How to use fft function in TMD320C6657 DSP

Kwon Seol

Now I'm trying to use DSP_16x16_fft function.

but it's some different with matlab fft function. that function was short type but in matlab fft function was double type.

So I make input for short type. But Output was different with matlab..

#include <stdint.h>
#include <math.h>
#include <ti/dsplib/dsplib.h>
#include "gen_twiddle_fft16x16.h"
#include <time.h>
#define N 256
#pragma DATA_ALIGN(x_16x16, 8);
int16_t x_16x16 [2*N];
#pragma DATA_ALIGN(y_16x16, 8);
int16_t y_16x16 [2*N];
#pragma DATA_ALIGN(w_16x16, 8);
int16_t w_16x16 [2*N];
#pragma DATA_ALIGN(x_sp, 8);
float x_sp [2*N];
#pragma DATA_ALIGN(y_sp, 8);
float y_sp [2*N];
#pragma DATA_ALIGN(w_sp, 8);
float w_sp [2*N];
unsigned char brev[64] = {
0x0, 0x20, 0x10, 0x30, 0x8, 0x28, 0x18, 0x38,
0x4, 0x24, 0x14, 0x34, 0xc, 0x2c, 0x1c, 0x3c,
0x2, 0x22, 0x12, 0x32, 0xa, 0x2a, 0x1a, 0x3a,
0x6, 0x26, 0x16, 0x36, 0xe, 0x2e, 0x1e, 0x3e,
0x1, 0x21, 0x11, 0x31, 0x9, 0x29, 0x19, 0x39,
0x5, 0x25, 0x15, 0x35, 0xd, 0x2d, 0x1d, 0x3d,
0x3, 0x23, 0x13, 0x33, 0xb, 0x2b, 0x1b, 0x3b,
0x7, 0x27, 0x17, 0x37, 0xf, 0x2f, 0x1f, 0x3f
};
void generateInput () {
int32_t i, j;
for (i = 0; i < N; i++) {
x_16x16[2*i] = 1;
x_16x16[2*i + 1] = 1;
x_sp[2*i] = 1;
x_sp[2*i+1] = 1;
}
}
void gen_twiddle_fft_sp (float *w, int n)
{
int i, j, k;
const double PI = 3.141592654;

for (j = 1, k = 0; j <= n >> 2; j = j << 2)
{
for (i = 0; i < n >> 2; i += j)
{
#ifdef _LITTLE_ENDIAN
w[k] = (float) sin (2 * PI * i / n);
w[k + 1] = (float) cos (2 * PI * i / n);
w[k + 2] = (float) sin (4 * PI * i / n);
w[k + 3] = (float) cos (4 * PI * i / n);
w[k + 4] = (float) sin (6 * PI * i / n);
w[k + 5] = (float) cos (6 * PI * i / n);
#else
w[k] = (float) cos (2 * PI * i / n);
w[k + 1] = (float) -sin (2 * PI * i / n);
w[k + 2] = (float) cos (4 * PI * i / n);
w[k + 3] = (float) -sin (4 * PI * i / n);
w[k + 4] = (float) cos (6 * PI * i / n);
w[k + 5] = (float) -sin (6 * PI * i / n);
#endif
k += 6;
}
}
}

/*
The seperateRealImg function seperates the real and imaginary data
of the FFT output. This is needed so that the data can be plotted
using the CCS graph feature
*/

int16_t y_real_16x16 [N];
int16_t y_imag_16x16 [N];
int16_t x_real_16x16 [N];
int16_t x_imag_16x16 [N];
float y_real_sp [N];
float y_imag_sp [N];
float x_real_sp [N];
float x_imag_sp [N];

seperateInputRealImg () {
int32_t i, j;

for (i = 0, j = 0; j < N; i+=2, j++) {
x_real_16x16[j] = x_16x16[i];
x_imag_16x16[j] = x_16x16[i + 1];
}
}

seperateInputRealImgsp () {
int32_t i, j;

for (i = 0, j = 0; j < N; i+=2, j++) {
x_real_sp[j] = x_sp[i];
x_imag_sp[j] = x_sp[i + 1];
}
}

seperateRealImg () {
int32_t i, j;

for (i = 0, j = 0; j < N; i+=2, j++) {
y_real_16x16[j] = y_16x16[i];
y_imag_16x16[j] = y_16x16[i + 1];
}
}
seperateRealImgsp () {
int32_t i, j;

for (i = 0, j = 0; j < N; i+=2, j++) {
y_real_sp[j] = y_sp[i];
y_imag_sp[j] = y_sp[i + 1];
}
}

void main () {
/* Generate the input data */
generateInput ();
/* Genarate the various twiddle factors */
gen_twiddle_fft16x16(w_16x16, N);
gen_twiddle_fft_sp(w_sp, N);
seperateInputRealImg (x_16x16);
seperateInputRealImgsp (x_sp);
DSPF_sp_fftSPxSP(N, x_sp, w_sp, y_sp, brev, 2, 0, N);
/* Call the various FFT routines */
DSP_fft16x16(w_16x16, N, x_16x16, y_16x16);

/* Call the test code to seperate the real and imaginary data */
seperateRealImg (y_16x16);
seperateRealImgsp (y_sp);
}

follow photh is my input and output signal.

ccs output