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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
#define ECHO_CAN_FP
#ifdef __KERNEL__
#include <linux/kernel.h>
#include <linux/slab.h>
#define MALLOC(a) kmalloc((a), GFP_KERNEL)
#define FREE(a) kfree(a)
#include <math.h>
#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
/*
* Define COEFF_BACKUP for experimental coefficient backup code
*/
#define STEP_SIZE 0.4 /* Convergence rate */
#define SIGMA_P 0.01 /* Minimum adjustment */
#define SIGMA_REF_PWR 0.01 /* Keep denominator from being 0 */
#define MIN_TX_ENERGY 256.0/32767.0 /* Must have at least this much reference */
#define MIN_RX_ENERGY 32.0/32767.0 /* Must have at least this much receive energy */
#define MAX_ATTENUATION 64.0 /* Maximum amount of loss we care about */
#define MAX_BETA 0.1
#define SUPPR_ATTENUATION 16.0 /* 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 */
typedef struct {
float buf[NTAPS * 2];
float max;
int maxexp;
} cbuf_f;
typedef struct {
float a[NTAPS]; /* Coefficients */
#ifdef COEFF_BACKUP
float b[NTAPS]; /* Coefficients */
float c[NTAPS]; /* Coefficients */
int backup; /* Backup timer */
#endif
cbuf_f ref; /* Reference excitation */
cbuf_f sig; /* Signal (echo + near end + noise) */
cbuf_f e; /* Error */
float refpwr; /* Reference power */
int taps; /* Number of taps */
int hcntr; /* Hangtime counter */
int pos; /* Position in curcular buffers */
} echo_can_state_t;
static inline void echo_can_free(echo_can_state_t *ec)
{
FREE(ec);
}
static inline void buf_add(cbuf_f *b, float 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 < fabs(b->buf[pos + x])) {
b->max = fabs(b->buf[pos + x]);
b->maxexp = x + 1;
}
}
}
}
static inline short echo_can_update(echo_can_state_t *ec, short iref, short isig)
{
int x;
float ref;
float sig;
float u;
float refpwr;
float beta; /* Factor */
float se; /* Simulated echo */
/* Convert to floats about 1.0 */
ref = (((float)iref)/32767.0);
sig = (((float)isig)/32767.0);
#if 0
printf("start: %d, finish: %d\n", ec->start, ec->finish);
#endif
#ifdef COEFF_BACKUP
if (!ec->backup) {
/* Backup coefficients periodically */
ec->backup = BACKUP;
memcpy(ec->c,ec->b,sizeof(ec->c));
memcpy(ec->b,ec->a,sizeof(ec->b));
} else
ec->backup--;
#endif
/* Remove old samples from reference power calculation */
ec->refpwr -= (ec->ref.buf[ec->pos] * ec->ref.buf[ec->pos]);
/* 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]);
/* Calculate simulated echo */
se = 0.0;
for (x=0;x<ec->taps;x++)
se += ec->a[x] * ec->ref.buf[ec->pos + x];
#if 0
if (!(ec->pos2++ % 1024)) {
printk("sig: %d, se: %d\n", (int)(32768.0 * sig), (int)(32768.0 * se));
}
#endif
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 * MAX_ATTENUATION > ec->ref.max)) {
/* We have sufficient energy */
if (ec->sig.max * 2.0 < ec->ref.max) {
/* No double talk */
if (!ec->hcntr) {
if (ec->refpwr < SIGMA_REF_PWR)
refpwr = SIGMA_REF_PWR;
else
refpwr = ec->refpwr;
beta = STEP_SIZE * u / refpwr;
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[x] += beta * ec->ref.buf[ec->pos + x];
}
}
} else {
#ifdef COEFF_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, ec->c, sizeof(ec->a));
}
ec->backup = BACKUP;
#endif
/* Reset hang-time counter, and prevent backups */
ec->hcntr = HANG_TIME;
}
}
#ifndef NO_ECHO_SUPPRESSOR
if (ec->e.max * SUPPR_ATTENUATION < ec->ref.max) {
/* Suppress residual echo */
u *= u;
}
#endif
ec->pos--;
if (ec->pos < 0)
ec->pos = ec->taps-1;
u *= 32767.0;
if (u < -32768.0)
u = -32768.0;
if (u > 32767.0)
u = 32767.0;
return (short)(u);
}
static inline echo_can_state_t *echo_can_create(int taps, int adaption_mode)
{
echo_can_state_t *ec;
taps = NTAPS;
ec = MALLOC(sizeof(echo_can_state_t));
if (ec) {
printk("Allocating MEC3 canceller (%d)\n", taps);
memset(ec, 0, sizeof(echo_can_state_t));
ec->taps = taps;
if (ec->taps > NTAPS)
ec->taps = NTAPS;
ec->pos = ec->taps-1;
}
return ec;
}
#endif
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