FFT

Files
file	e_fft.c
	Package to mange the FFT.
file	e_fft.h
	Package to mange the FFT.
file	e_fft_utilities.h
	Some fft features.
file	e_input_signal.c
	Allocate memory and initialize the sigCmpx array.
file	e_twiddle_factors.c
	The FFT factor from Microchip.

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Detailed Description

Introduction

The fast fourier transform (FFT) is really usefull, especially to work with the microphones data. This package contains all you need to perform the FFT.
The dsPic has some specials instructions (MAC instructions) which are used here.

How it works

To do the FFT on your data, first make this:

• choose the size of the array in which the FFT will be done. You have to choose one of the following values: 64, 128, 256 or 512.
• put your choice in the FFT_BLOCK_LENGTH (it's in the file e_fft.h).

Then you just have

• to copy your data in the sigCmpx array with the e_fast_copy(int* in_array, int* out_array, int size) function
• to call the e_doFFT_asm(fractcomplex* sigCmpx) function

A little code to illustrate this.

        e_ad_scan_on();
        // waiting all the 512 data (here we scan the microphones)
 while(!e_ad_is_array_filled());
        e_ad_scan_off();

        // We put the mean to zero
        e_subtract_mean(e_mic_scan[0], FFT_BLOCK_LENGTH, LOG2_BLOCK_LENGTH);
        // We copy the array of micro zero to the FFT array
        e_fast_copy(e_mic_scan[0], (int*)sigCmpx, FFT_BLOCK_LENGTH);
        
        // The result is saved => we can launch a new acquisition
        e_ad_scan_on();
        // Now we are doing the FFT
        e_doFFT_asm(sigCmpx);

Author:

Doc: Jonathan Besuchet

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