Guiding a Design

You can select a previously mapped, routed, or fitted implementation revision to use as a guide for implementation. You can also guide from the revision data copied to the project clipboard or from a guide file. The procedure for guiding your implementation is the same for FPGAs and CPLDs. However, guide algorithms differ between the two.

When guiding an FPGA design, the software attempts to use the guide for mapping and placing logic and routing signals for the current implementation revision of the design. This can reduce the amount of time the software takes to place and route. Guiding a design for an FPGA works as follows.

• If a component in the new design has the same name as that of the guide design or file, it is placed as in the guide.
  
  
• If an unnamed component in the new design is the same type as a component within the guide, it is placed as in the guide.
  
  
• If the signals attached to a component in the new design match the signals attached to the component of the guide, the pins are swapped to match the guide, where possible.
  
  
• If the signal names in the input design match the guide, and have the same sources and loads, the routing information from the guide design is copied to the new design.
  
  

After these components and signals are placed and routed, the remainder of the logic is placed and routed. If you have made only minor changes to your design and want the remaining logic placed and routed exactly as in your guide design, select the Match Guide Design Exactly option. This option locks the placement and routing of the matching logic so that it cannot change to accommodate additional logic.

For CPLDs, each time you implement your design, a guide file is created (design_name.gyd) which contains your pinout information. You can reuse this file in subsequent iterations of your design if you want to keep the same pinouts. If you select a valid implementation revision, guide file name, or the project clipboard, the pinouts from that file will be used when the design is processed.

NOTE

You can override guide file locations by assigning locations in your design file or constraints file.

To Specify a Guide Design

1. In the Design Manager project view, select an implementation revision icon.
   
   
2. Select Design Set Guide File(s) from the Design Manager.
   
   The Set Guide File(s) dialog box appears, as shown in the “Set Guide File(s) Dialog Box” figure of the “Menu Commands” chapter.
   
   
3. Select a guide design from the Guide Design drop-down list.
   
   
   • Select an existing implementation revision.
     
     
   • Select None if you do not want to guide the design.
     
     
   • Select Project Clipboard to guide from the implementation revision copied to your project clipboard. If no data exists in the clipboard or if you want to copy new data to the clipboard, use the Copy guide data to project clipboard option in the Implement dialog box. This dialog box is described in the “Implement Dialog Box Options” section of the “Menu Commands” chapter.
     
     
   • Select Custom to guide from any mapped, routed, or fitted file in your file system, including designs not generated from within the Design Manager. This option invokes the Custom dialog box, shown in the “Custom Dialog Box (Guide Files)” figure of the “Menu Commands” chapter, in which you can specify your guide file. Choose an NCD file for FPGAs or a GYD file for CPLDs. You can also specify a mapping guide file for FPGAs.
     
     

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     NOTE

     The implementation revision or revision data is based on a placed and routed design. To guide from a mapped file, you must use the Custom option.

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4. For FPGA devices, select Match Guide Design Exactly if you want to lock the placement and routing of matching logic.
   
   For synthesis-based designs, use the Match Guide Design Exactly option only if the guide file is from the same design version.
   
   

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   NOTE

   If you do not select this option, the guide files are used as a starting point only. This allows the mapper, placer, and router greater flexibility in accommodating design modifications, often resulting in greater overall success.

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5. Click OK.
   
   When you implement the design, the Flow Engine uses the specified file to guide the implementation.