Why are my results incorrect when I use the Radix-2 Lite implementation with the block floating point option?
The problem is that the block floating point unit is not being properly reset at the end of a transform.
This is fixed in the Fast Fourier Transform (xFFT) v4.1.
The way to work around this issue is to assert the sclr pin before each transform to ensure that the block floating point unit is reset.
See (Xilinx Answer 29209) for a detailed list of LogiCORE Fast Fourier Transform (FFT) Release Notes and Known Issues.