drivers/isdn/mISDN/dsp_ecdis.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * SpanDSP - a series of DSP components for telephony
 *
 * ec_disable_detector.h - A detector which should eventually meet the
 *                         G.164/G.165 requirements for detecting the
 *                         2100Hz echo cancellor disable tone.
 *
 * Written by Steve Underwood <steveu@coppice.org>
 *
 * Copyright (C) 2001 Steve Underwood
 *
 * All rights reserved.
 */

#include "dsp_biquad.h"

struct ec_disable_detector_state {
	struct biquad2_state notch;
	int notch_level;
	int channel_level;
	int tone_present;
	int tone_cycle_duration;
	int good_cycles;
	int hit;
};


#define FALSE 0
#define TRUE (!FALSE)

static inline void
echo_can_disable_detector_init(struct ec_disable_detector_state *det)
{
	/* Elliptic notch */
	/* This is actually centred at 2095Hz, but gets the balance we want, due
	   to the asymmetric walls of the notch */
	biquad2_init(&det->notch,
		     (int32_t)(-0.7600000 * 32768.0),
		     (int32_t)(-0.1183852 * 32768.0),
		     (int32_t)(-0.5104039 * 32768.0),
		     (int32_t)(0.1567596 * 32768.0),
		     (int32_t)(1.0000000 * 32768.0));

	det->channel_level = 0;
	det->notch_level = 0;
	det->tone_present = FALSE;
	det->tone_cycle_duration = 0;
	det->good_cycles = 0;
	det->hit = 0;
}
/*- End of function --------------------------------------------------------*/

static inline int
echo_can_disable_detector_update(struct ec_disable_detector_state *det,
				 int16_t amp)
{
	int16_t notched;

	notched = biquad2(&det->notch, amp);
	/* Estimate the overall energy in the channel, and the energy in
	   the notch (i.e. overall channel energy - tone energy => noise).
	   Use abs instead of multiply for speed (is it really faster?).
	   Damp the overall energy a little more for a stable result.
	   Damp the notch energy a little less, so we don't damp out the
	   blip every time the phase reverses */
	det->channel_level += ((abs(amp) - det->channel_level) >> 5);
	det->notch_level += ((abs(notched) - det->notch_level) >> 4);
	if (det->channel_level > 280) {
		/* There is adequate energy in the channel.
		   Is it mostly at 2100Hz? */
		if (det->notch_level * 6 < det->channel_level) {
			/* The notch says yes, so we have the tone. */
			if (!det->tone_present) {
				/* Do we get a kick every 450+-25ms? */
				if (det->tone_cycle_duration >= 425 * 8
				    && det->tone_cycle_duration <= 475 * 8) {
					det->good_cycles++;
					if (det->good_cycles > 2)
						det->hit = TRUE;
				}
				det->tone_cycle_duration = 0;
			}
			det->tone_present = TRUE;
		} else
			det->tone_present = FALSE;
		det->tone_cycle_duration++;
	} else {
		det->tone_present = FALSE;
		det->tone_cycle_duration = 0;
		det->good_cycles = 0;
	}
	return det->hit;
}
/*- End of function --------------------------------------------------------*/
/*- End of file ------------------------------------------------------------*/