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AR# 31983

10.1 MAP/PAR - Design implementation fails with reference to constraint that does not exist in the source files

Description

When I run my design through the implementation tools, I get the an error referencing a constraint that previously existed in my sources files but no longer does. For example:

ERROR:Place:382 - The placer was unable to find a feasible solution for the IOBs in your design. This is possibly due to SelectIO banking constraints.

Each Group of a specific Standard is listed.

Standard LVCMOS25 (Vref=NR Vcco=2.50 Terminate=none) 10 IOs, 1 locked.

Why is this constraint still active? What can I do to clear this constraint from my design?

Solution

This is a known issue with the ISE 10.1 implementation tools, where a constraint database is sometimes not correctly updated to reflect the removal of a constraint. The phantom constraint is contained in a directory structure in your project directory named project_xdb, where "project" is the name of your project. This problem can be worked around by removing the project_xdb directory before rerunning the implementation tools.

This problem is scheduled to be fixed in ISE version 11.1.

AR# 31983
Date Created 12/11/2008
Last Updated 12/15/2012
Status Active
Type General Article