CCS/TM4C123GH6PM: arm_fft_bin_example_f32 code: How the conversation of bin to frequency is done?

#include "arm_math.h"

#include "arm_const_structs.h"


#define TEST_LENGTH_SAMPLES 2048


/* -------------------------------------------------------------------

* External Input and Output buffer Declarations for FFT Bin Example

* ------------------------------------------------------------------- */

extern float32_t testInput_f32_10khz[TEST_LENGTH_SAMPLES];

static float32_t testOutput[TEST_LENGTH_SAMPLES/2];


/* ------------------------------------------------------------------

* Global variables for FFT Bin Example

* ------------------------------------------------------------------- */

uint32_t fftSize = 1024;

uint32_t ifftFlag = 0;

uint32_t doBitReverse = 1;


/* Reference index at which max energy of bin ocuurs */

uint32_t refIndex = 213, testIndex = 0;


/* ----------------------------------------------------------------------

* Max magnitude FFT Bin test

* ------------------------------------------------------------------- */


int32_t main(void)

{


arm_status status;

float32_t maxValue;


status = ARM_MATH_SUCCESS;


/* Process the data through the CFFT/CIFFT module */

arm_cfft_f32(&arm_cfft_sR_f32_len1024, testInput_f32_10khz, ifftFlag, doBitReverse);


/* Process the data through the Complex Magnitude Module for

calculating the magnitude at each bin */

arm_cmplx_mag_f32(testInput_f32_10khz, testOutput, fftSize);


/* Calculates maxValue and returns corresponding BIN value */

arm_max_f32(testOutput, fftSize, &maxValue, &testIndex);


if (testIndex != refIndex)

{

status = ARM_MATH_TEST_FAILURE;

}


/* ----------------------------------------------------------------------

** Loop here if the signals fail the PASS check.

** This denotes a test failure

** ------------------------------------------------------------------- */


if ( status != ARM_MATH_SUCCESS)

{

while (1);

}


while (1); /* main function does not return */

}