DSP Applications and Student Projects - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 359

. . . N=256,16kHz rate,align x&w,... see Examples in Chapter 6
#include <rtdx.h>
short input_buffer[N] = {0}; //store input samples(same as x)

float output_buffer[N] = {0}; //store magnitude FFT

short buffer_count=0;
short nFlag=1; //when to begin the FFT

short i, j;
RTDX_CreateOutputChannel(ochan); //output channel C6x->PC transfer

interrupt void c_int11() //ISR

{
input_buffer[buffer_count] = input_sample(); //input -->buffer
output_sample(input_buffer[buffer_count++]); //loop
if(buffer_count >= N)
{ //if more than N pts, begin FFT

buffer_count = 0; //reset buffer_count

nFlag = 0; //flag to signal completion

for(i = 0; i < N; i++)
{
x[2*i]=(float)input_buffer[i]; //real component of input
x[2*i+1] = 0;

//imaginary component of input

}
}
}
void main(void)
{
. . . //generate twiddle constants and digit reversal index
comm_intr(); //init DSK
while(!RTDX_isOutputEnabled(&ochan));//wait for PC to enable RTDX
while(1)

//infinite loop

{
while(nFlag); //wait to finish accum samples

nFlag = 1;
cfftr4_dif(x, w, N); //call radix-4 FFT function
digit_reverse((double *)x, IIndex, JIndex, count);
for(j = 0; j < N; j++)
output_buffer[j]=(float)sqrt(x[2*j]*x[2*j]+x[2*j+1]*x[2*j+1]);
RTDX_write(&ochan,output_buffer,sizeof(output_buffer));//Send DSK>PC
};
}

( a )

( b )

FIGURE 10.10. ( a ) C program to implement radix-4 FFT and illustrate RTDX with Visual
C ++ , using MATLAB for FFT and plotting ( rtdx_vc_FFTr4.c ); ( b ) message when the

VC ++ application file is executed.