Adaptive Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 271

// AdaptIDFIR.c Adaptive FIR for system ID of an FIR

#include "DSK6713_AIC23.h" //codec-DSK support file
Uint32 fs=DSK6713_AIC23_FREQ_8KHZ; //set sampling rate
#include "bp55.cof" //fixed FIR filter coefficients
#include "noise_gen.h" //support noise generation file
#define beta 1E-14 //rate of convergence
#define WLENGTH 60 //# of coefffor adaptive FIR
float w[WLENGTH+1]; //buffer coeff for adaptive FIR
int dly_adapt[WLENGTH+1]; //buffer samples of adaptive FIR
int dly_fix[N+1]; //buffer samples of fixed FIR
short out_type = 1; //output for adaptive/fixed FIR
int fb; //feedback variable
shift_reg sreg; //shift register

int prand(void) //pseudo-random sequence {-1,1}

{
int prnseq;
if(sreg.bt.b0) prnseq = -8000; //scaled negative noise level
else prnseq = 8000; //scaled positive noise level
fb =(sreg.bt.b0)^(sreg.bt.b1); //XOR bits 0,1
fb^=(sreg.bt.b11)^(sreg.bt.b13); //with bits 11,13 -> fb
sreg.regval<<=1;
sreg.bt.b0=fb;

//close feedback path

return prnseq; //return noise sequence

}

interrupt void c_int11() //ISR
{
int i;
int fir_out = 0; //init output of fixed FIR
int adaptfir_out = 0; //init output of adapt FIR
float E; //error=diff of fixed/adapt out
dly_fix[0] = prand(); //input noise to fixed FIR
dly_adapt[0]=dly_fix[0]; //as well as to adaptive FIR
for (i = N-1; i>= 0; i--)
{
fir_out +=(h[i]*dly_fix[i]); //fixed FIR filter output
dly_fix[i+1] = dly_fix[i]; //update samples of fixed FIR
}
for (i = 0; i < WLENGTH; i++)
adaptfir_out +=(w[i]*dly_adapt[i]); //adaptive FIR filter output
E = fir_out - adaptfir_out; //error signal
for (i = WLENGTH-1; i >= 0; i--)
{
w[i] = w[i]+(beta*E*dly_adapt[i]); //update weights of adaptive FIR
dly_adapt[i+1] = dly_adapt[i]; //update samples of adaptive FIR
}
if (out_type == 1) //slider position for adapt FIR
output_sample((short)adaptfir_out); //output of adaptive FIR filter
else if (out_type == 2) //slider position for fixed FIR
output_sample((short)fir_out); //output of fixed FIR filter
return;
}

FIGURE 7.19. Program to implement an adaptive FIR filter that models (identifies) a fixed
FIR filter ( adaptIDFIR.c ).