The following warning occurs in NGDBuild:
"WARNING:NgdBuild:477 - clock net '%s' has non-clock connections Xvendor=%s Xleid=%d Xhiername=%s."
Ensure that the clock signal is connected to synchronous elements on the clock pin.
When a BUFG or BUFGP is driving non-clock pins, the warning points out non-clock connections on the clock tree. These connections can result in timing constraint overlap and gated clocks; the warning is issued to help you avoid these problems.