I'm not an expert in the DSP side of the product, but my understanding of your code is that you are invoking the same object twice in a single time step. You have a single dsp.HDLIFFT named ifft128 in your design. Each time that your function mainfc is called will correspond (in the simple case) to a single hardware clock cycle. In this single cycle you are calling the step function on ifft128 twice. This function can be thought of as the behavior of the IFFT implementation. So, in essence, you are attempting to run the same FFT twice in one cycle. This is not supported for HDL code generation for fairly straightforward reasons, although MATLAB has no issues executing the code that you have written. HDL Coder does not perform enough semantic analysis to notice that the two calls to step() are mutually exclusive from each other.
Your code looks easy to update. You need to make one call to your wrapper function:
[Xt,validOut]=ifft128_fc(ifft128,out1, st == 0);
If st can be any value besides 0 or 1, you may want to enclose this call inside the appropriate if statement:
if st == 0 || st == 1
[Xt,validOut]=ifft128_fc(ifft128,out1, st == 0);
end
