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AR# 39712

13.x Constraints System - "WARNING:ConstraintSystem:190..."

Description

Iaddthe followingPERIOD constraintto the DCM/PLL/MMCM input clock in the UCF, but I received the followingmessage during Translate. This PERIOD constraint does not show up in the timing report, and no timing constraints are propagated through the DCM/PLL/MMCM.

What is the problem?

Constraint:

net "CLK_IN" TNM_NET = "CLK_IN";

TIMESPEC "TS_CLK_IN" = PERIOD "CLK_IN" 20ns HIGH 50%;

Message:

"WARNING:ConstraintSystem:190 - The TNM 'CLK_IN', does not directly orindirectly drive any flip-flops, latches and/or RAMS and cannot be activelyused by the referencing Period constraint 'TS_CLK_IN'. If clockmanager blocks are directly or indirectly driven, a new TNM and PERIOD arederived only if the PERIOD constraint is the only referencing constraint and if an output of the clock manager block drives flip-flops, latches or RAMs. This TNM is used in the following user groups and/or specifications:"

Solution

This warning indicates that the CLK_IN group does not contain any endpoints (flip-flops, latches, RAMS, etc.) and the PERIOD constraint will not be propagated through the DCM/PLL/MMCM because the CLK_IN group is used not only in the PERIOD constraint, but also in other timing constraints. For example:

TIMESPEC TS_1 = FROM "CLK_IN" TO "group1" TIG;
TIMEGRP "group2" = RISING "CLK_IN";

So the PERIOD constraint will be ignored.

The PERIOD constraint of the DCM/PLL/MMCM input clock will be propagated to the output clocks only when the following conditions are met:

  • The DCM/PLL/MMCM output clocks drive synchronous elements (flip-flops, latches, RAMS, etc.).
  • The group associated with the PERIOD constraint is used in exactly ONE PERIOD constraint.
  • The group associated with the PERIOD constraint is NOT used in any other timing constraints, including FROM:TO (Multicycle), or OFFSET constraints.
  • The group associated with the PERIOD constraint is NOT referenced or related to any other user group definition.

To resolve this problem, use either of the following two methods:

  • Do not use the CLK_IN group in any other timing constraints; use an alternate way instead.
  • Manually create PERIOD constraints for the DCM/PLL/MMCM output clocks.
AR# 39712
Date Created 10/07/2011
Last Updated 05/19/2012
Status Active
Type Error Message
Tools
  • ISE - 10.1
  • ISE Design Suite - 11.1
  • ISE Design Suite - 11.2
  • More
  • ISE Design Suite - 11.3
  • ISE Design Suite - 11.4
  • ISE Design Suite - 11.5
  • ISE Design Suite - 12.1
  • ISE Design Suite - 12.2
  • ISE Design Suite - 12.3
  • ISE Design Suite - 12.4
  • ISE Design Suite - 13.1
  • ISE Design Suite - 13.2
  • ISE Design Suite - 13.3
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