Mon May 14 04:42:56 2007

Asterisk developer's documentation


fskmodem.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 #include "asterisk.h"
00031 
00032 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
00033 
00034 #include <stdio.h>
00035 
00036 #include "asterisk/fskmodem.h"
00037 
00038 #define NBW 2
00039 #define BWLIST {75,800}
00040 #define  NF 6
00041 #define  FLIST {1400,1800,1200,2200,1300,2100}
00042 
00043 #define STATE_SEARCH_STARTBIT 0
00044 #define STATE_SEARCH_STARTBIT2   1
00045 #define STATE_SEARCH_STARTBIT3   2
00046 #define STATE_GET_BYTE        3
00047 
00048 static inline float get_sample(short **buffer, int *len)
00049 {
00050    float retval;
00051    retval = (float) **buffer / 256;
00052    (*buffer)++;
00053    (*len)--;
00054    return retval;
00055 }
00056 
00057 #define GET_SAMPLE get_sample(&buffer, len)
00058 
00059 /* Coeficientes para filtros de entrada               */
00060 /* Tabla de coeficientes, generada a partir del programa "mkfilter"  */
00061 /* Formato: coef[IDX_FREC][IDX_BW][IDX_COEF]          */
00062 /* IDX_COEF=0  => 1/GAIN                  */
00063 /* IDX_COEF=1-6   => Coeficientes y[n]          */
00064 
00065 static double coef_in[NF][NBW][8]={
00066 #include "coef_in.h"
00067 };
00068 
00069 /* Coeficientes para filtro de salida              */
00070 /* Tabla de coeficientes, generada a partir del programa "mkfilter"  */
00071 /* Formato: coef[IDX_BW][IDX_COEF]              */
00072 /* IDX_COEF=0  => 1/GAIN                  */
00073 /* IDX_COEF=1-6   => Coeficientes y[n]          */
00074 
00075 static double coef_out[NBW][8]={
00076 #include "coef_out.h"
00077 };
00078 
00079 
00080 /*! Filtro pasa-banda para frecuencia de MARCA */
00081 static inline float filtroM(fsk_data *fskd,float in)
00082 {
00083    int i,j;
00084    double s;
00085    double *pc;
00086    
00087    pc=&coef_in[fskd->f_mark_idx][fskd->bw][0];
00088    fskd->fmxv[(fskd->fmp+6)&7]=in*(*pc++);
00089    
00090    s=(fskd->fmxv[(fskd->fmp+6)&7] - fskd->fmxv[fskd->fmp]) + 3 * (fskd->fmxv[(fskd->fmp+2)&7] - fskd->fmxv[(fskd->fmp+4)&7]);
00091    for (i=0,j=fskd->fmp;i<6;i++,j++) s+=fskd->fmyv[j&7]*(*pc++);
00092    fskd->fmyv[j&7]=s;
00093    fskd->fmp++; fskd->fmp&=7;
00094    return s;
00095 }
00096 
00097 /*! Filtro pasa-banda para frecuencia de ESPACIO */
00098 static inline float filtroS(fsk_data *fskd,float in)
00099 {
00100    int i,j;
00101    double s;
00102    double *pc;
00103    
00104    pc=&coef_in[fskd->f_space_idx][fskd->bw][0];
00105    fskd->fsxv[(fskd->fsp+6)&7]=in*(*pc++);
00106    
00107    s=(fskd->fsxv[(fskd->fsp+6)&7] - fskd->fsxv[fskd->fsp]) + 3 * (fskd->fsxv[(fskd->fsp+2)&7] - fskd->fsxv[(fskd->fsp+4)&7]);
00108    for (i=0,j=fskd->fsp;i<6;i++,j++) s+=fskd->fsyv[j&7]*(*pc++);
00109    fskd->fsyv[j&7]=s;
00110    fskd->fsp++; fskd->fsp&=7;
00111    return s;
00112 }
00113 
00114 /*! Filtro pasa-bajos para datos demodulados */
00115 static inline float filtroL(fsk_data *fskd,float in)
00116 {
00117    int i,j;
00118    double s;
00119    double *pc;
00120    
00121    pc=&coef_out[fskd->bw][0];
00122    fskd->flxv[(fskd->flp + 6) & 7]=in * (*pc++); 
00123    
00124    s=     (fskd->flxv[fskd->flp]       + fskd->flxv[(fskd->flp+6)&7]) +
00125      6  * (fskd->flxv[(fskd->flp+1)&7] + fskd->flxv[(fskd->flp+5)&7]) +
00126      15 * (fskd->flxv[(fskd->flp+2)&7] + fskd->flxv[(fskd->flp+4)&7]) +
00127      20 *  fskd->flxv[(fskd->flp+3)&7]; 
00128    
00129    for (i=0,j=fskd->flp;i<6;i++,j++) s+=fskd->flyv[j&7]*(*pc++);
00130    fskd->flyv[j&7]=s;
00131    fskd->flp++; fskd->flp&=7;
00132    return s;
00133 }
00134 
00135 static inline int demodulador(fsk_data *fskd, float *retval, float x)
00136 {
00137    float xS,xM;
00138 
00139    fskd->cola_in[fskd->pcola]=x;
00140    
00141    xS=filtroS(fskd,x);
00142    xM=filtroM(fskd,x);
00143 
00144    fskd->cola_filtro[fskd->pcola]=xM-xS;
00145 
00146    x=filtroL(fskd,xM*xM - xS*xS);
00147    
00148    fskd->cola_demod[fskd->pcola++]=x;
00149    fskd->pcola &= (NCOLA-1);
00150 
00151    *retval = x;
00152    return(0);
00153 }
00154 
00155 static int get_bit_raw(fsk_data *fskd, short *buffer, int *len)
00156 {
00157    /* Esta funcion implementa un DPLL para sincronizarse con los bits */
00158    float x,spb,spb2,ds;
00159    int f;
00160 
00161    spb=fskd->spb; 
00162    if (fskd->spb == 7) spb = 8000.0 / 1200.0;
00163    ds=spb/32.;
00164    spb2=spb/2.;
00165 
00166    for (f=0;;){
00167       if (demodulador(fskd,&x, GET_SAMPLE)) return(-1);
00168       if ((x*fskd->x0)<0) {   /* Transicion */
00169          if (!f) {
00170             if (fskd->cont<(spb2)) fskd->cont+=ds; else fskd->cont-=ds;
00171             f=1;
00172          }
00173       }
00174       fskd->x0=x;
00175       fskd->cont+=1.;
00176       if (fskd->cont>spb) {
00177          fskd->cont-=spb;
00178          break;
00179       }
00180    }
00181    f=(x>0)?0x80:0;
00182    return(f);
00183 }
00184 
00185 int fsk_serie(fsk_data *fskd, short *buffer, int *len, int *outbyte)
00186 {
00187    int a;
00188    int i,j,n1,r;
00189    int samples=0;
00190    int olen;
00191    switch(fskd->state) {
00192       /* Pick up where we left off */
00193    case STATE_SEARCH_STARTBIT2:
00194       goto search_startbit2;
00195    case STATE_SEARCH_STARTBIT3:
00196       goto search_startbit3;
00197    case STATE_GET_BYTE:
00198       goto getbyte;
00199    }
00200    /* Esperamos bit de start  */
00201    do {
00202 /* this was jesus's nice, reasonable, working (at least with RTTY) code
00203 to look for the beginning of the start bit. Unfortunately, since TTY/TDD's
00204 just start sending a start bit with nothing preceding it at the beginning
00205 of a transmission (what a LOSING design), we cant do it this elegantly */
00206 /*
00207       if (demodulador(zap,&x1)) return(-1);
00208       for(;;) {
00209          if (demodulador(zap,&x2)) return(-1);
00210          if (x1>0 && x2<0) break;
00211          x1=x2;
00212       }
00213 */
00214 /* this is now the imprecise, losing, but functional code to detect the
00215 beginning of a start bit in the TDD sceanario. It just looks for sufficient
00216 level to maybe, perhaps, guess, maybe that its maybe the beginning of
00217 a start bit, perhaps. This whole thing stinks! */
00218       if (demodulador(fskd,&fskd->x1,GET_SAMPLE)) return(-1);
00219       samples++;
00220       for(;;)
00221          {
00222 search_startbit2:       
00223          if (!*len) {
00224             fskd->state = STATE_SEARCH_STARTBIT2;
00225             return 0;
00226          }
00227          samples++;
00228          if (demodulador(fskd,&fskd->x2,GET_SAMPLE)) return(-1);
00229 #if 0
00230          printf("x2 = %5.5f ", fskd->x2);
00231 #endif         
00232          if (fskd->x2 < -0.5) break; 
00233          }
00234 search_startbit3:       
00235       /* Esperamos 0.5 bits antes de usar DPLL */
00236       i=fskd->spb/2;
00237       if (*len < i) {
00238          fskd->state = STATE_SEARCH_STARTBIT3;
00239          return 0;
00240       }
00241       for(;i;i--) { if (demodulador(fskd,&fskd->x1,GET_SAMPLE)) return(-1); 
00242 #if 0
00243          printf("x1 = %5.5f ", fskd->x1);
00244 #endif         
00245    samples++; }
00246 
00247       /* x1 debe ser negativo (confirmación del bit de start) */
00248 
00249    } while (fskd->x1>0);
00250    fskd->state = STATE_GET_BYTE;
00251 
00252 getbyte:
00253 
00254    /* Need at least 80 samples (for 1200) or
00255       1320 (for 45.5) to be sure we'll have a byte */
00256    if (fskd->nbit < 8) {
00257       if (*len < 1320)
00258          return 0;
00259    } else {
00260       if (*len < 80)
00261          return 0;
00262    }
00263    /* Leemos ahora los bits de datos */
00264    j=fskd->nbit;
00265    for (a=n1=0;j;j--) {
00266       olen = *len;
00267       i=get_bit_raw(fskd, buffer, len);
00268       buffer += (olen - *len);
00269       if (i == -1) return(-1);
00270       if (i) n1++;
00271       a>>=1; a|=i;
00272    }
00273    j=8-fskd->nbit;
00274    a>>=j;
00275 
00276    /* Leemos bit de paridad (si existe) y la comprobamos */
00277    if (fskd->paridad) {
00278       olen = *len;
00279       i=get_bit_raw(fskd, buffer, len); 
00280       buffer += (olen - *len);
00281       if (i == -1) return(-1);
00282       if (i) n1++;
00283       if (fskd->paridad==1) { /* paridad=1 (par) */
00284          if (n1&1) a|=0x100;     /* error */
00285       } else {       /* paridad=2 (impar) */
00286          if (!(n1&1)) a|=0x100;  /* error */
00287       }
00288    }
00289    
00290    /* Leemos bits de STOP. Todos deben ser 1 */
00291    
00292    for (j=fskd->nstop;j;j--) {
00293       r = get_bit_raw(fskd, buffer, len);
00294       if (r == -1) return(-1);
00295       if (!r) a|=0x200;
00296    }
00297 
00298    /* Por fin retornamos  */
00299    /* Bit 8 : Error de paridad */
00300    /* Bit 9 : Error de Framming */
00301 
00302    *outbyte = a;
00303    fskd->state = STATE_SEARCH_STARTBIT;
00304    return 1;
00305 }

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