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AR# 34294

14.x Timing Analysis - "WARNING:Timing:3379 - The REFERENCE_PIN xxx on constraint xxx ... was not included as part of analysis"


I have this OFFSET OUT constraint in my UCF:

TIMEGRP "pad_group" OFFSET = OUT 7.69ns after "ClkIn" REFERENCE_PIN "ClkOut" TIMEGRP "reg_group";

However, I receive the following warning during Process "Generate Post-Place & Route Static Timing":

WARNING:Timing:3379 - The REFERENCE_PIN ClkOut on constraint TIMEGRP "pad_group" OFFSET = OUT 7.69 ns AFTER COMP "ClkIn" REFERENCE_PIN BEL"ClkOut" TIMEGRP reg_group; was not included as part of analysis. The REFERENCE_PIN keyword is being ignored.

How can I resolve this issue?


Solution 1: Use group specific OFFSET OUT

To use REFERENCE_PIN keyword in the group specific OFFSET OUT constraint, the following requirements must be met.

  • The reference output clock (ClkOut) must be a regenerated clock using an ODDR or any other sequential element.

In a source-synchronous design, a typical usage is regenerating the output clock using an ODDR. The REFERENCE_PIN keyword will not work if the reference output clock pad is directly connecting from BUFG or the clock source (input clock pad or DCM/PLL/MMCM output clock).

  • The reference output clock pad must be included in the same pad group of output data pads.
  • The reference output clock ODDR must be included in the same register group of output data registers.

Example 1:

#create pad group and include the output clock pad into the same group

NET "<data_pad_name_pattern>" TNM = pad_group;

NET "ClkOut" TNM = pad_group;

#create register group and include the output clock ODDR into the same group

INST "<data_registers_name_pattern>" TNM = register_group;

INST "ClkOutODDR" TNM = reg_group;

#write OFFSET OUT constraint

TIMEGRP "pad_group" OFFSET = OUT AFTER "Clkin" REFERENCE_PIN "ClkOut" TIMEGRP "reg_group";

Solution 2 : Use global OFFSET OUT

The reference output clock (ClkOut) must be a regenerated clock using an ODDR or any other sequential element as well when using global OFFSET OUT with REFERENCE_PIN keyword.

Example 2:

#write the global OFFSET OUT constraint.


AR# 34294
Date Created 02/16/2010
Last Updated 01/14/2014
Status Active
Type General Article
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