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AR# 13721

12.1 Known Issue - Timing - "WARNING:Timing:2491 - No timing constraints found, doing default enumeration"

Description

When I perform a static timing analysis, the following warning occurs: 

 

"WARNING:Timing:2491 - No timing constraints found, doing default enumeration." 

 

What does this warning mean? Is it serious? How do I avoid it?

Solution

Static timing analysis is performed by analyzing a design against the user-specified timing constraints. Without constraints, the static timing tools would have little to report. If the timing tools are not given any constraints, the system automatically creates common constraints through a process called default enumeration, and it analyzes the design against these constraints. (This is similar to advanced analysis (-a) in TRACE, or Analyze -> Analyze Against Auto-Generated Constraints in Timing Analyzer.) 

 

This process can be useful for obtaining a quick estimate of a design's performance. However, you should constrain your designs for higher Quality of Results (QoR) during the place-and-route process.  

 

For information on how to constrain a design, use the Xilinx Constraints Editor.

AR# 13721
Date Created 08/29/2007
Last Updated 05/14/2014
Status Archive
Type Known Issues