Incremental Design Modes

This section describes recommended Incremental Design modes for new and existing designs. Before running any Incremental Design mode, your design should meet timing requirements without using Incremental Design.

Incremental Enabled Mode

The Incremental Enabled Mode conveys that special considerations must be followed during the MAP process. MAP normally performs certain optimizations across the design, regardless of defined AREA GROUP boundaries. To ensure that MAP respects the same set of boundaries that synthesis has, it must know that the design will be used in Incremental Guide Mode. Therefore, Incremental Enabled Mode, which uses the -gm incremental option, informs MAP of this process. This ensures that later, when guide mode is entered, MAP will not optimize the design with a different set of rules, and allows the last Incremental Enabled result to be a valid guide file.

After design changes are limited to one or two logic groups, or timing is met on critical timing logic groups, use the MAP and PAR results from a previous implementation as the Incremental Design Guide files.

Note: It is important that your design follow good hierarchical design methodologies and meet timing requirements before running an Incremental Design flow. Incremental Design should not be used to solve timing issues.

Setting Up Incremental Enabled Mode in Project Navigator

Right-click on the Implement Design item in the Processes for Source window.

Click Incremental Design Properties in the Process Properties dialog.

Check the Enable Incremental Design Flow checkbox.

Setting Up Incremental Enabled Mode using the command line

For running Incremental Design from the command line, do the following to set up Incremental Enabled Mode:

Set the -gm incremental option and argument on both the MAP and PAR command lines.

Incremental Guide Mode

In Incremental Guide Mode, MAP determines what logic has changed and informs PAR that the changed logic must be reimplemented.

Setting Up the Incremental Guide Mode for Project Navigator

Right-click the Implement Design item in the Processes for Source window.

Click Incremental Design Properties in the Process Properties dialog. The Enable Incremental Design Flow checkbox should already be checked, thus setting the MAP and PAR Guide Mode values to Incremental.

Select Run Guided Incremental Design Flow to set the MAP and PAR guide files to use the results from the previous iteration by default.

If you are setting the guide files to another set of results for guiding, then follow these directions:

Next to MAP Guide Design File (.ncd), browse to and select another_map_design.ncd.

Note: Make sure that the .ngm file is the same name as another_map_design.ncd. This file will automatically be read in if it has the same name as the mapped .ncd file.

Next to PAR Guide Design File (.ncd), browse to and select another_par_design.ncd.

Setting Up Incremental Guide Mode for the Command Line

For MAP:

Rename the mapped .ncd and .ngm files from the previous implementation to something like the following:

Make sure that both files have the same name, or the .ngm file will not be read and guide mode will fail.

Add -gf <design_name>_map_guide.ncd to the previously used options, including the -gm incremental option.

For PAR:

Rename the placed and routed .ncd file from the previous implementation to something like the following:

Add the -gf <design_name>_par_guide.ncd to the par options, including the -gm incremental option.

Rules for External Changes that can cause Logic Group Reimplementation

The following is a list of rules to follow to prevent the inadvertent reimplementation of a logic group during Incremental Guide Mode.

Do not change AREA GROUP RANGEs

Do not change MAP switches

Do not change the design or AREA GROUP compression factors

Do not change either the PLACE, GROUP or MODE properties for a logic group

Situations for Forcing a Reimplementation of a Logic Group

When timing constraints that affect a logic group are changed, you should either not guide the current iteration or use the following:

After the iteration is done, guiding may resume as normal or IMPLEMENT should be removed or changed from FORCE to AUTO, depending on which method was used.