Problems about sink_ready and sink_valid in FFT IPCore

Hi,

I'm trying to test FFT mega core v8.1 with ModelSim and meeting some problems about the signals.When using The FFT_tb.v generated by FFT MegaCore,the results are correct.But when using the tb file written by me in which I do not assert the sink_valid right after assert the reset_n(sink_valid asserted serval cycles after sink_ready asserted),the results are not completely correct.But I think it is not necessary to assert sink_valid at the moment sink_ready asserted.

Does anyone can tell me how to deal with these problems?

Thank you!