Fast Fourier Transform - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 238

#include "DSK6713_AIC23.h" //codec-DSK support file
Uint32 fs=DSK6713_AIC23_FREQ_8KHZ;//set sampling rate
#include <math.h>
#include "coeffs.h" //time domain FIR coefficients
#define PI 3.14159265358979
#define PTS 256 //number of points for FFT
#define SQRT_PTS 16 //used in twiddle factor calc.
#define RADIX 2 //passed to TI FFT routines
#define DELTA (2*PI)/PTS
typedef struct Complex_tag {float real, imag;} COMPLEX ;
#pragma DATA_ALIGN(W, sizeof(COMPLEX))
#pragma DATA_ALIGN(samples, sizeof(COMPLEX))
#pragma DATA_ALIGN(h, sizeof(COMPLEX))
COMPLEX W[PTS/RADIX] ; //twiddle factor array
COMPLEX samples[PTS]; //processing buffer
COMPLEX h[PTS]; //FIR filter coefficients
short buffercount = 0; //buffer count for iobuffer samples
float iobuffer[PTS/2]; //primary input/output buffer
float overlap[PTS/2]; //intermediate result buffer
short i; //index variable
short flag = 0; //set to indicate iobuffer full
float a, b; //variables used in complex multiply
short NUMCOEFFS = sizeof(coeffs)/sizeof(float);
short iTwid[SQRT_PTS] ; //PTS/2 + 1 > sqrt(PTS)

interrupt void c_int11(void) //ISR
{
output_sample((short)(iobuffer[buffercount]));
iobuffer[buffercount++] = (float)((short)input_sample());
if (buffercount >= PTS/2) //for overlap-add method iobuffer
{ //is half size of FFT used
buffercount = 0;
flag = 1;
}
}

main()
{ //set up array of twiddle factors
digitrev_index(iTwid, PTS/RADIX, RADIX);
for(i = 0 ; i < PTS/RADIX ; i++)
{
W[i].real = cos(DELTA*i);
W[i].imag = sin(DELTA*i);
}
bitrev(W, iTwid, PTS/RADIX); //bit reverse order W
for (i = 0 ; i<PTS ; i++) //initialise PTS element
{ //of COMPLEX to hold real-valued
h[i].real = 0.0; //time domain FIR filter coefficients
h[i].imag = 0.0;
}
for (i = 0 ; i < NUMCOEFFS ; i++)
{ //read FIR filter coeffs
h[i].real = coeffs[i]; //NUMCOEFFS should be less than PTS/2
}
cfftr2_dit(h,W,PTS); //transform filter coeffs

FIGURE 6.22. Fast convolution program using overlap-add with TI's floating-point FFT
functions ( fastconvo.c ).