11.1 Timing, Virtex-4 - "WARNING:Timing:3327 - Timing Constraint" - Component Switching Limit is limited by DLL portion of the DCM when both DLL and DFS DCM outputs are used

AR#	33007	Search For Another Answer
Topic	SW-Timing Analyzer/TRCE
Last Updated	06/26/2009
Status	Active

Description

Keywords: Timing, DCM, Timing Analysis, DLL, DFS, Virtex-4

In Virtex-4 designs, using both the DLL and DFS outputs of a DCM show the following warning (depending on clock frequency):

"WARNING:Timing:3327 - Timing Constraint *** fails the minimum period check for the input clock because the period constraint value *** is less than the minimum internal period limit of ***. Please increase the period of the constraint to remove this timing failure."

When is this going to be fixed?

Solution

This is expected behavior of the timing analysis. If both DLL and DFS outputs are used, follow the more restrictive specifications. The CLKIN_FREQ_FX_LF/HF_MIN/MAX should always be used to determine DFS_FREQUENCY_MODE (no matter whether or not DLL outputs are also used).