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AR# 17622

Partial Reconfiguration - How should I use VCC/GND in my module-based partial reconfiguration design?

Description

General Description: 

What is the proper way to create and/or use VCCs and GNDs in my reconfigurable module for partial reconfiguration?

Solution

Due to the unique circuitry of the FPGA architecture for VCCs, constants should not be driven from VCC or GND sites in a reconfigurable module to correctly retain their values during active partial reconfiguration. The ideal way to drive constant values in a reconfigurable module is to use LUT sources. Recent versions of the ISE software do this automatically with the use of the following constraints: 

 

ISE 5.x: 

AREA_GROUP "AG_reconfig" ROUTE_AREA = RECONFIG DISALLOW_BOUNDARY_CROSSING RECONFIG_MODE; 

 

ISE 6.x: 

AREA_GROUP "AG_reconfig" MODE=RECONFIG; 

 

If you are using an older software version, a LUT can be instantiated for use as a constant source. To verify that your constant signals have been implemented correctly, verify that no VCC or GND sites are included in your reconfigurable module through the use of FPGA Editor.

AR# 17622
Date Created 09/03/2007
Last Updated 05/15/2014
Status Archive
Type General Article