ise map 时DCM警告

yangchao1t

WARNING:NgdBuild:1212 - User specified non-default attribute value (100.000000)
   was detected for the CLKIN_PERIOD attribute on DCM "dcm/dcm_sp_inst".  This
   does not match the PERIOD constraint value (110 ns.).  The uncertainty
   calculation will use the non-default attribute value.  This could result in
   incorrect uncertainty calculated for DCM output clocks.

请问这个警告是啥意义？