General Description: In the schematic, clock output of BUFG goes to the CLK pin of STARTUP as well as other FFs. One would get warning message in MAP: WARNING:x4kma:78 - STARTUP symbol "$I1" (output signal=<none>) conflicts with other symbol connections on the clock signal. The symbol cannot be connected to the clock signal based on the location constraint placed on its clock buffer.
解决方案
This is an incorrect message and can be safely ignored. The startup pin clock does get connected. The warning message has to do with the fact that the startup clock pin can only be reached by using a route-thru.