FFT IP Core: User Guide

ID 683374
Date 11/06/2017
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3.4.2.1. Changing Block Size

To change the size of the FFT on a block-by-block basis, change the value of the fftpts simultaneously with the application of the sink_sop pulse (concurrent with the first input data sample of the block).
Table 6.   fftpts and Transform SizeThe value of the fftpts signal and the equivalent transform size.
fftpts Transform Size
10000000000 1,024
01000000000 512
00100000000 256
00010000000 128
00001000000 64
fftpts uses a binary representation of the size of the transform, therefore for a block with maximum transfer size of 1,024.
Always drive fftpts_in even if you are not dynamically changing the block size. For a fixed implementation drive it to match the transform length in the parameter editor.