fskmodem_float.c File Reference

FSK Modulator/Demodulator. More...

#include "asterisk.h"
#include <stdio.h>
#include "asterisk/fskmodem.h"

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Defines

#define BWLIST   {75,800}
#define FLIST   {1400,1800,1200,2200,1300,2100}
#define GET_SAMPLE   get_sample(&buffer, len)
#define NBW   2
#define NF   6
#define STATE_GET_BYTE   3
#define STATE_SEARCH_STARTBIT   0
#define STATE_SEARCH_STARTBIT2   1
#define STATE_SEARCH_STARTBIT3   2

Functions

static int demodulator (fsk_data *fskd, float *retval, float x)
static float filterL (fsk_data *fskd, float in)
static float filterM (fsk_data *fskd, float in)
static float filterS (fsk_data *fskd, float in)
int fsk_serial (fsk_data *fskd, short *buffer, int *len, int *outbyte)
static int get_bit_raw (fsk_data *fskd, short *buffer, int *len)
static float get_sample (short **buffer, int *len)

Variables

static double coef_in [NF][NBW][8]
 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_out [NBW][8]
 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].


Detailed Description

FSK Modulator/Demodulator.

Author:
Mark Spencer <markster@digium.com>

Definition in file fskmodem_float.c.


Define Documentation

#define BWLIST   {75,800}

Definition at line 44 of file fskmodem_float.c.

#define FLIST   {1400,1800,1200,2200,1300,2100}

Definition at line 46 of file fskmodem_float.c.

#define GET_SAMPLE   get_sample(&buffer, len)

Definition at line 62 of file fskmodem_float.c.

Referenced by fsk_serial(), and get_bit_raw().

#define NBW   2

Definition at line 43 of file fskmodem_float.c.

#define NF   6

Definition at line 45 of file fskmodem_float.c.

#define STATE_GET_BYTE   3

Definition at line 51 of file fskmodem_float.c.

Referenced by fsk_serial().

#define STATE_SEARCH_STARTBIT   0

Definition at line 48 of file fskmodem_float.c.

Referenced by fsk_serial().

#define STATE_SEARCH_STARTBIT2   1

Definition at line 49 of file fskmodem_float.c.

Referenced by fsk_serial().

#define STATE_SEARCH_STARTBIT3   2

Definition at line 50 of file fskmodem_float.c.

Referenced by fsk_serial().


Function Documentation

static int demodulator ( fsk_data fskd,
float *  retval,
float  x 
) [inline, static]

Definition at line 171 of file fskmodem_float.c.

References fsk_data::cola_demod, fsk_data::cola_filter, fsk_data::cola_in, filterL(), filterM(), filterS(), NCOLA, and fsk_data::pcola.

Referenced by fsk_serial(), and get_bit_raw().

00172 {
00173    float xS,xM;
00174 
00175    fskd->cola_in[fskd->pcola] = x;
00176 
00177    xS = filterS(fskd,x);
00178    xM = filterM(fskd,x);
00179 
00180    fskd->cola_filter[fskd->pcola] = xM-xS;
00181 
00182    x = filterL(fskd,xM*xM - xS*xS);
00183 
00184    fskd->cola_demod[fskd->pcola++] = x;
00185    fskd->pcola &=  (NCOLA-1);
00186 
00187    *retval = x;
00188    return 0;
00189 }

static float filterL ( fsk_data fskd,
float  in 
) [inline, static]

Low-pass filter for demodulated data

Definition at line 149 of file fskmodem_float.c.

References fsk_data::bw, fsk_data::flp, fsk_data::flxv, and fsk_data::flyv.

Referenced by demodulator().

00150 {
00151    int i, j;
00152    double s;
00153    double *pc;
00154 
00155    pc = &coef_out[fskd->bw][0];
00156    fskd->flxv[(fskd->flp + 6) & 7] = in * (*pc++);
00157 
00158    s = (fskd->flxv[fskd->flp] + fskd->flxv[(fskd->flp+6)&7]) +
00159      6  * (fskd->flxv[(fskd->flp+1)&7] + fskd->flxv[(fskd->flp+5)&7]) +
00160      15 * (fskd->flxv[(fskd->flp+2)&7] + fskd->flxv[(fskd->flp+4)&7]) +
00161      20 *  fskd->flxv[(fskd->flp+3)&7];
00162 
00163    for (i = 0,j = fskd->flp;i<6;i++,j++)
00164       s += fskd->flyv[j&7]*(*pc++);
00165    fskd->flyv[j&7] = s;
00166    fskd->flp++;
00167    fskd->flp &= 7;
00168    return s;
00169 }

static float filterM ( fsk_data fskd,
float  in 
) [inline, static]

Band-pass filter for MARK frequency

Definition at line 111 of file fskmodem_float.c.

References fsk_data::bw, fsk_data::f_mark_idx, fsk_data::fmp, fsk_data::fmxv, and fsk_data::fmyv.

Referenced by demodulator().

00112 {
00113    int i, j;
00114    double s;
00115    double *pc;
00116 
00117    pc = &coef_in[fskd->f_mark_idx][fskd->bw][0];
00118    fskd->fmxv[(fskd->fmp+6)&7] = in*(*pc++);
00119 
00120    s = (fskd->fmxv[(fskd->fmp + 6) & 7] - fskd->fmxv[fskd->fmp]) + 3 * (fskd->fmxv[(fskd->fmp + 2) & 7] - fskd->fmxv[(fskd->fmp + 4) & 7]);
00121    for (i = 0, j = fskd->fmp; i < 6; i++, j++)
00122       s += fskd->fmyv[j&7]*(*pc++);
00123    fskd->fmyv[j&7] = s;
00124    fskd->fmp++;
00125    fskd->fmp &= 7;
00126    return s;
00127 }

static float filterS ( fsk_data fskd,
float  in 
) [inline, static]

Band-pass filter for SPACE frequency

Definition at line 130 of file fskmodem_float.c.

References fsk_data::bw, fsk_data::f_space_idx, fsk_data::fsp, fsk_data::fsxv, and fsk_data::fsyv.

Referenced by demodulator().

00131 {
00132    int i, j;
00133    double s;
00134    double *pc;
00135 
00136    pc = &coef_in[fskd->f_space_idx][fskd->bw][0];
00137    fskd->fsxv[(fskd->fsp+6)&7] = in*(*pc++);
00138 
00139    s = (fskd->fsxv[(fskd->fsp + 6) & 7] - fskd->fsxv[fskd->fsp]) + 3 * (fskd->fsxv[(fskd->fsp + 2) & 7] - fskd->fsxv[(fskd->fsp + 4) & 7]);
00140    for (i = 0, j = fskd->fsp; i < 6; i++, j++)
00141       s += fskd->fsyv[j&7]*(*pc++);
00142    fskd->fsyv[j&7] = s;
00143    fskd->fsp++;
00144    fskd->fsp &= 7;
00145    return s;
00146 }

int fsk_serial ( fsk_data fskd,
short *  buffer,
int *  len,
int *  outbyte 
)

Definition at line 226 of file fskmodem_float.c.

References a, demodulator(), get_bit_raw(), GET_SAMPLE, fsk_data::nbit, fsk_data::nstop, fsk_data::parity, ast_frame::samples, fsk_data::spb, fsk_data::state, STATE_GET_BYTE, STATE_SEARCH_STARTBIT, STATE_SEARCH_STARTBIT2, STATE_SEARCH_STARTBIT3, fsk_data::x1, and fsk_data::x2.

00227 {
00228    int a;
00229    int i,j,n1,r;
00230    int samples = 0;
00231    int olen;
00232 
00233    switch (fskd->state) {
00234       /* Pick up where we left off */
00235    case STATE_SEARCH_STARTBIT2:
00236       goto search_startbit2;
00237    case STATE_SEARCH_STARTBIT3:
00238       goto search_startbit3;
00239    case STATE_GET_BYTE:
00240       goto getbyte;
00241    }
00242    /* We await for start bit  */
00243    do {
00244       /* this was jesus's nice, reasonable, working (at least with RTTY) code
00245       to look for the beginning of the start bit. Unfortunately, since TTY/TDD's
00246       just start sending a start bit with nothing preceding it at the beginning
00247       of a transmission (what a LOSING design), we cant do it this elegantly */
00248       /*
00249       if (demodulator(zap,&x1)) return(-1);
00250       for (;;) {
00251          if (demodulator(zap,&x2)) return(-1);
00252          if (x1>0 && x2<0) break;
00253          x1 = x2;
00254       }
00255       */
00256       /* this is now the imprecise, losing, but functional code to detect the
00257       beginning of a start bit in the TDD sceanario. It just looks for sufficient
00258       level to maybe, perhaps, guess, maybe that its maybe the beginning of
00259       a start bit, perhaps. This whole thing stinks! */
00260       if (demodulator(fskd, &fskd->x1, GET_SAMPLE))
00261          return -1;
00262       samples++;
00263       for (;;) {
00264 search_startbit2:
00265          if (*len <= 0) {
00266             fskd->state  =  STATE_SEARCH_STARTBIT2;
00267             return 0;
00268          }
00269          samples++;
00270          if (demodulator(fskd, &fskd->x2, GET_SAMPLE))
00271             return(-1);
00272 #if 0
00273          printf("x2  =  %5.5f ", fskd->x2);
00274 #endif
00275          if (fskd->x2 < -0.5)
00276             break;
00277       }
00278 search_startbit3:
00279       /* We await for 0.5 bits before using DPLL */
00280       i = fskd->spb/2;
00281       if (*len < i) {
00282          fskd->state = STATE_SEARCH_STARTBIT3;
00283          return 0;
00284       }
00285       for (; i>0; i--) {
00286          if (demodulator(fskd, &fskd->x1, GET_SAMPLE))
00287             return(-1);
00288 #if 0
00289          printf("x1 = %5.5f ", fskd->x1);
00290 #endif
00291          samples++;
00292       }
00293 
00294       /* x1 must be negative (start bit confirmation) */
00295 
00296    } while (fskd->x1 > 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    /* Now we read the data bits */
00311    j = fskd->nbit;
00312    for (a = n1 = 0; j; j--) {
00313       olen = *len;
00314       i = get_bit_raw(fskd, buffer, len);
00315       buffer += (olen - *len);
00316       if (i == -1)
00317          return(-1);
00318       if (i)
00319          n1++;
00320       a >>= 1;
00321       a |= i;
00322    }
00323    j = 8-fskd->nbit;
00324    a >>= j;
00325 
00326    /* We read parity bit (if exists) and check parity */
00327    if (fskd->parity) {
00328       olen = *len;
00329       i = get_bit_raw(fskd, buffer, len);
00330       buffer += (olen - *len);
00331       if (i == -1)
00332          return(-1);
00333       if (i)
00334          n1++;
00335       if (fskd->parity == 1) {   /* parity=1 (even) */
00336          if (n1&1)
00337             a |= 0x100;    /* error */
00338       } else {       /* parity=2 (odd) */
00339          if (!(n1&1))
00340             a |= 0x100; /* error */
00341       }
00342    }
00343 
00344    /* We read STOP bits. All of them must be 1 */
00345 
00346    for (j = fskd->nstop;j;j--) {
00347       r = get_bit_raw(fskd, buffer, len);
00348       if (r == -1)
00349          return(-1);
00350       if (!r)
00351          a |= 0x200;
00352    }
00353 
00354    /* And finally we return  */
00355    /* Bit 8 : Parity error */
00356    /* Bit 9 : Framming error*/
00357 
00358    *outbyte = a;
00359    fskd->state = STATE_SEARCH_STARTBIT;
00360    return 1;
00361 }

static int get_bit_raw ( fsk_data fskd,
short *  buffer,
int *  len 
) [static]

Definition at line 191 of file fskmodem_float.c.

References fsk_data::cont, demodulator(), f, GET_SAMPLE, fsk_data::spb, and fsk_data::x0.

Referenced by fsk_serial().

00192 {
00193    /* This function implements a DPLL to synchronize with the bits */
00194    float x,spb,spb2,ds;
00195    int f;
00196 
00197    spb = fskd->spb;
00198    if (fskd->spb == 7)
00199       spb = 8000.0 / 1200.0;
00200    ds = spb/32.;
00201    spb2 = spb/2.;
00202 
00203    for (f = 0;;) {
00204       if (demodulator(fskd, &x, GET_SAMPLE))
00205          return -1;
00206       if ((x * fskd->x0) < 0) {  /* Transition */
00207          if (!f) {
00208             if (fskd->cont<(spb2))
00209                fskd->cont += ds;
00210             else
00211                fskd->cont -= ds;
00212             f = 1;
00213          }
00214       }
00215       fskd->x0 = x;
00216       fskd->cont += 1.;
00217       if (fskd->cont > spb) {
00218          fskd->cont -= spb;
00219          break;
00220       }
00221    }
00222    f = (x > 0) ? 0x80 : 0;
00223    return f;
00224 }

static float get_sample ( short **  buffer,
int *  len 
) [inline, static]

Definition at line 53 of file fskmodem_float.c.

References retval.

00054 {
00055    float retval;
00056    retval = (float) **buffer / 256;
00057    (*buffer)++;
00058    (*len)--;
00059    return retval;
00060 };


Variable Documentation

double coef_in[NF][NBW][8] [static]

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].

Definition at line 71 of file fskmodem_float.c.

double coef_out[NBW][8] [static]

Initial value:

 {
   { 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, },
}
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].

Definition at line 104 of file fskmodem_float.c.


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