fskmodem_int.c

Go to the documentation of this file.

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2005, Digium, Inc.
 *
 * Mark Spencer <[email protected]>
 *
 * Includes code and algorithms from the Zapata library.
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief FSK Modulator/Demodulator
 *
 * \author Mark Spencer <[email protected]>
 *
 * \arg Includes code and algorithms from the Zapata library.
 *
 */

/*** MODULEINFO
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include "asterisk/fskmodem.h"

#define NBW 2
#define BWLIST {75,800}
#define  NF 6
#define  FLIST {1400,1800,1200,2200,1300,2100}

#define STATE_SEARCH_STARTBIT 0
#define STATE_SEARCH_STARTBIT2   1
#define STATE_SEARCH_STARTBIT3   2
#define STATE_GET_BYTE        3

static inline int iget_sample(short **buffer, int *len)
{
   int retval;
   retval = (int) **buffer;
   (*buffer)++;
   (*len)--;
   return retval;
}

#define IGET_SAMPLE iget_sample(&buffer, len)
/*! \brief Coefficients for input filters
 * Coefficients table, generated by program "mkfilter"
 * mkfilter is part of the zapatatelephony.org distribution
 * Format: coef[IDX_FREC][IDX_BW][IDX_COEF]
 * IDX_COEF = 0   => 1/GAIN
 * IDX_COEF = 1-6 => Coefficientes y[n]
*/
static double coef_in[NF][NBW][8]={
   {  { 1.8229206611e-04,-7.8997325866e-01,2.2401819940e+00,-4.6751353581e+00,5.5080745712e+00,-5.0571565772e+00,2.6215820004e+00,0.0000000000e+00,
   },  { 9.8532175289e-02,-5.6297236492e-02,3.3146713415e-01,-9.2239200436e-01,1.4844365184e+00,-2.0183258642e+00,2.0074154497e+00,0.0000000000e+00,
   },  },  {  { 1.8229206610e-04,-7.8997325866e-01,7.7191410839e-01,-2.8075643964e+00,1.6948618347e+00,-3.0367273700e+00,9.0333559408e-01,0.0000000000e+00,
   },  { 9.8531161839e-02,-5.6297236492e-02,1.1421579050e-01,-4.8122536483e-01,4.0121072432e-01,-7.4834487567e-01,6.9170822332e-01,0.0000000000e+00,
   },  },  {  { 1.8229206611e-04,-7.8997325866e-01,2.9003821430e+00,-6.1082779024e+00,7.7169345751e+00,-6.6075999680e+00,3.3941838836e+00,0.0000000000e+00,
   },  { 9.8539686961e-02,-5.6297236492e-02,4.2915323820e-01,-1.2609358633e+00,2.2399213250e+00,-2.9928879142e+00,2.5990173742e+00,0.0000000000e+00,
   },  },  {  { 1.8229206610e-04,-7.8997325866e-01,-7.7191410839e-01,-2.8075643964e+00,-1.6948618347e+00,-3.0367273700e+00,-9.0333559408e-01,0.0000000000e+00,
   },  { 9.8531161839e-02,-5.6297236492e-02,-1.1421579050e-01,-4.8122536483e-01,-4.0121072432e-01,-7.4834487567e-01,-6.9170822332e-01,0.0000000000e+00,
   },  },  {  { 1.8229206611e-04,-7.8997325866e-01,2.5782298908e+00,-5.3629717478e+00,6.5890882172e+00,-5.8012914776e+00,3.0171839130e+00,0.0000000000e+00,
   },  { 9.8534230718e-02,-5.6297236492e-02,3.8148618075e-01,-1.0848760410e+00,1.8441165168e+00,-2.4860666655e+00,2.3103384142e+00,0.0000000000e+00,
   },  },  {  { 1.8229206610e-04,-7.8997325866e-01,-3.8715051001e-01,-2.6192408538e+00,-8.3977994034e-01,-2.8329897913e+00,-4.5306444352e-01,0.0000000000e+00,
   },  { 9.8531160936e-02,-5.6297236492e-02,-5.7284484199e-02,-4.3673866734e-01,-1.9564766257e-01,-6.2028156584e-01,-3.4692356122e-01,0.0000000000e+00,
   },  },
};

/*! \brief Coefficients for output filter
 * Coefficients table, generated by program "mkfilter"
 * Format: coef[IDX_BW][IDX_COEF]
 * IDX_COEF = 0   => 1/GAIN
 * IDX_COEF = 1-6 => Coefficientes y[n]
*/
static double coef_out[NBW][8]={
   { 1.3868644653e-08,-6.3283665042e-01,4.0895057217e+00,-1.1020074592e+01,1.5850766191e+01,-1.2835109292e+01,5.5477477340e+00,0.0000000000e+00,
   },  { 3.1262119724e-03,-7.8390522307e-03,8.5209627801e-02,-4.0804129163e-01,1.1157139955e+00,-1.8767603680e+00,1.8916395224e+00,0.0000000000e+00
   },
};

/*! Integer Pass Band demodulator filter  */
static inline int ibpdfilter(struct filter_struct * fs, int in)
{
   int i,j;
   int s;
   int64_t s_interim;

   /* integer filter */
   s =  in * fs->icoefs[0];
   fs->ixv[(fs->ip + 6) & 7] = s;

   s =      (fs->ixv[fs->ip]           + fs->ixv[(fs->ip + 6) & 7]) +
      6  * (fs->ixv[(fs->ip + 1) & 7] + fs->ixv[(fs->ip + 5) & 7]) +
      15 * (fs->ixv[(fs->ip + 2) & 7] + fs->ixv[(fs->ip + 4) & 7]) +
      20 *  fs->ixv[(fs->ip + 3) & 7];

   for (i = 1, j = fs->ip; i < 7; i++, j++) {
      /* Promote operation to 64 bit to prevent overflow that occurred in 32 bit) */
      s_interim = (int64_t)(fs->iyv[j & 7]) *
            (int64_t)(fs->icoefs[i]) /
            (int64_t)(1024);
      s += (int) s_interim;
   }
   fs->iyv[j & 7] = s;
   fs->ip++;
   fs->ip &= 7;
   return s;
}

/*! Integer Band Pass filter */
static inline int ibpfilter(struct filter_struct * fs, int in)
{
   int i, j;
   int s;
   int64_t s_interim;

   /* integer filter */
   s =  in * fs->icoefs[0] / 256;
   fs->ixv[(fs->ip + 6) & 7] = s;

   s = (fs->ixv[(fs->ip + 6) & 7] - fs->ixv[fs->ip])
      + 3 * (fs->ixv[(fs->ip + 2) & 7] - fs->ixv[(fs->ip + 4) & 7]);

   for (i = 1, j = fs->ip; i < 7; i++, j++) {
      s_interim = (int64_t)(fs->iyv[j & 7]) *
            (int64_t)(fs->icoefs[i]) /
            (int64_t)(256);
      s += (int) s_interim;
   }
   fs->iyv[j & 7] = s;
   fs->ip++;
   fs->ip &= 7;
   return s;
}

static inline int idemodulator(fsk_data *fskd, int *retval, int x)
{
   int is, im, id;
   int ilin2;

   is = ibpfilter(&fskd->space_filter, x);
   im = ibpfilter(&fskd->mark_filter, x);

   ilin2 = ((im * im) - (is * is)) / (256 * 256);

   id = ibpdfilter(&fskd->demod_filter, ilin2);

   *retval = id;
   return 0;
}

static int get_bit_raw(fsk_data *fskd, short *buffer, int *len)
{
   /* This function implements a DPLL to synchronize with the bits */
   int f;

   int ix;
   /* PLL coeffs are set up in callerid_new */
   for (f = 0;;) {
      if (idemodulator(fskd, &ix, IGET_SAMPLE)) return(-1);
      if ((ix * fskd->xi0) < 0) { /* Transicion */
         if (!f) {
            if (fskd->icont < (fskd->pllispb2)) {
               fskd->icont += fskd->pllids;
            } else {
               fskd->icont -= fskd->pllids;
            }
            f = 1;
         }
      }
      fskd->xi0 = ix;
      fskd->icont += 32;
      if (fskd->icont > fskd->pllispb) {
         fskd->icont -= fskd->pllispb;
         break;
      }
   }
   f = (ix > 0) ? 0x80 : 0;
   return f;
}

int fskmodem_init(fsk_data *fskd)
{
   int i;

   fskd->space_filter.ip  = 0;
   fskd->mark_filter.ip   = 0;
   fskd->demod_filter.ip  = 0;

   for ( i = 0 ; i < 7 ; i++ ) {
      fskd->space_filter.icoefs[i] =
         coef_in[fskd->f_space_idx][fskd->bw][i] * 256;
      fskd->space_filter.ixv[i] = 0;;
      fskd->space_filter.iyv[i] = 0;;

      fskd->mark_filter.icoefs[i] =
         coef_in[fskd->f_mark_idx][fskd->bw][i] * 256;
      fskd->mark_filter.ixv[i] = 0;;
      fskd->mark_filter.iyv[i] = 0;;

      fskd->demod_filter.icoefs[i] =
         coef_out[fskd->bw][i] * 1024;
      fskd->demod_filter.ixv[i] = 0;;
      fskd->demod_filter.iyv[i] = 0;;
   }
   return 0;
}

int fsk_serial(fsk_data *fskd, short *buffer, int *len, int *outbyte)
{
   int a;
   int i, j, n1, r;
   int samples = 0;
   int olen;
   int beginlen = *len;
   int beginlenx;

   switch (fskd->state) {
      /* Pick up where we left off */
   case STATE_SEARCH_STARTBIT2:
      goto search_startbit2;
   case STATE_SEARCH_STARTBIT3:
      goto search_startbit3;
   case STATE_GET_BYTE:
      goto getbyte;
   }
   /* We await for start bit  */
   do {
      /* this was jesus's nice, reasonable, working (at least with RTTY) code
      to look for the beginning of the start bit. Unfortunately, since TTY/TDD's
      just start sending a start bit with nothing preceding it at the beginning
      of a transmission (what a LOSING design), we cant do it this elegantly */
      /* NOT USED
            if (demodulator(zap,&x1))
               return -1;
            for(;;) {
               if (demodulator(zap,&x2))
                  return -1;
               if (x1>0 && x2<0) break;
               x1=x2;
            }
      */
      /* this is now the imprecise, losing, but functional code to detect the
      beginning of a start bit in the TDD sceanario. It just looks for sufficient
      level to maybe, perhaps, guess, maybe that its maybe the beginning of
      a start bit, perhaps. This whole thing stinks! */
      beginlenx = beginlen; /* just to avoid unused war warnings */
      if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
         return -1;
      samples++;
      for(;;) {
search_startbit2:
         if (*len <= 0) {
            fskd->state = STATE_SEARCH_STARTBIT2;
            return 0;
         }
         samples++;
         if (idemodulator(fskd, &fskd->xi2, IGET_SAMPLE))
            return -1;
#if 0
         printf("xi2 = %d ", fskd->xi2);
#endif
         if (fskd->xi2 < 512) {
            break;
         }
      }
search_startbit3:
      /* We await for 0.5 bits before using DPLL */
      i = fskd->ispb / 2;
      if (*len < i) {
         fskd->state = STATE_SEARCH_STARTBIT3;
         return 0;
      }
      for (; i > 0; i--) {
         if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
            return(-1);
#if 0
         printf("xi1 = %d ", fskd->xi1);
#endif
         samples++;
      }

      /* x1 must be negative (start bit confirmation) */

   } while (fskd->xi1 > 0);
   fskd->state = STATE_GET_BYTE;

getbyte:

   /* Need at least 80 samples (for 1200) or
      1320 (for 45.5) to be sure we'll have a byte */
   if (fskd->nbit < 8) {
      if (*len < 1320)
         return 0;
   } else {
      if (*len < 80)
         return 0;
   }

   /* Now we read the data bits */
   j = fskd->nbit;
   for (a = n1 = 0; j; j--) {
      olen = *len;
      i = get_bit_raw(fskd, buffer, len);
      buffer += (olen - *len);
      if (i == -1)
         return -1;
      if (i)
         n1++;
      a >>= 1;
      a |= i;
   }
   j = 8 - fskd->nbit;
   a >>= j;

   /* We read parity bit (if exists) and check parity */
   if (fskd->parity) {
      olen = *len;
      i = get_bit_raw(fskd, buffer, len);
      buffer += (olen - *len);
      if (i == -1)
         return -1;
      if (i)
         n1++;
      if (fskd->parity == 1) {   /* parity=1 (even) */
         if (n1 & 1)
            a |= 0x100;       /* error */
      } else {             /* parity=2 (odd) */
         if (!(n1 & 1))
            a |= 0x100;       /* error */
      }
   }

   /* We read STOP bits. All of them must be 1 */

   for (j = fskd->instop; j; j--) {
      r = get_bit_raw(fskd, buffer, len);
      if (r == -1)
         return -1;
      if (!r)
         a |= 0x200;
   }

   /* And finally we return
    * Bit 8 : Parity error
    * Bit 9 : Framming error
   */

   *outbyte = a;
   fskd->state = STATE_SEARCH_STARTBIT;
   return 1;
}