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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 * async.c - Asynchronous serial bit stream encoding and decoding
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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: async.c,v 1.6 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 #include <assert.h>
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38
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39 #include "spandsp/telephony.h"
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40 #include "spandsp/async.h"
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41
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42 void async_rx_init(async_rx_state_t *s,
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43 int data_bits,
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44 int parity,
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45 int stop_bits,
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46 int use_v14,
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47 put_byte_func_t put_byte,
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48 void *user_data)
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49 {
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50 s->data_bits = data_bits;
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51 s->parity = parity;
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52 s->stop_bits = stop_bits;
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53 s->use_v14 = use_v14;
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54
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55 s->put_byte = put_byte;
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56 s->user_data = user_data;
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57
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58 s->byte_in_progress = 0;
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59 s->bitpos = 0;
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60 s->parity_bit = 0;
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61
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62 s->parity_errors = 0;
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63 s->framing_errors = 0;
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64 }
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65 /*- End of function --------------------------------------------------------*/
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66
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67 void async_rx_put_bit(void *user_data, int bit)
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68 {
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69 async_rx_state_t *s;
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70
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71 s = (async_rx_state_t *) user_data;
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72 if (bit < 0)
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73 {
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74 /* Special conditions */
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75 switch (bit)
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76 {
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77 case PUTBIT_CARRIER_UP:
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78 case PUTBIT_CARRIER_DOWN:
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79 case PUTBIT_TRAINING_SUCCEEDED:
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80 case PUTBIT_TRAINING_FAILED:
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81 case PUTBIT_END_OF_DATA:
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82 s->put_byte(s->user_data, bit);
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83 s->bitpos = 0;
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84 s->byte_in_progress = 0;
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85 break;
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86 default:
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87 //printf("Eh!\n");
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88 break;
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89 }
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90 return;
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91 }
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92 if (s->bitpos == 0)
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93 {
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94 /* Search for the start bit */
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95 s->bitpos += (bit ^ 1);
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96 s->parity_bit = 0;
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97 s->byte_in_progress = 0;
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98 }
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99 else if (s->bitpos <= s->data_bits)
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100 {
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101 s->byte_in_progress = (s->byte_in_progress >> 1) | (bit << 7);
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102 s->parity_bit ^= bit;
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103 s->bitpos++;
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104 }
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105 else if (s->parity && s->bitpos == s->data_bits + 1)
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106 {
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107 if (s->parity == ASYNC_PARITY_ODD)
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108 s->parity_bit ^= 1;
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109
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110 if (s->parity_bit != bit)
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111 s->parity_errors++;
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112 s->bitpos++;
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113 }
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114 else
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115 {
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116 /* Stop bit */
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117 if (bit == 1)
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118 {
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119 /* Align the received value */
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120 if (s->data_bits < 8)
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121 s->byte_in_progress >>= (8 - s->data_bits);
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122 s->put_byte(s->user_data, s->byte_in_progress);
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123 s->bitpos = 0;
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124 }
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125 else if (s->use_v14)
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126 {
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127 /* This is actually the start bit for the next character, and
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128 the stop bit has been dropped from the stream. This is the
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129 rate adaption specified in V.14 */
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130 /* Align the received value */
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131 if (s->data_bits < 8)
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132 s->byte_in_progress >>= (8 - s->data_bits);
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133 s->put_byte(s->user_data, s->byte_in_progress);
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134 s->bitpos = 1;
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135 s->parity_bit = 0;
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136 s->byte_in_progress = 0;
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137 }
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138 else
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139 {
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140 s->framing_errors++;
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141 s->bitpos = 0;
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142 }
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143 }
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144 }
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145 /*- End of function --------------------------------------------------------*/
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146
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147 void async_tx_init(async_tx_state_t *s,
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148 int data_bits,
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149 int parity,
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150 int stop_bits,
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151 int use_v14,
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152 get_byte_func_t get_byte,
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153 void *user_data)
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154 {
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155 /* We have a use_v14 parameter for completeness, but right now V.14 only
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156 applies to the receive side. We are unlikely to have an application where
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157 flow control does not exist, so V.14 stuffing is not needed. */
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158 s->data_bits = data_bits;
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159 s->parity = parity;
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160 s->stop_bits = stop_bits;
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161 if (parity != ASYNC_PARITY_NONE)
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162 s->stop_bits++;
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163
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164 s->get_byte = get_byte;
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165 s->user_data = user_data;
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166
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167 s->byte_in_progress = 0;
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168 s->bitpos = 0;
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169 s->parity_bit = 0;
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170 }
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171 /*- End of function --------------------------------------------------------*/
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172
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173 int async_tx_get_bit(void *user_data)
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174 {
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175 async_tx_state_t *s;
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176 int bit;
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177
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178 s = (async_tx_state_t *) user_data;
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179 if (s->bitpos == 0)
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180 {
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181 if ((s->byte_in_progress = s->get_byte(s->user_data)) < 0)
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182 {
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183 /* No more data */
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184 bit = PUTBIT_END_OF_DATA;
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185 }
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186 else
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187 {
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188 /* Start bit */
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189 bit = 0;
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190 s->parity_bit = 0;
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191 s->bitpos++;
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192 }
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193 }
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194 else if (s->bitpos <= s->data_bits)
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195 {
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196 bit = s->byte_in_progress & 1;
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197 s->byte_in_progress >>= 1;
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198 s->parity_bit ^= bit;
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199 s->bitpos++;
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200 }
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201 else if (s->parity && s->bitpos == s->data_bits + 1)
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202 {
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203 if (s->parity == ASYNC_PARITY_ODD)
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204 s->parity_bit ^= 1;
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205 bit = s->parity_bit;
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206 s->bitpos++;
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207 }
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208 else
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209 {
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210 /* Stop bit(s) */
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211 bit = 1;
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212 if (++s->bitpos > s->data_bits + s->stop_bits)
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213 s->bitpos = 0;
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214 }
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215 return bit;
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216 }
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217 /*- End of function --------------------------------------------------------*/
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218 /*- End of file ------------------------------------------------------------*/
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