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AR# 37782

12.2 Timing - WARNING:ConstraintSystem - TNM : clock was distributed to a DCM

Description

I see the following warning message in my design and want to know what it means?

WARNING:ConstraintSystem - TNM : clock was distributed to a DCM but new TNM
constraints were not derived. The requirement for derived TNM constraints is
that the distributed TNM is referenced by no more than a single PERIOD
constraint. Non-PERIOD referencers are also not allowed. This TNM is used in
the following user groups or specifications:
TIMESPEC "TS_clk1" = FROM "clock" TO "clockb" 20ns DATAPATHONLY; [top.ucf(13)]
TIMESPEC "TS_clk2" = FROM "clock" TO "clockc" 40ns DATAPATHONLY; [top.ucf(14)]

Solution

This warning signifies that you have TNM group that is used within a PERIOD constraint and is also used in one or more FROM-TO constraints. Having this TNM Group used in FROM-TO constraints stops the tools from propagating the PERIOD constraint.

The resolution is to create two TNM Groups for your input clock. One used for the FROM-TO constraints and the other for the PERIOD propagation.

Please see the constraint guide page 172 for more information on the restrictions for PERIOD constraint transformation:
http://www.xilinx.com/support/documentation/sw_manuals/xilinx12_1/cgd.pdf

If the TNM group for the FROM-TO constraint is independent of the TNM group for the PERIOD, then the warning message is informing you that the TNM group for the FROM-TO constraint will not be propagated through the DCM/PLL/MMCM component.
AR# 37782
Date Created 10/13/2010
Last Updated 02/18/2013
Status Active
Type General Article
Tools
  • ISE Design Suite - 12.1
  • ISE Design Suite - 12.2
  • ISE Design Suite - 12.3