fskmodem_float.c

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2005, Digium, Inc.
 *
 * Mark Spencer <markster@digium.com>
 *
 * 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 <markster@digium.com>
 *
 * \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 : Framing error*/

	*outbyte = a;
	fskd->state = STATE_SEARCH_STARTBIT;
	return 1;
}