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5
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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 * fsk.c - FSK modem transmit and receive parts
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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: fsk.c,v 1.27 2006/11/19 14:07:24 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 #ifdef HAVE_CONFIG_H
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31 #include <config.h>
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32 #endif
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33
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34 #include <inttypes.h>
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35 #include <stdlib.h>
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36 #include <string.h>
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37 #if defined(HAVE_TGMATH_H)
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38 #include <tgmath.h>
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39 #endif
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40 #if defined(HAVE_MATH_H)
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41 #include <math.h>
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42 #endif
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43 #include <assert.h>
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44
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45 #include "spandsp/telephony.h"
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46 #include "spandsp/complex.h"
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47 #include "spandsp/dds.h"
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48 #include "spandsp/power_meter.h"
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49 #include "spandsp/async.h"
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50 #include "spandsp/fsk.h"
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51
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52 fsk_spec_t preset_fsk_specs[] =
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53 {
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54 {
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55 "V21 ch 1",
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56 1080 + 100,
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57 1080 - 100,
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58 -14,
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59 -30,
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60 300
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61 },
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62 {
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63 "V21 ch 2",
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64 1750 + 100,
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65 1750 - 100,
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66 -14,
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67 -30,
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68 300
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69 },
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70 {
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71 "V23 ch 1",
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72 2100,
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73 1300,
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74 -14,
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75 -30,
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76 1200
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77 },
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78 {
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79 "V23 ch 2",
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80 450,
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81 390,
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82 -14,
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83 -30,
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84 75
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85 },
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86 {
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87 "Bell103 ch 1",
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88 2125 - 100,
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89 2125 + 100,
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90 -14,
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91 -30,
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92 300
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93 },
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94 {
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95 "Bell103 ch 2",
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96 1170 - 100,
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97 1170 + 100,
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98 -14,
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99 -30,
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100 300
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101 },
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102 {
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103 "Bell202",
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104 2200,
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105 1200,
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106 -14,
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107 -30,
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108 1200
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109 },
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110 {
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111 "Weitbrecht", /* Used for TDD (Telecomc Device for the Deaf) */
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112 1800,
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113 1400,
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114 -14,
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115 -30,
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116 45 /* Actually 45.45 */
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117 }
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118 };
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119
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120 fsk_tx_state_t *fsk_tx_init(fsk_tx_state_t *s,
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121 fsk_spec_t *spec,
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122 get_bit_func_t get_bit,
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123 void *user_data)
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124 {
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125 s->baud_rate = spec->baud_rate;
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126 s->get_bit = get_bit;
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127 s->user_data = user_data;
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128
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129 s->phase_rates[0] = dds_phase_rate((float) spec->freq_zero);
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130 s->phase_rates[1] = dds_phase_rate((float) spec->freq_one);
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131 s->scaling = dds_scaling_dbm0((float) spec->tx_level);
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132 /* Initialise fractional sample baud generation. */
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133 s->phase_acc = 0;
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134 s->baud_inc = (s->baud_rate*0x10000)/SAMPLE_RATE;
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135 s->baud_frac = 0;
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136 s->current_phase_rate = s->phase_rates[1];
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137
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138 s->shutdown = FALSE;
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139 return s;
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140 }
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141 /*- End of function --------------------------------------------------------*/
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142
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143 int fsk_tx(fsk_tx_state_t *s, int16_t *amp, int len)
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144 {
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145 int sample;
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146 int bit;
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147
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148 if (s->shutdown)
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149 return 0;
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150 /* Make the transitions between 0 and 1 phase coherent, but instantaneous
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151 jumps. There is currently no interpolation for bauds that end mid-sample.
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152 Mainstream users will not care. Some specialist users might have a problem
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153 with they, if they care about accurate transition timing. */
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154 for (sample = 0; sample < len; sample++)
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155 {
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156 if ((s->baud_frac += s->baud_inc) >= 0x10000)
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157 {
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158 s->baud_frac -= 0x10000;
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159 if ((bit = s->get_bit(s->user_data)) == PUTBIT_END_OF_DATA)
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160 {
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161 s->shutdown = TRUE;
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162 break;
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163 }
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164 s->current_phase_rate = s->phase_rates[bit & 1];
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165 }
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166 amp[sample] = dds_mod(&(s->phase_acc), s->current_phase_rate, s->scaling, 0);
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167 }
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168 return sample;
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169 }
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170 /*- End of function --------------------------------------------------------*/
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171
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172 void fsk_tx_power(fsk_tx_state_t *s, float power)
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173 {
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174 s->scaling = dds_scaling_dbm0(power);
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175 }
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176 /*- End of function --------------------------------------------------------*/
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177
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178 void fsk_tx_set_get_bit(fsk_tx_state_t *s, get_bit_func_t get_bit, void *user_data)
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179 {
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180 s->get_bit = get_bit;
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181 s->user_data = user_data;
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182 }
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183 /*- End of function --------------------------------------------------------*/
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184
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185 void fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff)
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186 {
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187 s->min_power = power_meter_level_dbm0(cutoff);
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188 }
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189 /*- End of function --------------------------------------------------------*/
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190
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191 float fsk_rx_signal_power(fsk_rx_state_t *s)
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192 {
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193 return power_meter_dbm0(&s->power);
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194 }
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195 /*- End of function --------------------------------------------------------*/
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196
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197 void fsk_rx_set_put_bit(fsk_rx_state_t *s, put_bit_func_t put_bit, void *user_data)
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198 {
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199 s->put_bit = put_bit;
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200 s->user_data = user_data;
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201 }
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202 /*- End of function --------------------------------------------------------*/
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203
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204 fsk_rx_state_t *fsk_rx_init(fsk_rx_state_t *s,
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205 fsk_spec_t *spec,
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206 int sync_mode,
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207 put_bit_func_t put_bit,
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208 void *user_data)
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209 {
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210 int chop;
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211
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212 memset(s, 0, sizeof(*s));
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213 s->baud_rate = spec->baud_rate;
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214 s->sync_mode = sync_mode;
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215 s->min_power = power_meter_level_dbm0((float) spec->min_level);
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216 s->put_bit = put_bit;
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217 s->user_data = user_data;
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218
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219 /* Detect by correlating against the tones we want, over a period
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220 of one baud. The correlation must be quadrature. */
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221
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222 /* First we need the quadrature tone generators to correlate
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223 against. */
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224 s->phase_rate[0] = dds_phase_rate((float) spec->freq_zero);
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225 s->phase_rate[1] = dds_phase_rate((float) spec->freq_one);
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226 s->phase_acc[0] = 0;
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227 s->phase_acc[1] = 0;
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228 s->last_sample = 0;
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229
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230 /* The correlation should be over one baud. */
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231 s->correlation_span = SAMPLE_RATE/spec->baud_rate;
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232 /* But limit it for very slow baud rates, so we do not overflow our
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233 buffer. */
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234 if (s->correlation_span > FSK_MAX_WINDOW_LEN)
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235 s->correlation_span = FSK_MAX_WINDOW_LEN;
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236
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237 /* We need to scale, to avoid overflow in the correlation. */
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238 s->scaling_shift = 0;
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239 chop = s->correlation_span;
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240 while (chop != 0)
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241 {
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242 s->scaling_shift++;
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243 chop >>= 1;
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244 }
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245
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246 /* Initialise the baud/bit rate tracking. */
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247 s->baud_inc = (s->baud_rate*0x10000)/SAMPLE_RATE;
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248 s->baud_pll = 0;
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249
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250 /* Initialise a power detector, so sense when a signal is present. */
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251 power_meter_init(&(s->power), 4);
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252 s->carrier_present = FALSE;
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253 return s;
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254 }
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255 /*- End of function --------------------------------------------------------*/
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256
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257 int fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len)
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258 {
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259 int buf_ptr;
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260 int baudstate;
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261 int sample;
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262 int j;
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263 int32_t dot;
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264 int32_t sum;
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265 int32_t power;
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266 icomplex_t ph;
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267
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268 buf_ptr = s->buf_ptr;
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269
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270 for (sample = 0; sample < len; sample++)
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271 {
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272 /* If there isn't much signal, don't demodulate - it will only produce
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273 useless junk results. */
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274 /* TODO: The carrier signal has no hysteresis! */
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275 power = power_meter_update(&(s->power), amp[sample] - s->last_sample);
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276 s->last_sample = amp[sample];
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277 if (power < s->min_power)
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278 {
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279 if (s->carrier_present)
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280 {
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281 s->put_bit(s->user_data, PUTBIT_CARRIER_DOWN);
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282 s->carrier_present = FALSE;
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283 }
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284 continue;
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285 }
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286 if (!s->carrier_present)
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287 {
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288 s->put_bit(s->user_data, PUTBIT_CARRIER_UP);
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289 s->carrier_present = TRUE;
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290 }
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291 /* Non-coherent FSK demodulation by correlation with the target tones
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292 over a one baud interval. The slow V.xx specs. are too open ended
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293 to allow anything fancier to be used. The dot products are calculated
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294 using a sliding window approach, so the compute load is not that great. */
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295 /* The *totally* asynchronous character to character behaviour of these
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296 modems, when carrying async. data, seems to force a sample by sample
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297 approach. */
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298 for (j = 0; j < 2; j++)
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299 {
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300 s->dot_i[j] -= s->window_i[j][buf_ptr];
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301 s->dot_q[j] -= s->window_q[j][buf_ptr];
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302
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303 ph = dds_complex(&(s->phase_acc[j]), s->phase_rate[j]);
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304 s->window_i[j][buf_ptr] = (ph.re*amp[sample]) >> s->scaling_shift;
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305 s->window_q[j][buf_ptr] = (ph.im*amp[sample]) >> s->scaling_shift;
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306
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307 s->dot_i[j] += s->window_i[j][buf_ptr];
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308 s->dot_q[j] += s->window_q[j][buf_ptr];
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309 }
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310 dot = s->dot_i[0] >> 15;
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311 sum = dot*dot;
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312 dot = s->dot_q[0] >> 15;
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313 sum += dot*dot;
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314 dot = s->dot_i[1] >> 15;
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315 sum -= dot*dot;
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316 dot = s->dot_q[1] >> 15;
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317 sum -= dot*dot;
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318 baudstate = (sum < 0);
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319
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320 if (s->lastbit != baudstate)
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321 {
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322 s->lastbit = baudstate;
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323 if (s->sync_mode)
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324 {
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325 /* For synchronous use (e.g. HDLC channels in FAX modems), nudge
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326 the baud phase gently, trying to keep it centred on the bauds. */
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327 if (s->baud_pll < 0x8000)
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328 s->baud_pll += (s->baud_inc >> 3);
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329 else
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330 s->baud_pll -= (s->baud_inc >> 3);
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331 }
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332 else
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333 {
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334 /* For async. operation, believe transitions completely, and
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335 sample appropriately. This allows instant start on the first
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336 transition. */
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337 /* We must now be about half way to a sampling point. We do not do
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338 any fractional sample estimation of the transitions, so this is
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339 the most accurate baud alignment we can do. */
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340 s->baud_pll = 0x8000;
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341 }
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342
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343 }
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344 if ((s->baud_pll += s->baud_inc) >= 0x10000)
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345 {
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346 /* We should be in the middle of a baud now, so report the current
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347 state as the next bit */
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348 s->baud_pll -= 0x10000;
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349 s->put_bit(s->user_data, baudstate);
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350 }
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351 if (++buf_ptr >= s->correlation_span)
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352 buf_ptr = 0;
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353 }
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354 s->buf_ptr = buf_ptr;
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355 return 0;
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356 }
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357 /*- End of function --------------------------------------------------------*/
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358 /*- End of file ------------------------------------------------------------*/
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