www.pudn.com > SMV_Code.rar > agc.c
/*=========================================================================*/
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/*=========================================================================*/
/* */
/*-------------------------------------------------------------------*/
/*===================================================================*/
/* ..Includes. */
/*---------------------------------------------------------------------------*/
#include
#include
#include "basic_op40.h"
#include "basic_op.h"
#include "dtmf.h"
#include "tables.h"
/*===========================================================================*/
/* ..Defines. */
/*---------------------------------------------------------------------------*/
#define SQRT_ITERATIONS 16
/*===========================================================================*/
/* ..Functions. */
/*---------------------------------------------------------------------------*/
short sqrt_approx(long);
/*===========================================================================*/
/* ..Scales input data block to avoid overflow in goertzel filters. */
/*---------------------------------------------------------------------------*/
void agc (
DTMF_DETECTOR* D, /* (i) - pointer to detector structure */
short* data /* (i/o) - data buffer */
)
{
/* ..(local) variables..*/
register int j;
short *dinP;
short *doutP;
short gain_const;
short gain_lev;
short gain_amp;
short gain_scale;
long Lgain_lim;
long Lgain_power;
Acc accA;
/* ..execute..*/
/* Compute constants that depend on N (with rounding) */
/* (Use hardcoded integer values in final implementation!) */
Lgain_lim = (long) ((2147483648. * (1. / 64.) * (1. / (float) N)) + 0.5);
gain_const = (short) ((32768. * (sqrt (64. / (float) N))) + 0.5);
gain_lev = (short) ((32768. * (.5*sqrt(2.) / (float) N)) + 0.5);
dinP = data;
accA = 0;
for (j = 0; j < N; j++)
{
accA = L_mac40(accA, *dinP, *dinP);
dinP++;
}
accA =L_shr40(accA,6); /* A = A / 64 */
Lgain_power = accA ;
dinP = data;
doutP = data;
if (Lgain_power>Lgain_lim ) {
accA = L_mult(gain_const, sqrt_approx(Lgain_power));
accA=L_shr40(accA,16);
gain_amp = extract_l40( (accA));
gain_scale = divide_s(gain_lev,gain_amp);
/* scale the data by 'gain_scale' */
for (j = 0; j < N; j++)
{
accA = L_mult(gain_scale, (*dinP++));
accA= L_shr40(accA,16);
*doutP++ =extract_l40(accA);
}
}
return;
}
/* Fixed point square root approximation */
short sqrt_approx ( /* (o) - output: 0 <= y < 1.0 (Q15) */
long L_x /* (i) - input: 0 <= x < 1.0 (Q31) */
)
{
/* ..(local) variables..*/
register int j;
short y;
Acc accA;
Acc accB;
Acc accC;
/* ..execute..*/
accC = (0x40000000); /* delta = 0.5 */
y = 0x4000; /* y = 0.5 */
accA = L_mult(y,y);
accA = L_sub40(accA, L_x); /* (A) = yold*yold - x */
for (j=0; j 0) {
accB = L_sub40(accB, accC); /* (B) = yold - (1/2)*delta */
} else {
accB = L_add40(accB, accC); /* (B) = yold + (1/2)*delta */
}
accB=L_shr40(accB,16);
y = extract_l40(accB); /* (BH) --> ynew */
accA = L_mult(y,y);
accA = L_sub40(accA, L_x); /* (A) = yold*yold - x */
}
return y;
}