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/*
* Mark's Third Echo Canceller
*
* Copyright (C) 2003, Digium, Inc.
*
* This program is free software and may be used
* and distributed under the terms of the GNU General Public
* License, incorporated herein by reference.
*
* Dedicated to the crew of the Columbia, STS-107 for their
* bravery and courageous sacrifice for science.
*
*/
#ifndef _MARK3_ECHO_H
#define _MARK3_ECHO_H
#ifdef __KERNEL__
#include <linux/kernel.h>
#include <linux/slab.h>
#define MALLOC(a) kmalloc((a), GFP_KERNEL)
#define FREE(a) kfree(a)
#else
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#define MALLOC(a) malloc(a)
#define FREE(a) free(a)
#endif
/* Features */
/*
* DO_BACKUP -- Backup coefficients, and revert in the presense of double talk to try to prevent
* them from diverging during the ramp-up before the DTD kicks in
*/
/* #define DO_BACKUP */
#define STEP_SHIFT 2 /* Convergence rate higher = slower / better (as a shift) */
#define SIGMA_REF_PWR 655 /* Keep denominator from being 0 */
#define MIN_TX_ENERGY 256 /* Must have at least this much reference */
#define MIN_RX_ENERGY 32 /* Must have at least this much receive energy */
#define MAX_ATTENUATION_SHIFT 6 /* Maximum amount of loss we care about */
#define MAX_BETA 1024
#define SUPPR_SHIFT 4 /* Amount of loss at which we suppress audio */
#define HANG_TIME 600 /* Hangover time */
#define NTAPS 256 /* Number of echo can taps */
#define BACKUP 256 /* Backup every this number of samples */
#define POWER_OFFSET 5 /* Shift power by this amount to be sure we don't overflow the
reference power. Higher = less likely to overflow, lower = more accurage */
#include "arith.h"
typedef struct {
short buf[NTAPS * 2];
short max;
int maxexp;
} cbuf_s;
typedef struct {
short a_s[NTAPS]; /* Coefficients in shorts */
int a_i[NTAPS]; /* Coefficients in ints*/
#ifdef DO_BACKUP
int b_i[NTAPS]; /* Coefficients (backup1) */
int c_i[NTAPS]; /* Coefficients (backup2) */
#endif
cbuf_s ref; /* Reference excitation */
cbuf_s sig; /* Signal (echo + near end + noise) */
cbuf_s e; /* Error */
int refpwr; /* Reference power */
int taps; /* Number of taps */
int tappwr; /* Power of taps */
int hcntr; /* Hangtime counter */
int pos; /* Position in curcular buffers */
int backup; /* Backup timer */
} echo_can_state_t;
static inline void echo_can_free(echo_can_state_t *ec)
{
FREE(ec);
}
static inline void buf_add(cbuf_s *b, short sample, int pos, int taps)
{
/* Store and keep track of maxima */
int x;
b->buf[pos] = sample;
b->buf[pos + taps] = sample;
if (sample > b->max) {
b->max = sample;
b->maxexp = taps;
} else {
b->maxexp--;
if (!b->maxexp) {
b->max = 0;
for (x=0;x<taps;x++)
if (b->max < abs(b->buf[pos + x])) {
b->max = abs(b->buf[pos + x]);
b->maxexp = x + 1;
}
}
}
}
static inline short echo_can_update(echo_can_state_t *ec, short ref, short sig)
{
int x;
short u;
int refpwr;
int beta; /* Factor */
int se; /* Simulated echo */
#ifdef DO_BACKUP
if (!ec->backup) {
/* Backup coefficients periodically */
ec->backup = BACKUP;
memcpy(ec->c_i,ec->b_i,sizeof(ec->c_i));
memcpy(ec->b_i,ec->a_i,sizeof(ec->b_i));
} else
ec->backup--;
#endif
/* Remove old samples from reference power calculation */
ec->refpwr -= ((ec->ref.buf[ec->pos] * ec->ref.buf[ec->pos]) >> POWER_OFFSET);
/* Store signal and reference */
buf_add(&ec->ref, ref, ec->pos, ec->taps);
buf_add(&ec->sig, sig, ec->pos, ec->taps);
/* Add new reference power */
ec->refpwr += ((ec->ref.buf[ec->pos] * ec->ref.buf[ec->pos]) >> POWER_OFFSET);
/* Calculate simulated echo */
se = CONVOLVE2(ec->a_s, ec->ref.buf + ec->pos, ec->taps);
se >>= 15;
u = sig - se;
if (ec->hcntr)
ec->hcntr--;
/* Store error */
buf_add(&ec->e, sig, ec->pos, ec->taps);
if ((ec->ref.max > MIN_TX_ENERGY) &&
(ec->sig.max > MIN_RX_ENERGY) &&
(ec->e.max > (ec->ref.max >> MAX_ATTENUATION_SHIFT))) {
/* We have sufficient energy */
if (ec->sig.max < (ec->ref.max >> 1)) {
/* No double talk */
if (!ec->hcntr) {
refpwr = ec->refpwr >> (16 - POWER_OFFSET);
if (refpwr < SIGMA_REF_PWR)
refpwr = SIGMA_REF_PWR;
beta = (u << 16) / refpwr;
beta >>= STEP_SHIFT;
if (beta > MAX_BETA)
beta = MAX_BETA;
if (beta < -MAX_BETA)
beta = -MAX_BETA;
/* Update coefficients */
for (x=0;x<ec->taps;x++) {
ec->a_i[x] += beta * ec->ref.buf[ec->pos + x];
ec->a_s[x] = ec->a_i[x] >> 16;
}
}
} else {
#ifdef DO_BACKUP
if (!ec->hcntr) {
/* Our double talk detector is turning on for the first time. Revert
our coefficients, since we're probably well into the double talk by now */
memcpy(ec->a_i, ec->c_i, sizeof(ec->a_i));
for (x=0;x<ec->taps;x++) {
ec->a_s[x] = ec->a_i[x] >> 16;
}
}
#endif
/* Reset hang-time counter, and prevent backups */
ec->hcntr = HANG_TIME;
#ifdef DO_BACKUP
ec->backup = BACKUP;
#endif
}
}
#ifndef NO_ECHO__SUPPRESSOR
if (ec->e.max < (ec->ref.max >> SUPPR_SHIFT)) {
/* Suppress residual echo */
u *= u;
u >>= 16;
}
#endif
ec->pos--;
if (ec->pos < 0)
ec->pos = ec->taps-1;
return u;
}
static inline echo_can_state_t *echo_can_create(int taps, int adaption_mode)
{
echo_can_state_t *ec;
int x;
taps = NTAPS;
ec = MALLOC(sizeof(echo_can_state_t));
if (ec) {
memset(ec, 0, sizeof(echo_can_state_t));
ec->taps = taps;
ec->pos = ec->taps-1;
for (x=0;x<31;x++) {
if ((1 << x) >= ec->taps) {
ec->tappwr = x;
break;
}
}
}
return ec;
}
static inline int echo_can_traintap(echo_can_state_t *ec, int pos, short val)
{
/* Reset hang counter to avoid adjustments after
initial forced training */
ec->hcntr = ec->taps << 1;
if (pos >= ec->taps)
return 1;
ec->a_i[pos] = val << 17;
ec->a_s[pos] = val << 1;
if (++pos >= ec->taps)
return 1;
return 0;
}
#endif
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