Wed Oct 28 11:45:38 2009

Asterisk developer's documentation


fskmodem_int.c

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 1999 - 2005, Digium, Inc.
00005  *
00006  * Mark Spencer <markster@digium.com>
00007  * 
00008  * Includes code and algorithms from the Zapata library.
00009  *
00010  * See http://www.asterisk.org for more information about
00011  * the Asterisk project. Please do not directly contact
00012  * any of the maintainers of this project for assistance;
00013  * the project provides a web site, mailing lists and IRC
00014  * channels for your use.
00015  *
00016  * This program is free software, distributed under the terms of
00017  * the GNU General Public License Version 2. See the LICENSE file
00018  * at the top of the source tree.
00019  */
00020 
00021 /*! \file
00022  *
00023  * \brief FSK Modulator/Demodulator 
00024  *
00025  * \author Mark Spencer <markster@digium.com>
00026  *
00027  * \arg Includes code and algorithms from the Zapata library.
00028  *
00029  */
00030 
00031 #include "asterisk.h"
00032 
00033 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 132512 $")
00034 
00035 #include "asterisk/fskmodem.h"
00036 
00037 #define NBW 2
00038 #define BWLIST {75,800}
00039 #define  NF 6
00040 #define  FLIST {1400,1800,1200,2200,1300,2100}
00041 
00042 #define STATE_SEARCH_STARTBIT 0
00043 #define STATE_SEARCH_STARTBIT2   1
00044 #define STATE_SEARCH_STARTBIT3   2
00045 #define STATE_GET_BYTE        3
00046 
00047 static inline int iget_sample(short **buffer, int *len)
00048 {
00049    int retval;
00050    retval = (int) **buffer;
00051    (*buffer)++;
00052    (*len)--;
00053    return retval;
00054 }
00055 
00056 #define IGET_SAMPLE iget_sample(&buffer, len)
00057 /*! \brief Coefficients for input filters
00058  * Coefficients table, generated by program "mkfilter"   
00059  * mkfilter is part of the zapatatelephony.org distribution
00060  * Format: coef[IDX_FREC][IDX_BW][IDX_COEF]
00061  * IDX_COEF = 0   => 1/GAIN      
00062  * IDX_COEF = 1-6 => Coefficientes y[n]         
00063 */
00064 static double coef_in[NF][NBW][8]={
00065    {  { 1.8229206611e-04,-7.8997325866e-01,2.2401819940e+00,-4.6751353581e+00,5.5080745712e+00,-5.0571565772e+00,2.6215820004e+00,0.0000000000e+00,
00066    },  { 9.8532175289e-02,-5.6297236492e-02,3.3146713415e-01,-9.2239200436e-01,1.4844365184e+00,-2.0183258642e+00,2.0074154497e+00,0.0000000000e+00,
00067    },  },  {  { 1.8229206610e-04,-7.8997325866e-01,7.7191410839e-01,-2.8075643964e+00,1.6948618347e+00,-3.0367273700e+00,9.0333559408e-01,0.0000000000e+00,
00068    },  { 9.8531161839e-02,-5.6297236492e-02,1.1421579050e-01,-4.8122536483e-01,4.0121072432e-01,-7.4834487567e-01,6.9170822332e-01,0.0000000000e+00,
00069    },  },  {  { 1.8229206611e-04,-7.8997325866e-01,2.9003821430e+00,-6.1082779024e+00,7.7169345751e+00,-6.6075999680e+00,3.3941838836e+00,0.0000000000e+00,
00070    },  { 9.8539686961e-02,-5.6297236492e-02,4.2915323820e-01,-1.2609358633e+00,2.2399213250e+00,-2.9928879142e+00,2.5990173742e+00,0.0000000000e+00,
00071    },  },  {  { 1.8229206610e-04,-7.8997325866e-01,-7.7191410839e-01,-2.8075643964e+00,-1.6948618347e+00,-3.0367273700e+00,-9.0333559408e-01,0.0000000000e+00,
00072    },  { 9.8531161839e-02,-5.6297236492e-02,-1.1421579050e-01,-4.8122536483e-01,-4.0121072432e-01,-7.4834487567e-01,-6.9170822332e-01,0.0000000000e+00,
00073    },  },  {  { 1.8229206611e-04,-7.8997325866e-01,2.5782298908e+00,-5.3629717478e+00,6.5890882172e+00,-5.8012914776e+00,3.0171839130e+00,0.0000000000e+00,
00074    },  { 9.8534230718e-02,-5.6297236492e-02,3.8148618075e-01,-1.0848760410e+00,1.8441165168e+00,-2.4860666655e+00,2.3103384142e+00,0.0000000000e+00,
00075    },  },  {  { 1.8229206610e-04,-7.8997325866e-01,-3.8715051001e-01,-2.6192408538e+00,-8.3977994034e-01,-2.8329897913e+00,-4.5306444352e-01,0.0000000000e+00,
00076    },  { 9.8531160936e-02,-5.6297236492e-02,-5.7284484199e-02,-4.3673866734e-01,-1.9564766257e-01,-6.2028156584e-01,-3.4692356122e-01,0.0000000000e+00,
00077    },  }, 
00078 };
00079 
00080 /*! \brief Coefficients for output filter
00081  * Coefficients table, generated by program "mkfilter"
00082  * Format: coef[IDX_BW][IDX_COEF]   
00083  * IDX_COEF = 0   => 1/GAIN   
00084  * IDX_COEF = 1-6 => Coefficientes y[n]
00085 */
00086 static double coef_out[NBW][8]={
00087    { 1.3868644653e-08,-6.3283665042e-01,4.0895057217e+00,-1.1020074592e+01,1.5850766191e+01,-1.2835109292e+01,5.5477477340e+00,0.0000000000e+00,
00088    },  { 3.1262119724e-03,-7.8390522307e-03,8.5209627801e-02,-4.0804129163e-01,1.1157139955e+00,-1.8767603680e+00,1.8916395224e+00,0.0000000000e+00 
00089    }, 
00090 };
00091 
00092 /*! Integer Pass Band demodulator filter  */
00093 static inline int ibpdfilter(struct filter_struct * fs, int in)
00094 {
00095    int i,j;
00096    int s;
00097    int64_t s_interim;
00098    
00099    /* integer filter */
00100    s =  in * fs->icoefs[0];
00101    fs->ixv[(fs->ip + 6) & 7] = s;
00102    
00103    s =      (fs->ixv[fs->ip]           + fs->ixv[(fs->ip + 6) & 7]) +
00104       6  * (fs->ixv[(fs->ip + 1) & 7] + fs->ixv[(fs->ip + 5) & 7]) +
00105       15 * (fs->ixv[(fs->ip + 2) & 7] + fs->ixv[(fs->ip + 4) & 7]) +
00106       20 *  fs->ixv[(fs->ip + 3) & 7];
00107    
00108    for (i = 1, j = fs->ip; i < 7; i++, j++) {
00109       /* Promote operation to 64 bit to prevent overflow that occurred in 32 bit) */
00110       s_interim = (int64_t)(fs->iyv[j & 7]) * 
00111             (int64_t)(fs->icoefs[i]) /
00112             (int64_t)(1024);
00113       s += (int) s_interim;
00114    }
00115    fs->iyv[j & 7] = s;
00116    fs->ip++;
00117    fs->ip &= 7;
00118    return s;
00119 }
00120 
00121 /*! Integer Band Pass filter */
00122 static inline int ibpfilter(struct filter_struct * fs, int in)
00123 {
00124    int i, j;
00125    int s;
00126    int64_t s_interim;
00127    
00128    /* integer filter */
00129    s =  in * fs->icoefs[0] / 256;
00130    fs->ixv[(fs->ip + 6) & 7] = s;
00131    
00132    s = (fs->ixv[(fs->ip + 6) & 7] - fs->ixv[fs->ip])
00133       + 3 * (fs->ixv[(fs->ip + 2) & 7] - fs->ixv[(fs->ip + 4) & 7]);
00134    
00135    for (i = 1, j = fs->ip; i < 7; i++, j++) { 
00136       s_interim = (int64_t)(fs->iyv[j & 7]) * 
00137             (int64_t)(fs->icoefs[i]) / 
00138             (int64_t)(256);
00139       s += (int) s_interim;
00140    }
00141    fs->iyv[j & 7] = s;
00142    fs->ip++;
00143    fs->ip &= 7;
00144    return s;
00145 }
00146 
00147 static inline int idemodulator(fsk_data *fskd, int *retval, int x)
00148 {
00149    int is, im, id;
00150    int ilin2;
00151  
00152    is = ibpfilter(&fskd->space_filter, x);
00153    im = ibpfilter(&fskd->mark_filter, x);
00154    
00155    ilin2 = ((im * im) - (is * is)) / (256 * 256);
00156    
00157    id = ibpdfilter(&fskd->demod_filter, ilin2);
00158    
00159    *retval = id;
00160    return 0;
00161 }
00162 
00163 static int get_bit_raw(fsk_data *fskd, short *buffer, int *len)
00164 {
00165    /* This function implements a DPLL to synchronize with the bits */
00166    int f;
00167 
00168    int ix;
00169    /* PLL coeffs are set up in callerid_new */
00170    for (f = 0;;) {
00171       if (idemodulator(fskd, &ix, IGET_SAMPLE)) return(-1);
00172       if ((ix * fskd->xi0) < 0) { /* Transicion */
00173          if (!f) {
00174             if (fskd->icont < (fskd->pllispb2)) {
00175                fskd->icont += fskd->pllids; 
00176             } else {
00177                fskd->icont -= fskd->pllids;
00178             }
00179             f = 1;
00180          }
00181       }
00182       fskd->xi0 = ix;
00183       fskd->icont += 32;
00184       if (fskd->icont > fskd->pllispb) {
00185          fskd->icont -= fskd->pllispb;
00186          break;
00187       }
00188    }
00189    f = (ix > 0) ? 0x80 : 0;
00190    return f;
00191 }
00192 
00193 int fskmodem_init(fsk_data *fskd)
00194 {
00195    int i;
00196 
00197    fskd->space_filter.ip  = 0;
00198    fskd->mark_filter.ip   = 0;
00199    fskd->demod_filter.ip  = 0;
00200 
00201    for ( i = 0 ; i < 7 ; i++ ) {
00202       fskd->space_filter.icoefs[i] = 
00203          coef_in[fskd->f_space_idx][fskd->bw][i] * 256;
00204       fskd->space_filter.ixv[i] = 0;;
00205       fskd->space_filter.iyv[i] = 0;;
00206 
00207       fskd->mark_filter.icoefs[i] = 
00208          coef_in[fskd->f_mark_idx][fskd->bw][i] * 256;
00209       fskd->mark_filter.ixv[i] = 0;;
00210       fskd->mark_filter.iyv[i] = 0;;
00211 
00212       fskd->demod_filter.icoefs[i] = 
00213          coef_out[fskd->bw][i] * 1024;
00214       fskd->demod_filter.ixv[i] = 0;;
00215       fskd->demod_filter.iyv[i] = 0;;
00216    }
00217    return 0;
00218 }
00219 
00220 int fsk_serial(fsk_data *fskd, short *buffer, int *len, int *outbyte)
00221 {
00222    int a;
00223    int i, j, n1, r;
00224    int samples = 0;
00225    int olen;
00226    int beginlen = *len;
00227    int beginlenx;
00228    
00229    switch (fskd->state) {
00230       /* Pick up where we left off */
00231    case STATE_SEARCH_STARTBIT2:
00232       goto search_startbit2;
00233    case STATE_SEARCH_STARTBIT3:
00234       goto search_startbit3;
00235    case STATE_GET_BYTE:
00236       goto getbyte;
00237    }
00238    /* We await for start bit  */
00239    do {
00240       /* this was jesus's nice, reasonable, working (at least with RTTY) code
00241       to look for the beginning of the start bit. Unfortunately, since TTY/TDD's
00242       just start sending a start bit with nothing preceding it at the beginning
00243       of a transmission (what a LOSING design), we cant do it this elegantly */
00244       /* NOT USED
00245             if (demodulator(zap,&x1)) 
00246                return -1;
00247             for(;;) {
00248                if (demodulator(zap,&x2)) 
00249                   return -1;
00250                if (x1>0 && x2<0) break;
00251                x1=x2;
00252             }
00253       */
00254       /* this is now the imprecise, losing, but functional code to detect the
00255       beginning of a start bit in the TDD sceanario. It just looks for sufficient
00256       level to maybe, perhaps, guess, maybe that its maybe the beginning of
00257       a start bit, perhaps. This whole thing stinks! */
00258       beginlenx = beginlen; /* just to avoid unused war warnings */
00259       if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
00260          return -1;
00261       samples++;
00262       for(;;) {
00263 search_startbit2:       
00264          if (*len <= 0) {
00265             fskd->state = STATE_SEARCH_STARTBIT2;
00266             return 0;
00267          }
00268          samples++;
00269          if (idemodulator(fskd, &fskd->xi2, IGET_SAMPLE)) 
00270             return -1;
00271 #if 0
00272          printf("xi2 = %d ", fskd->xi2);
00273 #endif         
00274          if (fskd->xi2 < 512) {
00275             break;
00276          }
00277       }
00278 search_startbit3:       
00279       /* We await for 0.5 bits before using DPLL */
00280       i = fskd->ispb / 2;
00281       if (*len < i) {
00282          fskd->state = STATE_SEARCH_STARTBIT3;
00283          return 0;
00284       }
00285       for (; i > 0; i--) {
00286          if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
00287             return(-1); 
00288 #if 0
00289          printf("xi1 = %d ", fskd->xi1);
00290 #endif
00291          samples++; 
00292       }
00293 
00294       /* x1 must be negative (start bit confirmation) */
00295 
00296    } while (fskd->xi1 > 0);
00297    fskd->state = STATE_GET_BYTE;
00298 
00299 getbyte:
00300 
00301    /* Need at least 80 samples (for 1200) or
00302       1320 (for 45.5) to be sure we'll have a byte */
00303    if (fskd->nbit < 8) {
00304       if (*len < 1320)
00305          return 0;
00306    } else {
00307       if (*len < 80)
00308          return 0;
00309    }
00310 
00311    /* Now we read the data bits */
00312    j = fskd->nbit;
00313    for (a = n1 = 0; j; j--) {
00314       olen = *len;
00315       i = get_bit_raw(fskd, buffer, len);
00316       buffer += (olen - *len);
00317       if (i == -1) 
00318          return -1;
00319       if (i) 
00320          n1++;
00321       a >>= 1; 
00322       a |= i;
00323    }
00324    j = 8 - fskd->nbit;
00325    a >>= j;
00326 
00327    /* We read parity bit (if exists) and check parity */
00328    if (fskd->parity) {
00329       olen = *len;
00330       i = get_bit_raw(fskd, buffer, len); 
00331       buffer += (olen - *len);
00332       if (i == -1) 
00333          return -1;
00334       if (i) 
00335          n1++;
00336       if (fskd->parity == 1) {   /* parity=1 (even) */
00337          if (n1 & 1) 
00338             a |= 0x100;       /* error */
00339       } else {             /* parity=2 (odd) */
00340          if (!(n1 & 1)) 
00341             a |= 0x100;       /* error */
00342       }
00343    }
00344    
00345    /* We read STOP bits. All of them must be 1 */
00346    
00347    for (j = fskd->instop; j; j--) {
00348       r = get_bit_raw(fskd, buffer, len);
00349       if (r == -1) 
00350          return -1;
00351       if (!r) 
00352          a |= 0x200;
00353    }
00354 
00355    /* And finally we return  
00356     * Bit 8 : Parity error 
00357     * Bit 9 : Framming error
00358    */
00359       
00360    *outbyte = a;
00361    fskd->state = STATE_SEARCH_STARTBIT;
00362    return 1;
00363 }

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