Iaddthe followingPERIOD constraintto the DCM/PLL/MMCM input clock in the UCF, but I received the followingmessage during Translate. This PERIOD constraint does not show up in the timing report, and no timing constraints are propagated through the DCM/PLL/MMCM.
What is the problem?
net "CLK_IN" TNM_NET = "CLK_IN";
TIMESPEC "TS_CLK_IN" = PERIOD "CLK_IN" 20ns HIGH 50%;
"WARNING:ConstraintSystem:190 - The TNM 'CLK_IN', does not directly orindirectly drive any flip-flops, latches and/or RAMS and cannot be activelyused by the referencing Period constraint 'TS_CLK_IN'. If clockmanager blocks are directly or indirectly driven, a new TNM and PERIOD arederived only if the PERIOD constraint is the only referencing constraint and if an output of the clock manager block drives flip-flops, latches or RAMs. This TNM is used in the following user groups and/or specifications:"
This warning indicates that the CLK_IN group does not contain any endpoints (flip-flops, latches, RAMS, etc.) and the PERIOD constraint will not be propagated through the DCM/PLL/MMCM because the CLK_IN group is used not only in the PERIOD constraint, but also in other timing constraints. For example:
TIMESPEC TS_1 = FROM "CLK_IN" TO "group1" TIG;
TIMEGRP "group2" = RISING "CLK_IN";
So the PERIOD constraint will be ignored.
The PERIOD constraint of the DCM/PLL/MMCM input clock will be propagated to the output clocks only when the following conditions are met:
To resolve this problem, use either of the following two methods: