fskmodem_int.c File Reference

FSK Modulator/Demodulator. More...

#include "asterisk.h"
#include "asterisk/fskmodem.h"

Include dependency graph for fskmodem_int.c:

Go to the source code of this file.

Macros
#define	BWLIST   {75,800}
#define	FLIST   {1400,1800,1200,2200,1300,2100}
#define	IGET_SAMPLE   iget_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
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...
int	fskmodem_init (fsk_data *fskd)
static int	get_bit_raw (fsk_data *fskd, short *buffer, int *len)
static int	ibpdfilter (struct filter_struct *fs, int in)
static int	ibpfilter (struct filter_struct *fs, int in)
static int	idemodulator (fsk_data *fskd, int *retval, int x)
static int	iget_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_int.c.

Macro Definition Documentation

BWLIST

#define BWLIST   {75,800}

Definition at line 40 of file fskmodem_int.c.

FLIST

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

Definition at line 42 of file fskmodem_int.c.

IGET_SAMPLE

#define IGET_SAMPLE   iget_sample(&buffer, len)

Definition at line 58 of file fskmodem_int.c.

NBW

#define NBW   2

Definition at line 39 of file fskmodem_int.c.

NF

#define NF   6

Definition at line 41 of file fskmodem_int.c.

STATE_GET_BYTE

#define STATE_GET_BYTE   3

Definition at line 47 of file fskmodem_int.c.

STATE_SEARCH_STARTBIT

#define STATE_SEARCH_STARTBIT   0

Definition at line 44 of file fskmodem_int.c.

STATE_SEARCH_STARTBIT2

#define STATE_SEARCH_STARTBIT2   1

Definition at line 45 of file fskmodem_int.c.

STATE_SEARCH_STARTBIT3

#define STATE_SEARCH_STARTBIT3   2

Definition at line 46 of file fskmodem_int.c.

Function Documentation

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 222 of file fskmodem_int.c.

{
    int a;
    int i, j, n1, r;
    int samples = 0;
    int olen;
    int beginlen = *len;
    int beginlenx;
 
    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 */
        /* NOT USED
                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! */
        beginlenx = beginlen; /* just to avoid unused war warnings */
        if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
            return -1;
        samples++;
        for(;;) {
search_startbit2:
            if (*len <= 0) {
                fskd->state = STATE_SEARCH_STARTBIT2;
                return 0;
            }
            samples++;
            if (idemodulator(fskd, &fskd->xi2, IGET_SAMPLE))
                return -1;
#if 0
            printf("xi2 = %d ", fskd->xi2);
#endif
            if (fskd->xi2 < 512) {
                break;
            }
        }
search_startbit3:
        /* We await for 0.5 bits before using DPLL */
        i = fskd->ispb / 2;
        if (*len < i) {
            fskd->state = STATE_SEARCH_STARTBIT3;
            return 0;
        }
        for (; i > 0; i--) {
            if (idemodulator(fskd, &fskd->xi1, IGET_SAMPLE))
                return(-1);
#if 0
            printf("xi1 = %d ", fskd->xi1);
#endif
            samples++;
        }
 
        /* x1 must be negative (start bit confirmation) */
 
    } while (fskd->xi1 > 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->instop; 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;
}

References a, demodulator(), get_bit_raw(), GET_SAMPLE, idemodulator(), IGET_SAMPLE, fsk_data::instop, fsk_data::ispb, len(), fsk_data::nbit, fsk_data::nstop, fsk_data::parity, fsk_data::spb, fsk_data::state, STATE_GET_BYTE, STATE_SEARCH_STARTBIT, STATE_SEARCH_STARTBIT2, STATE_SEARCH_STARTBIT3, fsk_data::x1, fsk_data::x2, fsk_data::xi1, and fsk_data::xi2.

Referenced by callerid_feed(), callerid_feed_jp(), and tdd_feed().

fskmodem_init()

int fskmodem_init

(

fsk_data *

fskd

)

Definition at line 195 of file fskmodem_int.c.

{
    int i;
 
    fskd->space_filter.ip  = 0;
    fskd->mark_filter.ip   = 0;
    fskd->demod_filter.ip  = 0;
 
    for ( i = 0 ; i < 7 ; i++ ) {
        fskd->space_filter.icoefs[i] =
            coef_in[fskd->f_space_idx][fskd->bw][i] * 256;
        fskd->space_filter.ixv[i] = 0;;
        fskd->space_filter.iyv[i] = 0;;
 
        fskd->mark_filter.icoefs[i] =
            coef_in[fskd->f_mark_idx][fskd->bw][i] * 256;
        fskd->mark_filter.ixv[i] = 0;;
        fskd->mark_filter.iyv[i] = 0;;
 
        fskd->demod_filter.icoefs[i] =
            coef_out[fskd->bw][i] * 1024;
        fskd->demod_filter.ixv[i] = 0;;
        fskd->demod_filter.iyv[i] = 0;;
    }
    return 0;
}

References fsk_data::bw, coef_in, coef_out, fsk_data::demod_filter, fsk_data::f_mark_idx, fsk_data::f_space_idx, filter_struct::icoefs, filter_struct::ip, filter_struct::ixv, filter_struct::iyv, fsk_data::mark_filter, and fsk_data::space_filter.

Referenced by callerid_new(), and tdd_new().

get_bit_raw()

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

static

Definition at line 165 of file fskmodem_int.c.

{
    /* This function implements a DPLL to synchronize with the bits */
    int f;
 
    int ix;
    /* PLL coeffs are set up in callerid_new */
    for (f = 0;;) {
        if (idemodulator(fskd, &ix, IGET_SAMPLE)) return(-1);
        if ((ix * fskd->xi0) < 0) { /* Transicion */
            if (!f) {
                if (fskd->icont < (fskd->pllispb2)) {
                    fskd->icont += fskd->pllids;
                } else {
                    fskd->icont -= fskd->pllids;
                }
                f = 1;
            }
        }
        fskd->xi0 = ix;
        fskd->icont += 32;
        if (fskd->icont > fskd->pllispb) {
            fskd->icont -= fskd->pllispb;
            break;
        }
    }
    f = (ix > 0) ? 0x80 : 0;
    return f;
}

References fsk_data::icont, idemodulator(), IGET_SAMPLE, fsk_data::pllids, fsk_data::pllispb, fsk_data::pllispb2, and fsk_data::xi0.

Referenced by fsk_serial().

ibpdfilter()

static int ibpdfilter ( struct filter_struct *  fs, int  in  )

inlinestatic

Integer Pass Band demodulator filter

Definition at line 95 of file fskmodem_int.c.

{
    int i,j;
    int s;
    int64_t s_interim;
 
    /* integer filter */
    s =  in * fs->icoefs[0];
    fs->ixv[(fs->ip + 6) & 7] = s;
 
    s =      (fs->ixv[fs->ip]           + fs->ixv[(fs->ip + 6) & 7]) +
        6  * (fs->ixv[(fs->ip + 1) & 7] + fs->ixv[(fs->ip + 5) & 7]) +
        15 * (fs->ixv[(fs->ip + 2) & 7] + fs->ixv[(fs->ip + 4) & 7]) +
        20 *  fs->ixv[(fs->ip + 3) & 7];
 
    for (i = 1, j = fs->ip; i < 7; i++, j++) {
        /* Promote operation to 64 bit to prevent overflow that occurred in 32 bit) */
        s_interim = (int64_t)(fs->iyv[j & 7]) *
                (int64_t)(fs->icoefs[i]) /
                (int64_t)(1024);
        s += (int) s_interim;
    }
    fs->iyv[j & 7] = s;
    fs->ip++;
    fs->ip &= 7;
    return s;
}

References filter_struct::icoefs, in, filter_struct::ip, filter_struct::ixv, and filter_struct::iyv.

Referenced by idemodulator().

ibpfilter()

static int ibpfilter ( struct filter_struct *  fs, int  in  )

inlinestatic

Integer Band Pass filter

Definition at line 124 of file fskmodem_int.c.

{
    int i, j;
    int s;
    int64_t s_interim;
 
    /* integer filter */
    s =  in * fs->icoefs[0] / 256;
    fs->ixv[(fs->ip + 6) & 7] = s;
 
    s = (fs->ixv[(fs->ip + 6) & 7] - fs->ixv[fs->ip])
        + 3 * (fs->ixv[(fs->ip + 2) & 7] - fs->ixv[(fs->ip + 4) & 7]);
 
    for (i = 1, j = fs->ip; i < 7; i++, j++) {
        s_interim = (int64_t)(fs->iyv[j & 7]) *
                (int64_t)(fs->icoefs[i]) /
                (int64_t)(256);
        s += (int) s_interim;
    }
    fs->iyv[j & 7] = s;
    fs->ip++;
    fs->ip &= 7;
    return s;
}

References filter_struct::icoefs, in, filter_struct::ip, filter_struct::ixv, and filter_struct::iyv.

Referenced by idemodulator().

idemodulator()

static int idemodulator ( fsk_data *  fskd, int *  retval, int  x  )

inlinestatic

Definition at line 149 of file fskmodem_int.c.

{
    int is, im, id;
    int ilin2;
 
    is = ibpfilter(&fskd->space_filter, x);
    im = ibpfilter(&fskd->mark_filter, x);
 
    ilin2 = ((im * im) - (is * is)) / (256 * 256);
 
    id = ibpdfilter(&fskd->demod_filter, ilin2);
 
    *retval = id;
    return 0;
}

References fsk_data::demod_filter, ibpdfilter(), ibpfilter(), id, fsk_data::mark_filter, retval, and fsk_data::space_filter.

Referenced by fsk_serial(), and get_bit_raw().

iget_sample()

static int iget_sample ( short **  buffer, int *  len  )

inlinestatic

Definition at line 49 of file fskmodem_int.c.

{
    int retval;
    retval = (int) **buffer;
    (*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 66 of file fskmodem_int.c.

Referenced by fskmodem_init().

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 88 of file fskmodem_int.c.

Referenced by fskmodem_init().