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AR# 30333

10.1 NGDBUILD - Problems with constraint precedence

Description

Keywords: ucf, ncf, area group, loc, pin, bank



After upgrading to ISE 10.1, the constraints in my design do not behave the way they did in 9.2i. In particular, I'm seeing the following warning message. What could be the reason for this?

WARNING:NgdBuild:1012 - The constraint <NET "XT_SPI4_TDAT_P[9]" LOC = AN38;>
[vh2.ucf(440)] is overridden on the design object XT_SPI4_TDAT_P[9] by the
constraint <INST "XT_SPI4_TDAT*" LOC = "Bank17";> [vh2.ucf(1308)].

A new constraints subsystem is being introduced in ISE 10.1 and a few problems have been identified. In general, problems are that order of processing (last constraint wins) is causing one constraint to override another, instead of the expected behavior where the more specific constraint takes precedence.

The known issues that have been identified with order dependency are:
- BANK constraint overrides a pin LOC constraint.
- BANK constraint overrides a pin IOSTANDARD constraint.

In a similar issue, a PERIOD constraint specified in a UCF file was overridden by an NCF file PERIOD constraint. UCF constraints should take precedence.

Solution

These problems are being investigated for a service pack fix. Meanwhile, the order dependent issues can be avoided by rearranging the UCF constraints so that the constraints that should take precedence are moved to the end of the file.

AR# 30333
Date Created 02/22/2008
Last Updated 02/26/2008
Status Active
Type General Article