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AR# 29560

LogiCORE Fast Fourier Transform (FFT) v4.0 - The overflow flag does not assert when an overflow occurs in my 64- or 128-point FFT. Why?

Description

The overflow flag does not assert when an overflow occurs in my 64- or 128-point FFT. Why is this the case?

Solution

This is a known problem that is fixed in the FFT v5.0. 

 

The overflow issue occurs only when the following core conditions occur: 

 

Device Family: Spartan-3/E/A/AN, Virtex-II/II Pro/4 

FFT Architecture: Pipelined Streaming I/O 

Scaling Options: Scaled 

Overflow: Yes 

Output Ordering: Natural order output 

Transform Length: 64- or 128-point transform 

Number Of Stages Using Block RAM: 0 

 

You can work around the problem by using the Digit Reversed output ordering and using a RAM buffer to externally reorder the FFT outputs. 

 

Please see (Xilinx Answer 29209) for a detailed list of LogiCORE Fast Fourier Transform (FFT) Release Notes and Known Issues.

AR# 29560
Date Created 10/28/2007
Last Updated 05/20/2014
Status Archive
Type General Article