A path starting with one clock is not analyzed by a period constraint when the endpoint is a phase shift pin of the DCM (such as PSINCDEC). The two clocks are related, and using a FROM:TO constraint on the two clock groups does not work. How do I constrain these paths?
To work around this problem, use a TPSYNC on the DCM pin in a FROM:TO constraint as follows:
NET "clka" TNM_NET = "clka";
PIN dcm_name.PSINCDEC TPSYNC = "syncpoint";
TIMESPEC "TS_crosssync" = FROM "clka" TO "syncpoint" 20 ns;