource

FPGA_KEEP - this constraint prevents the targeted signal from being optimized.

In both cases, the corresponding Constraint Value can be either True or False.

After clicking OK a constraint group statement will be added to the constraint file. The statement will appear in the following form:

Record=Constraint | TargetKind=Net | TargetId=[Target field] | [Constraint Kind field]=[Constraint Value field]

For example, consider the case where you do not want the net STATUS_2 to be optimized. In the Add/Modify Net Constraint dialog, you would enter STATUS_2 into the Target field, select FPGA_KEEP as the Constraint Kind and then choose True in the Constraint Value field. The Net constraint group statement added to the file would be:

Record=Constraint | TargetKind=Net | TargetId=STATUS_2 | FPGA_KEEP=True

Modifying an existing Net constraint

If you wish to modify an existing Net constraint group within the file, simply enter the name of the net to be modified in the Target field.

If you want to modify the value for an existing constraint, select the entry for that constraint from the Constraint Kind drop-down field and then use the Constraint Value field to change the value as necessary.

If you want to add an additional constraint to the target net, simply use the Constraint Kind and Constraint Value fields to specify the constraint and its value respectively.

After clicking OK, the corresponding constraint group statement will be updated with the modified constraint information.

Notes

A constraint group is a single statement in a constraint file, targeting one or more objects and containing one or more specific constraints.

When adding a Net constraint group for the first time, the entry will appear below any other constraint group statements, where they exist.

When modifying an existing Net constraint group, the text cursor can be placed anywhere within the document - you do not have to place the cursor within the relevant line for the statement.

A Net constraint group can be added/modified by typing directly within the constraint file.

For more information about constraint files, refer to the application note 'Design Portability, Configurations and Constraints' and the 'Constraint File Reference', both of which can be found in the main FPGA Design section of the Help System.