The following warning occurs during the Post-PAR static timing analysis:
"WARNING:Timing:3391 - Timing constraint< OFFSET IN constraint>does not specify a data valid duration and will not be hold checked. To enable hold checking on this offset constraint please specify a data valid duration using the VALID < duration > option."
What does this mean?
The Timing Analyzer can perform setup and hold checks for OFFSET IN constraint. However, the hold checkis performed only when a VALID value is specified in the OFFSET IN constraint.
OFFSET = IN 3 ns BEFORE "clk_in";
NET "wren"OFFSET = IN 3 ns BEFORE "clk_in";
TIMEGRP "wr_grp"OFFSET = IN 3 ns BEFORE "clk_in";
If the VALID value is not specified in the OFFSET IN constraint, the hold check will not be performed and a fast path setup calculation (at the slow corner)is performed instead; see (Xilinx Answer 42701)for more information.
To remove this warning, add VALID value in the OFFSET IN constraint.