ezdsp5535 source code for plotting fft spectrum on oled display

Hi all,

I have found the calculate_FFT() function which also displays the result on the OLED display of the ezdsp5535.

This has been added to my project on the ezdsp5535 which turns it into a USB Audio Class 2 stereo playback device with explicit rate feedback, and with automatic switching of sampling freq among 44.1/48/88.2/96khz at 24 bits.  Currently it only works with a Linux host (and a modified version for Mac OSX host).  Windows ASIO driver pending.

The source code of my whole project is in github  (NOTE:  this is a git repo,  NOT an http link.  You CANNOT click on it.)::

git://github.com/alexlee188/C5535.git

I have attached the binary bootimg.bin which you can test by copying into the root directory of a microSD card for your ezdsp5535.

The relevant code fragment for calculate_FFT() is copied below for easy reference:

/*****************************************************************************/
/* calculate_power() */
/*---------------------------------------------------------------------------*/
/* */
/* Parameter 1: Real term a. */
/* Parameter 2: Immaginary term jb. */
/* */
/* RETURNS: a*a + b*b. Result will always be positive. */
/* */
/*****************************************************************************/

int calculate_power (int a, int b)
{

return ( (int) ( ( (long)a * a + (long) b * b) >> 11) );
}

/*****************************************************************************/
/* calculate_FFT() */
/*---------------------------------------------------------------------------*/
/* */
/* Parameter 1: Latest audio input (real value). */
/* Parameter 2: size of FFT e.g. 128, 512 and 1024 elements. */
/* */
/* RETURNS: None. */
/* */
/*****************************************************************************/

void calculate_FFT(int *input, int size)
{
int i, j;
Uint16 out_sel;

for (i=0; i<size; i++)
{
bufferFFT[i*2] = input[i]; /* Store as a real value */
bufferFFT[i*2+1] = 0; /* Store with an imaginary value of 0 */
}

/* Perform complex FFT using N real and N imaginary values */

#if 1
cfft (&bufferFFT[0], size, SCALE);
cbrev(&bufferFFT[0], &bufferFFT[0], size);
out_sel = 1;
#else
hwafft_br((Int32 *)bufferFFT, (Int32 *)bufferScrach, 256);
out_sel = hwafft_256pts((Int32 *)bufferScrach, (Int32 *)bufferFFT, 0, 1);
#endif

// construct the bargraph
for ( j = 0 ; j < 128 ; j ++)
{
// display first 96 bins out of 128 bins (256/2)
if (out_sel)
display_buffer[j] = calculate_power((int) bufferFFT[2*j], (int)bufferFFT[2*j+1])+8;
else
display_buffer[j] = calculate_power((int) bufferScrach[2*j], (int)bufferScrach[2*j+1])+8;
}

// display the bargraph
oled_display_bargraph( &display_buffer[0]);
}

The bootimg.bin binary for the microSD card can be downloaded:

https://code.google.com/p/sdr-widget/downloads/detail?name=bootimg.bin&can=2&q=

Alex