main/fskmodem.c

   1 /*
   2  * Asterisk -- An open source telephony toolkit.
   3  *
   4  * Copyright (C) 1999 - 2005, Digium, Inc.
   5  *
   6  * Mark Spencer <markster@digium.com>
   7  *
   8  * Includes code and algorithms from the Zapata library.
   9  *
  10  * See http://www.asterisk.org for more information about
  11  * the Asterisk project. Please do not directly contact
  12  * any of the maintainers of this project for assistance;
  13  * the project provides a web site, mailing lists and IRC
  14  * channels for your use.
  15  *
  16  * This program is free software, distributed under the terms of
  17  * the GNU General Public License Version 2. See the LICENSE file
  18  * at the top of the source tree.
  19  */
  20
  21 /*! \file
  22  *
  23  * \brief FSK Modulator/Demodulator
  24  *
  25  * \author Mark Spencer <markster@digium.com>
  26  *
  27  * \arg Includes code and algorithms from the Zapata library.
  28  *
  29  */
  30
  31 #include "asterisk.h"
  32
  33 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
  34
  35 #include "asterisk/fskmodem.h"
  36
  37 #define NBW     2
  38 #define BWLIST  {75,800}
  39 #define NF      6
  40 #define FLIST {1400,1800,1200,2200,1300,2100}
  41
  42 #define STATE_SEARCH_STARTBIT   0
  43 #define STATE_SEARCH_STARTBIT2  1
  44 #define STATE_SEARCH_STARTBIT3  2
  45 #define STATE_GET_BYTE                  3
  46
  47 static inline int iget_sample(short **buffer, int *len)
  48 {
  49         int retval;
  50         retval = (int) **buffer;
  51         (*buffer)++;
  52         (*len)--;
  53         return retval;
  54 }
  55
  56 #define IGET_SAMPLE iget_sample(&buffer, len)
  57 /*! \brief Coefficients for input filters
  58  * Coefficients table, generated by program "mkfilter"
  59  * mkfilter is part of the zapatatelephony.org distribution
  60  * Format: coef[IDX_FREC][IDX_BW][IDX_COEF]
  61  * IDX_COEF = 0 =>      1/GAIN
  62  * IDX_COEF = 1-6       =>      Coefficientes y[n]
  63 */
  64 static double coef_in[NF][NBW][8]={
  65         {  { 1.8229206611e-04,-7.8997325866e-01,2.2401819940e+00,-4.6751353581e+00,5.5080745712e+00,-5.0571565772e+00,2.6215820004e+00,0.0000000000e+00,
  66         },  { 9.8532175289e-02,-5.6297236492e-02,3.3146713415e-01,-9.2239200436e-01,1.4844365184e+00,-2.0183258642e+00,2.0074154497e+00,0.0000000000e+00,
  67         },  },  {  { 1.8229206610e-04,-7.8997325866e-01,7.7191410839e-01,-2.8075643964e+00,1.6948618347e+00,-3.0367273700e+00,9.0333559408e-01,0.0000000000e+00,
  68         },  { 9.8531161839e-02,-5.6297236492e-02,1.1421579050e-01,-4.8122536483e-01,4.0121072432e-01,-7.4834487567e-01,6.9170822332e-01,0.0000000000e+00,
  69         },  },  {  { 1.8229206611e-04,-7.8997325866e-01,2.9003821430e+00,-6.1082779024e+00,7.7169345751e+00,-6.6075999680e+00,3.3941838836e+00,0.0000000000e+00,
  70         },  { 9.8539686961e-02,-5.6297236492e-02,4.2915323820e-01,-1.2609358633e+00,2.2399213250e+00,-2.9928879142e+00,2.5990173742e+00,0.0000000000e+00,
  71         },  },  {  { 1.8229206610e-04,-7.8997325866e-01,-7.7191410839e-01,-2.8075643964e+00,-1.6948618347e+00,-3.0367273700e+00,-9.0333559408e-01,0.0000000000e+00,
  72         },  { 9.8531161839e-02,-5.6297236492e-02,-1.1421579050e-01,-4.8122536483e-01,-4.0121072432e-01,-7.4834487567e-01,-6.9170822332e-01,0.0000000000e+00,
  73         },  },  {  { 1.8229206611e-04,-7.8997325866e-01,2.5782298908e+00,-5.3629717478e+00,6.5890882172e+00,-5.8012914776e+00,3.0171839130e+00,0.0000000000e+00,
  74         },  { 9.8534230718e-02,-5.6297236492e-02,3.8148618075e-01,-1.0848760410e+00,1.8441165168e+00,-2.4860666655e+00,2.3103384142e+00,0.0000000000e+00,
  75         },  },  {  { 1.8229206610e-04,-7.8997325866e-01,-3.8715051001e-01,-2.6192408538e+00,-8.3977994034e-01,-2.8329897913e+00,-4.5306444352e-01,0.0000000000e+00,
  76         },  { 9.8531160936e-02,-5.6297236492e-02,-5.7284484199e-02,-4.3673866734e-01,-1.9564766257e-01,-6.2028156584e-01,-3.4692356122e-01,0.0000000000e+00,
  77         },  },
  78 };
  79
  80 /*! \brief Coefficients for output filter
  81  * Coefficients table, generated by program "mkfilter"
  82  * Format: coef[IDX_BW][IDX_COEF]
  83  * IDX_COEF = 0 =>      1/GAIN
  84  * IDX_COEF = 1-6       =>      Coefficientes y[n]
  85 */
  86 static double coef_out[NBW][8]={
  87         { 1.3868644653e-08,-6.3283665042e-01,4.0895057217e+00,-1.1020074592e+01,1.5850766191e+01,-1.2835109292e+01,5.5477477340e+00,0.0000000000e+00,
  88         },  { 3.1262119724e-03,-7.8390522307e-03,8.5209627801e-02,-4.0804129163e-01,1.1157139955e+00,-1.8767603680e+00,1.8916395224e+00,0.0000000000e+00
  89         },
  90 };
  91
  92 /*! Integer Pass Band demodulator filter  */
  93 static inline int ibpdfilter(struct filter_struct * fs, int in)
  94 {
  95         int i,j;
  96         int s;
  97         int64_t s_interim;
  98
  99         /* integer filter */
 100         s =  in * fs->icoefs[0];
 101         fs->ixv[(fs->ip + 6) & 7] = s;
 102
 103         s =      (fs->ixv[fs->ip]           + fs->ixv[(fs->ip + 6) & 7]) +
 104                 6  * (fs->ixv[(fs->ip + 1) & 7] + fs->ixv[(fs->ip + 5) & 7]) +
 105                 15 * (fs->ixv[(fs->ip + 2) & 7] + fs->ixv[(fs->ip + 4) & 7]) +
 106                 20 *  fs->ixv[(fs->ip + 3) & 7];
 107
 108         for (i = 1, j = fs->ip; i < 7; i++, j++) {
 109                 /* Promote operation to 64 bit to prevent overflow that occurred in 32 bit) */
 110                 s_interim = (int64_t)(fs->iyv[j & 7]) *
 111                                 (int64_t)(fs->icoefs[i]) /
 112                                 (int64_t)(1024);
 113                 s += (int) s_interim;
 114         }
 115         fs->iyv[j & 7] = s;
 116         fs->ip++;
 117         fs->ip &= 7;
 118         return s;
 119 }
 120
 121 /*! Integer Band Pass filter */
 122 static inline int ibpfilter(struct filter_struct * fs, int in)
 123 {
 124         int i, j;
 125         int s;
 126         int64_t s_interim;
 127
 128         /* integer filter */
 129         s =  in * fs->icoefs[0] / 256;
 130         fs->ixv[(fs->ip + 6) & 7] = s;
 131
 132         s = (fs->ixv[(fs->ip + 6) & 7] - fs->ixv[fs->ip])
 133                 + 3 * (fs->ixv[(fs->ip + 2) & 7] - fs->ixv[(fs->ip + 4) & 7]);
 134
 135         for (i = 1, j = fs->ip; i < 7; i++, j++) {
 136                 s_interim = (int64_t)(fs->iyv[j & 7]) *
 137                                 (int64_t)(fs->icoefs[i]) /
 138                                 (int64_t)(256);
 139                 s += (int) s_interim;
 140         }
 141         fs->iyv[j & 7] = s;
 142         fs->ip++;
 143         fs->ip &= 7;
 144         return s;
 145 }
 146
 147 static inline int idemodulator(fsk_data *fskd, int *retval, int x)
 148 {
 149         int is, im, id;
 150         int ilin2;
 151
 152         is = ibpfilter(&fskd->space_filter, x);
 153         im = ibpfilter(&fskd->mark_filter, x);
 154
 155         ilin2 = ((im * im) - (is * is)) / (256 * 256);
 156
 157         id = ibpdfilter(&fskd->demod_filter, ilin2);
 158
 159         *retval = id;
 160         return 0;
 161 }
 162
 163 static int get_bit_raw(fsk_data *fskd, short *buffer, int *len)
 164 {
 165         /* This function implements a DPLL to synchronize with the bits */
 166         int f;
 167
 168         int ix;
 169         /* PLL coeffs are set up in callerid_new */
 170         for (f = 0;;) {
 171                 if (idemodulator(fskd, &ix, IGET_SAMPLE)) return(-1);
 172                 if ((ix * fskd->xi0) < 0) { /* Transicion */
 173                         if (!f) {
 174                                 if (fskd->icont < (fskd->pllispb2)) {
 175                                         fskd->icont += fskd->pllids;
 176                                 } else {
 177                                         fskd->icont -= fskd->pllids;
 178                                 }
 179                                 f = 1;
 180                         }
 181                 }
 182                 fskd->xi0 = ix;
 183                 fskd->icont += 32;
 184                 if (fskd->icont > fskd->pllispb) {
 185                         fskd->icont -= fskd->pllispb;
 186                         break;
 187                 }
 188         }
 189         f = (ix > 0) ? 0x80 : 0;
 190         return f;
 191 }
 192
 193 int fskmodem_init(fsk_data *fskd)
 194 {
 195         int i;
 196
 197         fskd->space_filter.ip  = 0;
 198         fskd->mark_filter.ip   = 0;
 199         fskd->demod_filter.ip  = 0;
 200
 201         for ( i = 0 ; i < 7 ; i++ ) {
 202                 fskd->space_filter.icoefs[i] =
 203                         coef_in[fskd->f_space_idx][fskd->bw][i] * 256;
 204                 fskd->space_filter.ixv[i] = 0;;
 205                 fskd->space_filter.iyv[i] = 0;;
 206
 207                 fskd->mark_filter.icoefs[i] =
 208                         coef_in[fskd->f_mark_idx][fskd->bw][i] * 256;
 209                 fskd->mark_filter.ixv[i] = 0;;
 210                 fskd->mark_filter.iyv[i] = 0;;
 211
 212                 fskd->demod_filter.icoefs[i] =
 213                         coef_out[fskd->bw][i] * 1024;
 214                 fskd->demod_filter.ixv[i] = 0;;
 215                 fskd->demod_filter.iyv[i] = 0;;
 216         }
 217         return 0;
 218 }
 219
 220 int fsk_serial(fsk_data *fskd, short *buffer, int *len, int *outbyte)
 221 {
 222         int a;
 223         int i, j, n1, r;
 224         int samples = 0;
 225         int olen;
 226         int beginlen = *len;
 227         int beginlenx;
 228
 229         switch (fskd->state) {
 230                 /* Pick up where we left off */
 231         case STATE_SEARCH_STARTBIT2:
 232                 goto search_startbit2;
 233         case STATE_SEARCH_STARTBIT3:
 234                 goto search_startbit3;
 235         case STATE_GET_BYTE:
 236                 goto getbyte;
 237         }
 238         /* We await for start bit       */
 239         do {
 240                 /* this was jesus's nice, reasonable, working (at least with RTTY) code
 241                 to look for the beginning of the start bit. Unfortunately, since TTY/TDD's
 242                 just start sending a start bit with nothing preceding it at the beginning
 243                 of a transmission (what a LOSING design), we cant do it this elegantly */
 244                 /* NOT USED
 245                                 if (demodulator(zap,&x1))
 246                                         return -1;
 247                                 for(;;) {
 248                                         if (demodulator(zap,&x2))
 249                                                 return -1;
 250                                         if (x1>0 && x2<0) break;
 251                                         x1=x2;
 252                                 }
 253                 */
 254                 /* this is now the imprecise, losing, but functional code to detect the
 255                 beginning of a start bit in the TDD sceanario. It just looks for sufficient
 256                 level to maybe, perhaps, guess, maybe that its maybe the beginning of
 257                 a start bit, perhaps. This whole thing stinks! */
 258                 beginlenx = beginlen; /* just to avoid unused war warnings */
 259                 if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
 260                         return -1;
 261                 samples++;
 262                 for(;;) {
 263 search_startbit2:
 264                         if (*len <= 0) {
 265                                 fskd->state = STATE_SEARCH_STARTBIT2;
 266                                 return 0;
 267                         }
 268                         samples++;
 269                         if (idemodulator(fskd, &fskd->xi2, IGET_SAMPLE))
 270                                 return -1;
 271 #if 0
 272                         printf("xi2 = %d ", fskd->xi2);
 273 #endif
 274                         if (fskd->xi2 < 512) {
 275                                 break;
 276                         }
 277                 }
 278 search_startbit3:
 279                 /* We await for 0.5 bits before using DPLL */
 280                 i = fskd->ispb / 2;
 281                 if (*len < i) {
 282                         fskd->state = STATE_SEARCH_STARTBIT3;
 283                         return 0;
 284                 }
 285                 for (; i > 0; i--) {
 286                         if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
 287                                 return(-1);
 288 #if 0
 289                         printf("xi1 = %d ", fskd->xi1);
 290 #endif
 291                         samples++;
 292                 }
 293
 294                 /* x1 must be negative (start bit confirmation) */
 295
 296         } while (fskd->xi1 > 0);
 297         fskd->state = STATE_GET_BYTE;
 298
 299 getbyte:
 300
 301         /* Need at least 80 samples (for 1200) or
 302                 1320 (for 45.5) to be sure we'll have a byte */
 303         if (fskd->nbit < 8) {
 304                 if (*len < 1320)
 305                         return 0;
 306         } else {
 307                 if (*len < 80)
 308                         return 0;
 309         }
 310
 311         /* Now we read the data bits */
 312         j = fskd->nbit;
 313         for (a = n1 = 0; j; j--) {
 314                 olen = *len;
 315                 i = get_bit_raw(fskd, buffer, len);
 316                 buffer += (olen - *len);
 317                 if (i == -1)
 318                         return -1;
 319                 if (i)
 320                         n1++;
 321                 a >>= 1;
 322                 a |= i;
 323         }
 324         j = 8 - fskd->nbit;
 325         a >>= j;
 326
 327         /* We read parity bit (if exists) and check parity */
 328         if (fskd->parity) {
 329                 olen = *len;
 330                 i = get_bit_raw(fskd, buffer, len);
 331                 buffer += (olen - *len);
 332                 if (i == -1)
 333                         return -1;
 334                 if (i)
 335                         n1++;
 336                 if (fskd->parity == 1) {        /* parity=1 (even) */
 337                         if (n1 & 1)
 338                                 a |= 0x100;                     /* error */
 339                 } else {                                        /* parity=2 (odd) */
 340                         if (!(n1 & 1))
 341                                 a |= 0x100;                     /* error */
 342                 }
 343         }
 344
 345         /* We read STOP bits. All of them must be 1 */
 346
 347         for (j = fskd->instop; j; j--) {
 348                 r = get_bit_raw(fskd, buffer, len);
 349                 if (r == -1)
 350                         return -1;
 351                 if (!r)
 352                         a |= 0x200;
 353         }
 354
 355         /* And finally we return
 356          * Bit 8 : Parity error
 357          * Bit 9 : Framming error
 358         */
 359
 360         *outbyte = a;
 361         fskd->state = STATE_SEARCH_STARTBIT;
 362         return 1;
 363 }