2 * Asterisk -- A telephony toolkit for Linux.
4 * FSK Modulator/Demodulator
6 * Copyright (C) 1999, Mark Spencer
8 * Mark Spencer <markster@linux-support.net>
10 * This program is free software, distributed under the terms of
11 * the GNU General Public License.
13 * Includes code and algorithms from the Zapata library.
17 #include <asterisk/fskmodem.h>
22 #define BWLIST {75,800}
24 #define FLIST {1400,1800,1200,2200}
26 #define STATE_SEARCH_STARTBIT 0
27 #define STATE_SEARCH_STARTBIT2 1
28 #define STATE_SEARCH_STARTBIT3 2
29 #define STATE_GET_BYTE 3
31 static inline float get_sample(short **buffer, int *len)
34 retval = (float) **buffer / 256;
40 #define GET_SAMPLE get_sample(&buffer, len)
42 /* Coeficientes para filtros de entrada */
43 /* Tabla de coeficientes, generada a partir del programa "mkfilter" */
44 /* Formato: coef[IDX_FREC][IDX_BW][IDX_COEF] */
45 /* IDX_COEF=0 => 1/GAIN */
46 /* IDX_COEF=1-6 => Coeficientes y[n] */
48 static double coef_in[NF][NBW][8]={
52 /* Coeficientes para filtro de salida */
53 /* Tabla de coeficientes, generada a partir del programa "mkfilter" */
54 /* Formato: coef[IDX_BW][IDX_COEF] */
55 /* IDX_COEF=0 => 1/GAIN */
56 /* IDX_COEF=1-6 => Coeficientes y[n] */
58 static double coef_out[NBW][8]={
63 /* Filtro pasa-banda para frecuencia de MARCA */
64 static inline float filtroM(fsk_data *fskd,float in)
70 pc=&coef_in[fskd->f_mark_idx][fskd->bw][0];
71 fskd->fmxv[(fskd->fmp+6)&7]=in*(*pc++);
73 s=(fskd->fmxv[(fskd->fmp+6)&7] - fskd->fmxv[fskd->fmp]) + 3 * (fskd->fmxv[(fskd->fmp+2)&7] - fskd->fmxv[(fskd->fmp+4)&7]);
74 for (i=0,j=fskd->fmp;i<6;i++,j++) s+=fskd->fmyv[j&7]*(*pc++);
76 fskd->fmp++; fskd->fmp&=7;
80 /* Filtro pasa-banda para frecuencia de ESPACIO */
81 static inline float filtroS(fsk_data *fskd,float in)
87 pc=&coef_in[fskd->f_space_idx][fskd->bw][0];
88 fskd->fsxv[(fskd->fsp+6)&7]=in*(*pc++);
90 s=(fskd->fsxv[(fskd->fsp+6)&7] - fskd->fsxv[fskd->fsp]) + 3 * (fskd->fsxv[(fskd->fsp+2)&7] - fskd->fsxv[(fskd->fsp+4)&7]);
91 for (i=0,j=fskd->fsp;i<6;i++,j++) s+=fskd->fsyv[j&7]*(*pc++);
93 fskd->fsp++; fskd->fsp&=7;
97 /* Filtro pasa-bajos para datos demodulados */
98 static inline float filtroL(fsk_data *fskd,float in)
104 pc=&coef_out[fskd->bw][0];
105 fskd->flxv[(fskd->flp + 6) & 7]=in * (*pc++);
107 s= (fskd->flxv[fskd->flp] + fskd->flxv[(fskd->flp+6)&7]) +
108 6 * (fskd->flxv[(fskd->flp+1)&7] + fskd->flxv[(fskd->flp+5)&7]) +
109 15 * (fskd->flxv[(fskd->flp+2)&7] + fskd->flxv[(fskd->flp+4)&7]) +
110 20 * fskd->flxv[(fskd->flp+3)&7];
112 for (i=0,j=fskd->flp;i<6;i++,j++) s+=fskd->flyv[j&7]*(*pc++);
114 fskd->flp++; fskd->flp&=7;
118 static inline int demodulador(fsk_data *fskd, float *retval, float x)
122 fskd->cola_in[fskd->pcola]=x;
127 fskd->cola_filtro[fskd->pcola]=xM-xS;
129 x=filtroL(fskd,xM*xM - xS*xS);
131 fskd->cola_demod[fskd->pcola++]=x;
132 fskd->pcola &= (NCOLA-1);
138 static int get_bit_raw(fsk_data *fskd, short *buffer, int *len)
140 /* Esta funcion implementa un DPLL para sincronizarse con los bits */
145 if (fskd->spb == 7) spb = 8000.0 / 1200.0;
150 if (demodulador(fskd,&x, GET_SAMPLE)) return(-1);
151 if ((x*fskd->x0)<0) { /* Transicion */
153 if (fskd->cont<(spb2)) fskd->cont+=ds; else fskd->cont-=ds;
159 if (fskd->cont>spb) {
168 int fsk_serie(fsk_data *fskd, short *buffer, int *len, int *outbyte)
174 switch(fskd->state) {
175 /* Pick up where we left off */
176 case STATE_SEARCH_STARTBIT2:
177 goto search_startbit2;
178 case STATE_SEARCH_STARTBIT3:
179 goto search_startbit3;
183 /* Esperamos bit de start */
185 /* this was jesus's nice, reasonable, working (at least with RTTY) code
186 to look for the beginning of the start bit. Unfortunately, since TTY/TDD's
187 just start sending a start bit with nothing preceding it at the beginning
188 of a transmission (what a LOSING design), we cant do it this elegantly */
190 if (demodulador(zap,&x1)) return(-1);
192 if (demodulador(zap,&x2)) return(-1);
193 if (x1>0 && x2<0) break;
197 /* this is now the imprecise, losing, but functional code to detect the
198 beginning of a start bit in the TDD sceanario. It just looks for sufficient
199 level to maybe, perhaps, guess, maybe that its maybe the beginning of
200 a start bit, perhaps. This whole thing stinks! */
201 if (demodulador(fskd,&fskd->x1,GET_SAMPLE)) return(-1);
207 fskd->state = STATE_SEARCH_STARTBIT2;
211 if (demodulador(fskd,&fskd->x2,GET_SAMPLE)) return(-1);
213 printf("x2 = %5.5f ", fskd->x2);
215 if (fskd->x2 < -0.5) break;
218 /* Esperamos 0.5 bits antes de usar DPLL */
221 fskd->state = STATE_SEARCH_STARTBIT3;
224 for(;i;i--) { if (demodulador(fskd,&fskd->x1,GET_SAMPLE)) return(-1);
226 printf("x1 = %5.5f ", fskd->x1);
230 /* x1 debe ser negativo (confirmación del bit de start) */
232 } while (fskd->x1>0);
233 fskd->state = STATE_GET_BYTE;
237 /* Need at least 80 samples to be sure we'll have a byte */
241 /* Leemos ahora los bits de datos */
245 i=get_bit_raw(fskd, buffer, len);
246 buffer += (olen - *len);
247 if (i == -1) return(-1);
254 /* Leemos bit de paridad (si existe) y la comprobamos */
257 i=get_bit_raw(fskd, buffer, len);
258 buffer += (olen - *len);
259 if (i == -1) return(-1);
261 if (fskd->paridad==1) { /* paridad=1 (par) */
262 if (n1&1) a|=0x100; /* error */
263 } else { /* paridad=2 (impar) */
264 if (!(n1&1)) a|=0x100; /* error */
268 /* Leemos bits de STOP. Todos deben ser 1 */
270 for (j=fskd->nstop;j;j--) {
271 r = get_bit_raw(fskd, buffer, len);
272 if (r == -1) return(-1);
276 /* Por fin retornamos */
277 /* Bit 8 : Error de paridad */
278 /* Bit 9 : Error de Framming */
281 fskd->state = STATE_SEARCH_STARTBIT;