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AR# 18392

12.1 Timing Analysis - Clock Paths covered by OFFSET constraint are appearing in the unconstrained path report


My design is completely constrained. I have OFFSET constraints on all my input and output registers, but paths are still appearing in the unconstrained path report. The paths that appear are my clock paths from the clock pad to the input and output registers. As the OFFSET constraint uses the Data Path and Clock Path to calculate its value, I am assuming the clock path is constrained by this constraint.


OFFSET constraints (OFFSET/IN and OFFSET/OUT) cover only data paths. These constraints do use the Clock Path to calculate the OFFSET values, but do not actually constrain them. You can constrain these paths with a FROM:TO constraint, but it should not be necessary (especially for clocks on Global Routing).

In case the design requires to have the Clock path constrained, please find below an example to remove the Clock path from the Unconstrained path analysis section.

INST "abc_inst" TPTHRU = abc_grp;

// where abc_inst is the instance name of a MMCM/PLL/DCM/BUFR/BUFIO ...

TIMESPEC ts_ignore_clock = FROM PADS THRU "abc_grp" TIG;

AR# 18392
Date Created 09/03/2007
Last Updated 05/12/2012
Status Active
Type Known Issues
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