FFT filter in Simulink

Hi Everyone,

I'm trying to make a custom signal filter in Simulink and rather than just making a lowpass/highpass/Bandpass block model I've decided to convert my signal using an FFT and IFFT to combine all three into a single block with no effect on the amplitude.

I'm currently using MATLAB R2009b 64-bit (7.9.0) with NO TOOLBOXES. Because of this I need to code the FFT and IFFT conversion for Simulink. However to do this I need to change the signal to N-points. The code I made will do all the calculations needed for a given signal and works quite well but I need to have some N number of previous data points feeding into the embedded m-file.

What I need help with is to create something that will cutoff/duplicate the last second of code into a time-vector to feed into my code. I can't use a-ton of unit-delays due to the variable step size needed for the rest of my code not to mention the cumbersomeness of it all; and I don't know how else to make this or other block that would be useful in this situation which I can access without any additional Toolboxes.

If anyone has ideas I'm all ears.

Thank you

Joe