fskmodem_float.c File Reference

FSK Modulator/Demodulator. More...

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

Include dependency graph for fskmodem_float.c:

This graph shows which files directly or indirectly include this file:

Go to the source code of this file.

Macros
#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)
	Retrieve a serial byte into outbyte. Buffer is a pointer into a series of shorts and len records the number of bytes in the buffer. len will be overwritten with the number of bytes left that were not consumed.
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 marks.nosp@m.ter@.nosp@m.digiu.nosp@m.m.co.nosp@m.m

• Includes code and algorithms from the Zapata library.

Definition in file fskmodem_float.c.

Macro Definition Documentation

BWLIST

#define BWLIST   {75,800}

Definition at line 42 of file fskmodem_float.c.

FLIST

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

Definition at line 44 of file fskmodem_float.c.

GET_SAMPLE

#define GET_SAMPLE   get_sample(&buffer, len)

Definition at line 60 of file fskmodem_float.c.

NBW

#define NBW   2

Definition at line 41 of file fskmodem_float.c.

NF

#define NF   6

Definition at line 43 of file fskmodem_float.c.

STATE_GET_BYTE

#define STATE_GET_BYTE   3

Definition at line 49 of file fskmodem_float.c.

STATE_SEARCH_STARTBIT

#define STATE_SEARCH_STARTBIT   0

Definition at line 46 of file fskmodem_float.c.

STATE_SEARCH_STARTBIT2

#define STATE_SEARCH_STARTBIT2   1

Definition at line 47 of file fskmodem_float.c.

STATE_SEARCH_STARTBIT3

#define STATE_SEARCH_STARTBIT3   2

Definition at line 48 of file fskmodem_float.c.

Function Documentation

demodulator()

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

inlinestatic

Definition at line 169 of file fskmodem_float.c.

{
    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;
}

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().

filterL()

static float filterL ( fsk_data *  fskd, float  in  )

inlinestatic

Low-pass filter for demodulated data

Definition at line 147 of file fskmodem_float.c.

{
    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;
}

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

Referenced by demodulator().

filterM()

static float filterM ( fsk_data *  fskd, float  in  )

inlinestatic

Band-pass filter for MARK frequency

Definition at line 109 of file fskmodem_float.c.

{
    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;
}

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

Referenced by demodulator().

filterS()

static float filterS ( fsk_data *  fskd, float  in  )

inlinestatic

Band-pass filter for SPACE frequency

Definition at line 128 of file fskmodem_float.c.

{
    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;
}

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

Referenced by demodulator().

fsk_serial()

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

Retrieve a serial byte into outbyte. Buffer is a pointer into a series of shorts and len records the number of bytes in the buffer. len will be overwritten with the number of bytes left that were not consumed.

Return values

0	Still looking for something...
1	An output byte was received and stored in outbyte
-1	An error occured in the transmission He must be called with at least 80 bytes of buffer.

Definition at line 224 of file fskmodem_float.c.

{
    int a;
    int i,j,n1,r;
    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;
        for (;;) {
search_startbit2:
            if (*len <= 0) {
                fskd->state  =  STATE_SEARCH_STARTBIT2;
                return 0;
            }
            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
        }
 
        /* 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;
}

get_bit_raw()

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

static

Definition at line 189 of file fskmodem_float.c.

{
    /* 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;
}

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

Referenced by fsk_serial().

get_sample()

static float get_sample ( short **  buffer, int *  len  )

inlinestatic

Definition at line 51 of file fskmodem_float.c.

{
    float retval;
    retval = (float) **buffer / 256;
    (*buffer)++;
    (*len)--;
    return retval;
};

Variable Documentation

coef_in

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 69 of file fskmodem_float.c.

                                    {
 {
    { 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, },
  },
};

Referenced by filterM(), and filterS().

coef_out

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 102 of file fskmodem_float.c.

                                 {
    { 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, },
};

Referenced by filterL().