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:

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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. More...
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]. More...
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]. More...

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, fsk_data::pcola, and retval.

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 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;
}

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;
};

References 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.

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.

Referenced by filterL().