cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
Log | Files | Refs | README | LICENSE | sfeed.txt

dsp_ecdis.h (2909B)

      1/* SPDX-License-Identifier: GPL-2.0-or-later */
      2/*
      3 * SpanDSP - a series of DSP components for telephony
      4 *
      5 * ec_disable_detector.h - A detector which should eventually meet the
      6 *                         G.164/G.165 requirements for detecting the
      7 *                         2100Hz echo cancellor disable tone.
      8 *
      9 * Written by Steve Underwood <steveu@coppice.org>
     10 *
     11 * Copyright (C) 2001 Steve Underwood
     12 *
     13 * All rights reserved.
     14 */
     15
     16#include "dsp_biquad.h"
     17
     18struct ec_disable_detector_state {
     19	struct biquad2_state notch;
     20	int notch_level;
     21	int channel_level;
     22	int tone_present;
     23	int tone_cycle_duration;
     24	int good_cycles;
     25	int hit;
     26};
     27
     28
     29#define FALSE 0
     30#define TRUE (!FALSE)
     31
     32static inline void
     33echo_can_disable_detector_init(struct ec_disable_detector_state *det)
     34{
     35	/* Elliptic notch */
     36	/* This is actually centred at 2095Hz, but gets the balance we want, due
     37	   to the asymmetric walls of the notch */
     38	biquad2_init(&det->notch,
     39		     (int32_t)(-0.7600000 * 32768.0),
     40		     (int32_t)(-0.1183852 * 32768.0),
     41		     (int32_t)(-0.5104039 * 32768.0),
     42		     (int32_t)(0.1567596 * 32768.0),
     43		     (int32_t)(1.0000000 * 32768.0));
     44
     45	det->channel_level = 0;
     46	det->notch_level = 0;
     47	det->tone_present = FALSE;
     48	det->tone_cycle_duration = 0;
     49	det->good_cycles = 0;
     50	det->hit = 0;
     51}
     52/*- End of function --------------------------------------------------------*/
     53
     54static inline int
     55echo_can_disable_detector_update(struct ec_disable_detector_state *det,
     56				 int16_t amp)
     57{
     58	int16_t notched;
     59
     60	notched = biquad2(&det->notch, amp);
     61	/* Estimate the overall energy in the channel, and the energy in
     62	   the notch (i.e. overall channel energy - tone energy => noise).
     63	   Use abs instead of multiply for speed (is it really faster?).
     64	   Damp the overall energy a little more for a stable result.
     65	   Damp the notch energy a little less, so we don't damp out the
     66	   blip every time the phase reverses */
     67	det->channel_level += ((abs(amp) - det->channel_level) >> 5);
     68	det->notch_level += ((abs(notched) - det->notch_level) >> 4);
     69	if (det->channel_level > 280) {
     70		/* There is adequate energy in the channel.
     71		   Is it mostly at 2100Hz? */
     72		if (det->notch_level * 6 < det->channel_level) {
     73			/* The notch says yes, so we have the tone. */
     74			if (!det->tone_present) {
     75				/* Do we get a kick every 450+-25ms? */
     76				if (det->tone_cycle_duration >= 425 * 8
     77				    && det->tone_cycle_duration <= 475 * 8) {
     78					det->good_cycles++;
     79					if (det->good_cycles > 2)
     80						det->hit = TRUE;
     81				}
     82				det->tone_cycle_duration = 0;
     83			}
     84			det->tone_present = TRUE;
     85		} else
     86			det->tone_present = FALSE;
     87		det->tone_cycle_duration++;
     88	} else {
     89		det->tone_present = FALSE;
     90		det->tone_cycle_duration = 0;
     91		det->good_cycles = 0;
     92	}
     93	return det->hit;
     94}
     95/*- End of function --------------------------------------------------------*/
     96/*- End of file ------------------------------------------------------------*/