Guiding an Implementation

During the design process your design may be modified and implemented many times. In most cases, parts of your design do not change from one implementation to the next. Guiding your design accelerates iterative implementations by reusing the unchanged sections from a previous implementation on current implementations. This is advantageous because the software spends time generating implementations only for sections of your design that have changed. The guide process is used during map, place, and route, and can significantly reduce design run times.

The guide process is more effective when the net names and instance names in your design remain constant between iterations, except for those specific parts of your design that are modified at the source level. This is generally true for schematic-based designs, but not for synthesis-based designs. For this reason, Xilinx does not recommend using guide for most synthesis-based designs.

Specifying a Guide Design

To select a previous implementation to guide a current implementation, select the following in the Design Manager.

Design Set Guide File(s)

The Set Guide File(s) dialog box appears. In the Guide Design field, you can select previously implemented revisions, Project Clipboard, Custom, or None.

• Project Clipboard
  
  The project clipboard is used to save the guide data of revisions that are overwritten. You can save guide data to the project clipboard by selecting the Copy Guide Data To Project Clipboard option in the Implement dialog box.
  
  
• Custom
  
  Use the Custom option to guide from any mapped, routed, or fitted file in your file system, including designs not generated from within the Design Manager. In the Custom dialog box, enter a mapped NCD file in the Mapping Guide File field. Enter a placed and routed NCD file in the Guide File field.
  
  
• None
  
  Select the None option if you do not want to guide your design.
  
  

Exact Guide Mode

When guiding in exact mode, the unchanged logic is not modified in any way. This mode is fastest, but least flexible. Use this mode if the design iteration requires only minor changes. Exact mode is the default value. It can be selected by having the Match Guide Design Exactly button pressed in the Options dialog.

Leveraged Guide Mode

When guiding in leveraged mode, the mapping, place, or route of the unchanged logic can be modified if the tools need to make layout changes to accommodate new logic. Use this mode if significant changes have occurred.

Leveraged mode is automatically selected when the Match Guide Design Exactly button is not selected in the Options dialog.