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1 /*
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2 * SpanDSP - a series of DSP components for telephony
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3 *
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4 * modem_connect_tones.c - Generation and detection of tones
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5 * associated with modems calling and answering calls.
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6 *
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7 * Written by Steve Underwood <steveu@coppice.org>
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8 *
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9 * Copyright (C) 2006 Steve Underwood
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10 *
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11 * All rights reserved.
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12 *
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13 * This program is free software; you can redistribute it and/or modify
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14 * it under the terms of the GNU General Public License version 2, as
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15 * published by the Free Software Foundation.
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16 *
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17 * This program is distributed in the hope that it will be useful,
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18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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20 * GNU General Public License for more details.
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21 *
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22 * You should have received a copy of the GNU General Public License
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23 * along with this program; if not, write to the Free Software
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24 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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25 *
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26 * $Id: modem_connect_tones.h,v 1.4 2006/10/24 13:45:28 steveu Exp $
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27 */
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28
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29 /*! \file */
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30
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31 #if !defined(_MODEM_CONNECT_TONES_H_)
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32 #define _MODEM_CONNECT_TONES_H_
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33
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34 /*! \page modem_connect_tones_page Echo cancellor disable tone detection
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35
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36 \section modem_connect_tones_page_sec_1 What does it do?
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37 Some telephony terminal equipment, such as modems, require a channel which is as
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38 clear as possible. They use their own echo cancellation. If the network is also
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39 performing echo cancellation the two cancellors can end of squabbling about the
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40 nature of the channel, with bad results. A special tone is defined which should
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41 cause the network to disable any echo cancellation processes.
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42
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43 \section modem_connect_tones_page_sec_2 How does it work?
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44 A sharp notch filter is implemented as a single bi-quad section. The presence of
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45 the 2100Hz disable tone is detected by comparing the notched filtered energy
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46 with the unfiltered energy. If the notch filtered energy is much lower than the
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47 unfiltered energy, then a large proportion of the energy must be at the notch
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48 frequency. This type of detector may seem less intuitive than using a narrow
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49 bandpass filter to isolate the energy at the notch freqency. However, a sharp
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50 bandpass implemented as an IIR filter rings badly, The reciprocal notch filter
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51 is very well behaved.
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52 */
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53
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54 enum
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55 {
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56 MODEM_CONNECT_TONES_FAX_CNG,
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57 MODEM_CONNECT_TONES_FAX_CED,
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58 MODEM_CONNECT_TONES_EC_DISABLE,
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59 /*! \brief The version of EC disable with some 15Hz AM content, as in V.8 */
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60 MODEM_CONNECT_TONES_EC_DISABLE_MOD,
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61 };
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62
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63 /*!
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64 Modem connect tones generator descriptor. This defines the state
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65 of a single working instance of the tone generator.
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66 */
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67 typedef struct
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68 {
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69 int tone_type;
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70
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71 tone_gen_state_t tone_tx;
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72 uint32_t tone_phase;
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73 int32_t tone_phase_rate;
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74 int level;
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75 /*! \brief Countdown to the next phase hop */
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76 int hop_timer;
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77 uint32_t mod_phase;
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78 int32_t mod_phase_rate;
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79 int mod_level;
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80 } modem_connect_tones_tx_state_t;
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81
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82 /*!
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83 Modem connect tones receiver descriptor. This defines the state
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84 of a single working instance of the tone detector.
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85 */
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86 typedef struct
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87 {
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88 int tone_type;
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89 tone_report_func_t tone_callback;
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90 void *callback_data;
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91
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92 float z1;
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93 float z2;
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94 int notch_level;
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95 int channel_level;
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96 int tone_present;
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97 int tone_cycle_duration;
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98 int good_cycles;
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99 int hit;
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100 } modem_connect_tones_rx_state_t;
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101
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102 #ifdef __cplusplus
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103 extern "C" {
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104 #endif
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105
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106 /*! \brief Initialse an instance of the echo canceller disable tone generator.
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107 \param s The context.
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108 */
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109 modem_connect_tones_tx_state_t *modem_connect_tones_tx_init(modem_connect_tones_tx_state_t *s,
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110 int tone_type);
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111
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112 /*! \brief Generate a block of echo canceller disable tone samples.
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113 \param s The context.
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114 \param amp An array of signal samples.
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115 \param len The number of samples to generate.
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116 \return The number of samples generated.
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117 */
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118 int modem_connect_tones_tx(modem_connect_tones_tx_state_t *s,
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119 int16_t amp[],
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120 int len);
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121
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122 /*! \brief Process a block of samples through an instance of the modem_connect
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123 tones detector.
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124 \param s The context.
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125 \param amp An array of signal samples.
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126 \param len The number of samples in the array.
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127 \return The number of unprocessed samples.
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128 */
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129 int modem_connect_tones_rx(modem_connect_tones_rx_state_t *s,
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130 const int16_t amp[],
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131 int len);
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132
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133 /*! \brief Test if a modem_connect tone has been detected.
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134 \param s The context.
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135 \return TRUE if tone is detected, else FALSE.
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136 */
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137 int modem_connect_tones_rx_get(modem_connect_tones_rx_state_t *s);
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138
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139 /*! \brief Initialise an instance of the modem_connect tones detector.
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140 \param s The context.
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141 \param tone_type The type of connect tone being tested for.
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142 \param tone_callback An optional callback routine, used to report tones
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143 \param user_data An opaque pointer passed to the callback routine,
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144 \return A pointer to the context.
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145 */
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146 modem_connect_tones_rx_state_t *modem_connect_tones_rx_init(modem_connect_tones_rx_state_t *s,
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147 int tone_type,
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148 tone_report_func_t tone_callback,
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149 void *user_data);
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150
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151 #ifdef __cplusplus
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152 }
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153 #endif
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154
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155 #endif
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156 /*- End of file ------------------------------------------------------------*/
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