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AR# 19445

10.1 Timing/PAR - I am incorrectly receiving "Warning:2797 (minimum frequency)" and "Warning:3234" on my DCM with no feedback

Description

When I run through PAR or perform a static timing analysis (Timing Analyzer or TRACE) on my design, the following warning occurs: 

 

"WARNING:Timing:2797 - The input clock user_CLKIN_IBUFG to DCM u1 has a period 

(frequency) specification of 100000 ps (10.00 Mhz). This violates the 

maximum period (minimum frequency) of 41670 ps (24.00 Mhz)." 

 

In most cases, the minimum frequency of a DCM is 24 MHz in low frequency mode. However, when CLKFX is used without CLKFB, the minimum frequency is 1 MHz. The above warning message is generated regardless of the CLKFB usage. Why?

Solution

This warning can be safely ignored if you are using only DFS outputs (CLKFX and CLKFX180) without a feedback on the DCM.  

 

This issue will be fixed in the next major design tools release.

AR# 19445
Date Created 09/03/2007
Last Updated 05/16/2014
Status Archive
Type General Article