No output from NCO IP - No drivers exist on out port

I'm trying to simulate a basic implementation of the NCO IP. However, I cannot get it to output anything.

I've provided an input to phi, asserted clken, waited a few clocks and de-asserted reset_n.

According to the timing diagram in the docs

I see I get some warnings when simulating my tb regarding the fsin_o and out_valid not having any drivers, which I suspect is the cause of the problem, but I can't work out why this is happening or how to fix it

Any help is much appreciated, thanks.