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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 * v27ter_rx.h - ITU V.27ter modem receive part
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5 *
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6 * Written by Steve Underwood <steveu@coppice.org>
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7 *
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8 * Copyright (C) 2003 Steve Underwood
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9 *
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10 * All rights reserved.
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11 *
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12 * This program is free software; you can redistribute it and/or modify
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13 * it under the terms of the GNU General Public License version 2, as
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14 * published by the Free Software Foundation.
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15 *
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16 * This program is distributed in the hope that it will be useful,
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17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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19 * GNU General Public License for more details.
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20 *
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21 * You should have received a copy of the GNU General Public License
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22 * along with this program; if not, write to the Free Software
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23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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24 *
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25 * $Id: v27ter_rx.h,v 1.34 2006/10/24 13:45:28 steveu Exp $
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26 */
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27
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28 /*! \file */
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29
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30 #if !defined(_V27TER_RX_H_)
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31 #define _V27TER_RX_H_
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32
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33 /*! \page v27ter_rx_page The V.27ter receiver
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34
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35 \section v27ter_rx_page_sec_1 What does it do?
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36 The V.27ter receiver implements the receive side of a V.27ter modem. This can operate
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37 at data rates of 4800 and 2400 bits/s. The audio input is a stream of 16 bit samples,
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38 at 8000 samples/second. The transmit and receive side of V.27ter modems operate
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39 independantly. V.27ter is mostly used for FAX transmission, where it provides the
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40 standard 4800 bits/s rate (the 2400 bits/s mode is not used for FAX).
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41
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42 \section v27ter_rx_page_sec_2 How does it work?
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43 V.27ter defines two modes of operation. One uses 8-PSK at 1600 baud, giving 4800bps.
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44 The other uses 4-PSK at 1200 baud, giving 2400bps. A training sequence is specified
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45 at the start of transmission, which makes the design of a V.27ter receiver relatively
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46 straightforward.
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47 */
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48
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49 /* Target length for the equalizer is about 43 taps for 4800bps and 32 taps for 2400bps
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50 to deal with the worst stuff in V.56bis. */
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51 #define V27TER_EQUALIZER_PRE_LEN 15 /* this much before the real event */
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52 #define V27TER_EQUALIZER_POST_LEN 15 /* this much after the real event */
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53 #define V27TER_EQUALIZER_MASK 63 /* one less than a power of 2 >= (V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN) */
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54
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55 #define V27TER_RX_4800_FILTER_STEPS 27
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56 #define V27TER_RX_2400_FILTER_STEPS 27
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57
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58 #if V27TER_RX_4800_FILTER_STEPS > V27TER_RX_2400_FILTER_STEPS
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59 #define V27TER_RX_FILTER_STEPS V27TER_RX_4800_FILTER_STEPS
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60 #else
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61 #define V27TER_RX_FILTER_STEPS V27TER_RX_2400_FILTER_STEPS
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62 #endif
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63
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64 /*!
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65 V.27ter modem receive side descriptor. This defines the working state for a
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66 single instance of a V.27ter modem receiver.
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67 */
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68 typedef struct
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69 {
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70 /*! \brief The bit rate of the modem. Valid values are 2400 and 4800. */
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71 int bit_rate;
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72 /*! \brief The callback function used to put each bit received. */
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73 put_bit_func_t put_bit;
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74 /*! \brief A user specified opaque pointer passed to the put_bit routine. */
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75 void *user_data;
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76 /*! \brief A callback function which may be enabled to report every symbol's
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77 constellation position. */
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78 qam_report_handler_t *qam_report;
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79 /*! \brief A user specified opaque pointer passed to the qam_report callback
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80 routine. */
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81 void *qam_user_data;
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82
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83 /*! \brief The route raised cosine (RRC) pulse shaping filter buffer. */
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84 float rrc_filter[2*V27TER_RX_FILTER_STEPS];
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85 /*! \brief Current offset into the RRC pulse shaping filter buffer. */
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86 int rrc_filter_step;
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87
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88 /*! \brief The register for the training and data scrambler. */
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89 unsigned int scramble_reg;
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90 /*! \brief A counter for the number of consecutive bits of repeating pattern through
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91 the scrambler. */
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92 int scrambler_pattern_count;
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93 int in_training;
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94 int training_bc;
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95 int training_count;
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96 float training_error;
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97 int carrier_present;
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98 int16_t last_sample;
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99 /*! \brief TRUE if the previous trained values are to be reused. */
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100 int old_train;
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101
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102 /*! \brief The current phase of the carrier (i.e. the DDS parameter). */
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103 uint32_t carrier_phase;
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104 /*! \brief The update rate for the phase of the carrier (i.e. the DDS increment). */
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105 int32_t carrier_phase_rate;
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106 /*! \brief The carrier update rate saved for reuse when using short training. */
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107 int32_t carrier_phase_rate_save;
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108 float carrier_track_p;
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109 float carrier_track_i;
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110
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111 power_meter_t power;
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112 int32_t carrier_on_power;
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113 int32_t carrier_off_power;
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114 float agc_scaling;
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115 float agc_scaling_save;
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116
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117 int constellation_state;
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118
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119 float eq_delta;
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120 /*! \brief The adaptive equalizer coefficients */
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121 complexf_t eq_coeff[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
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122 complexf_t eq_coeff_save[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
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123 complexf_t eq_buf[V27TER_EQUALIZER_MASK + 1];
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124 /*! \brief Current offset into equalizer buffer. */
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125 int eq_step;
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126 int eq_put_step;
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127 int eq_skip;
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128
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129 /*! \brief Integration variable for damping the Gardner algorithm tests. */
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130 int gardner_integrate;
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131 /*! \brief Current step size of Gardner algorithm integration. */
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132 int gardner_step;
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133 /*! \brief The total symbol timing correction since the carrier came up.
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134 This is only for performance analysis purposes. */
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135 int total_baud_timing_correction;
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136 /*! \brief The current fractional phase of the baud timing. */
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137 int baud_phase;
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138
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139 /*! \brief Starting phase angles for the coarse carrier aquisition step. */
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140 int32_t start_angles[2];
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141 /*! \brief History list of phase angles for the coarse carrier aquisition step. */
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142 int32_t angles[16];
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143 /*! \brief Error and flow logging control */
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144 logging_state_t logging;
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145 } v27ter_rx_state_t;
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146
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147 #ifdef __cplusplus
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148 extern "C" {
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149 #endif
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150
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151 /*! Initialise a V.27ter modem receive context.
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152 \brief Initialise a V.27ter modem receive context.
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153 \param s The modem context.
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154 \param rate The bit rate of the modem. Valid values are 2400 and 4800.
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155 \param put_bit The callback routine used to put the received data.
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156 \param user_data An opaque pointer passed to the put_bit routine.
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157 \return A pointer to the modem context, or NULL if there was a problem. */
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158 v27ter_rx_state_t *v27ter_rx_init(v27ter_rx_state_t *s, int rate, put_bit_func_t put_bit, void *user_data);
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159
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160 /*! Reinitialise an existing V.27ter modem receive context.
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161 \brief Reinitialise an existing V.27ter modem receive context.
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162 \param s The modem context.
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163 \param rate The bit rate of the modem. Valid values are 2400 and 4800.
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164 \param old_train TRUE if a previous trained values are to be reused.
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165 \return 0 for OK, -1 for bad parameter */
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166 int v27ter_rx_restart(v27ter_rx_state_t *s, int rate, int old_train);
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167
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168 /*! Release a V.27ter modem receive context.
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169 \brief Release a V.27ter modem receive context.
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170 \param s The modem context.
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171 \return 0 for OK */
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172 int v27ter_rx_release(v27ter_rx_state_t *s);
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173
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174 /*! Change the put_bit function associated with a V.27ter modem receive context.
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175 \brief Change the put_bit function associated with a V.27ter modem receive context.
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176 \param s The modem context.
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177 \param put_bit The callback routine used to handle received bits.
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178 \param user_data An opaque pointer. */
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179 void v27ter_rx_set_put_bit(v27ter_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
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180
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181 /*! Process a block of received V.27ter modem audio samples.
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182 \brief Process a block of received V.27ter modem audio samples.
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183 \param s The modem context.
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184 \param amp The audio sample buffer.
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185 \param len The number of samples in the buffer.
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186 \return The number of samples unprocessed.
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187 */
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188 int v27ter_rx(v27ter_rx_state_t *s, const int16_t amp[], int len);
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189
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190 /*! Get a snapshot of the current equalizer coefficients.
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191 \brief Get a snapshot of the current equalizer coefficients.
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192 \param coeffs The vector of complex coefficients.
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193 \return The number of coefficients in the vector. */
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194 int v27ter_rx_equalizer_state(v27ter_rx_state_t *s, complexf_t **coeffs);
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195
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196 /*! Get the current received carrier frequency.
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197 \param s The modem context.
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198 \return The frequency, in Hertz. */
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199 float v27ter_rx_carrier_frequency(v27ter_rx_state_t *s);
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200
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201 /*! Get the current symbol timing correction since startup.
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202 \param s The modem context.
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203 \return The correction. */
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204 float v27ter_rx_symbol_timing_correction(v27ter_rx_state_t *s);
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205
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206 /*! Get a current received signal power.
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207 \param s The modem context.
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208 \return The signal power, in dBm0. */
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209 float v27ter_rx_signal_power(v27ter_rx_state_t *s);
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210
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211 /*! Set the power level at which the carrier detection will cut in
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212 \param s The modem context.
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213 \param cutoff The signal cutoff power, in dBm0. */
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214 void v27ter_rx_signal_cutoff(v27ter_rx_state_t *s, float cutoff);
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215
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216 /*! Set a handler routine to process QAM status reports
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217 \param s The modem context.
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218 \param handler The handler routine.
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219 \param user_data An opaque pointer passed to the handler routine. */
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220 void v27ter_rx_set_qam_report_handler(v27ter_rx_state_t *s, qam_report_handler_t *handler, void *user_data);
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221
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222 #ifdef __cplusplus
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223 }
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224 #endif
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225
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226 #endif
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227 /*- End of file ------------------------------------------------------------*/
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