fskmodem_float.c

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/*
 * 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 <stdio.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 float get_sample(short **buffer, int *len)
{
 float retval;
 retval = (float) **buffer / 256;
 (*buffer)++;
 (*len)--;
 return retval;
};

#define GET_SAMPLE get_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, },
};


/*! Band-pass filter for MARK frequency */
static inline float filterM(fsk_data *fskd,float in)
{
 int i, j;
 double s;
 double *pc;

 pc = &coef_in[fskd->f_mark_idx][fskd->bw][0];
 fskd->fmxv[(fskd->fmp+6)&7] = in*(*pc++);

 s = (fskd->fmxv[(fskd->fmp + 6) & 7] - fskd->fmxv[fskd->fmp]) + 3 * (fskd->fmxv[(fskd->fmp + 2) & 7] - fskd->fmxv[(fskd->fmp + 4) & 7]);
 for (i = 0, j = fskd->fmp; i < 6; i++, j++)
 s += fskd->fmyv[j&7]*(*pc++);
 fskd->fmyv[j&7] = s;
 fskd->fmp++;
 fskd->fmp &= 7;
 return s;
}

/*! Band-pass filter for SPACE frequency */
static inline float filterS(fsk_data *fskd,float in)
{
 int i, j;
 double s;
 double *pc;

 pc = &coef_in[fskd->f_space_idx][fskd->bw][0];
 fskd->fsxv[(fskd->fsp+6)&7] = in*(*pc++);

 s = (fskd->fsxv[(fskd->fsp + 6) & 7] - fskd->fsxv[fskd->fsp]) + 3 * (fskd->fsxv[(fskd->fsp + 2) & 7] - fskd->fsxv[(fskd->fsp + 4) & 7]);
 for (i = 0, j = fskd->fsp; i < 6; i++, j++)
 s += fskd->fsyv[j&7]*(*pc++);
 fskd->fsyv[j&7] = s;
 fskd->fsp++;
 fskd->fsp &= 7;
 return s;
}

/*! Low-pass filter for demodulated data */
static inline float filterL(fsk_data *fskd,float in)
{
 int i, j;
 double s;
 double *pc;

 pc = &coef_out[fskd->bw][0];
 fskd->flxv[(fskd->flp + 6) & 7] = in * (*pc++);

 s = (fskd->flxv[fskd->flp] + fskd->flxv[(fskd->flp+6)&7]) +
 6 * (fskd->flxv[(fskd->flp+1)&7] + fskd->flxv[(fskd->flp+5)&7]) +
 15 * (fskd->flxv[(fskd->flp+2)&7] + fskd->flxv[(fskd->flp+4)&7]) +
 20 * fskd->flxv[(fskd->flp+3)&7];

 for (i = 0,j = fskd->flp;i<6;i++,j++)
 s += fskd->flyv[j&7]*(*pc++);
 fskd->flyv[j&7] = s;
 fskd->flp++;
 fskd->flp &= 7;
 return s;
}

static inline int demodulator(fsk_data *fskd, float *retval, float x)
{
 float xS,xM;

 fskd->cola_in[fskd->pcola] = x;

 xS = filterS(fskd,x);
 xM = filterM(fskd,x);

 fskd->cola_filter[fskd->pcola] = xM-xS;

 x = filterL(fskd,xM*xM - xS*xS);

 fskd->cola_demod[fskd->pcola++] = x;
 fskd->pcola &= (NCOLA-1);

 *retval = x;
 return 0;
}

static int get_bit_raw(fsk_data *fskd, short *buffer, int *len)
{
 /* This function implements a DPLL to synchronize with the bits */
 float x,spb,spb2,ds;
 int f;

 spb = fskd->spb;
 if (fskd->spb == 7)
 spb = 8000.0 / 1200.0;
 ds = spb/32.;
 spb2 = spb/2.;

 for (f = 0;;) {
 if (demodulator(fskd, &x, GET_SAMPLE))
 return -1;
 if ((x * fskd->x0) < 0) { /* Transition */
 if (!f) {
 if (fskd->cont<(spb2))
 fskd->cont += ds;
 else
 fskd->cont -= ds;
 f = 1;
 }
 }
 fskd->x0 = x;
 fskd->cont += 1.;
 if (fskd->cont > spb) {
 fskd->cont -= spb;
 break;
 }
 }
 f = (x > 0) ? 0x80 : 0;
 return f;
}

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

 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 */
 /*
 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! */
 if (demodulator(fskd, &fskd->x1, GET_SAMPLE))
 return -1;
 samples++;
 for (;;) {
search_startbit2:
 if (*len <= 0) {
 fskd->state = STATE_SEARCH_STARTBIT2;
 return 0;
 }
 samples++;
 if (demodulator(fskd, &fskd->x2, GET_SAMPLE))
 return(-1);
#if 0
 printf("x2 = %5.5f ", fskd->x2);
#endif
 if (fskd->x2 < -0.5)
 break;
 }
search_startbit3:
 /* We await for 0.5 bits before using DPLL */
 i = fskd->spb/2;
 if (*len < i) {
 fskd->state = STATE_SEARCH_STARTBIT3;
 return 0;
 }
 for (; i>0; i--) {
 if (demodulator(fskd, &fskd->x1, GET_SAMPLE))
 return(-1);
#if 0
 printf("x1 = %5.5f ", fskd->x1);
#endif
 samples++;
 }

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

 } while (fskd->x1 > 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->nstop;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;
}