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/*
* demod_afsk24.c -- 2400 baud AFSK demodulator
*
* Copyright (C) 1996
* Thomas Sailer (sailer@ife.ee.ethz.ch, hb9jnx@hb9w.che.eu)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/* ---------------------------------------------------------------------- */
#include "multimon.h"
#include "filter.h"
#include <math.h>
#include <string.h>
/* ---------------------------------------------------------------------- */
/*
* Standard TCM3105 clock frequency: 4.4336MHz
* Xtal used: 8 MHz
* Ratio: 1.8044
* Mark frequency: 3970 Hz
* Space frequency: 2165 Hz
*/
#define FREQ_MARK 3970
#define FREQ_SPACE 2165
#define FREQ_SAMP 22050
#define BAUD 2400
/* ---------------------------------------------------------------------- */
#define CORRLEN (2*(int)(FREQ_SAMP/BAUD))
#define SPHASEINC (0x10000u*BAUD/FREQ_SAMP)
static float corr_mark_i[CORRLEN];
static float corr_mark_q[CORRLEN];
static float corr_space_i[CORRLEN];
static float corr_space_q[CORRLEN];
/* ---------------------------------------------------------------------- */
static void afsk24_init(struct demod_state *s)
{
float f;
int i;
hdlc_init(s);
memset(&s->l1.afsk24, 0, sizeof(s->l1.afsk24));
for (f = 0, i = 0; i < CORRLEN; i++) {
corr_mark_i[i] = cos(f);
corr_mark_q[i] = sin(f);
f += 2.0*M_PI*FREQ_MARK/FREQ_SAMP;
}
for (f = 0, i = 0; i < CORRLEN; i++) {
corr_space_i[i] = cos(f);
corr_space_q[i] = sin(f);
f += 2.0*M_PI*FREQ_SPACE/FREQ_SAMP;
}
for (i = 0; i < CORRLEN; i++) {
f = 0.54 - 0.46*cos(2*M_PI*i/(float)(CORRLEN-1));
corr_mark_i[i] *= f;
corr_mark_q[i] *= f;
corr_space_i[i] *= f;
corr_space_q[i] *= f;
}
}
/* ---------------------------------------------------------------------- */
static void afsk24_demod(struct demod_state *s, float *buffer, int length)
{
float f;
unsigned char curbit;
for (; length > 0; length--, buffer++) {
f = fsqr(mac(buffer, corr_mark_i, CORRLEN)) +
fsqr(mac(buffer, corr_mark_q, CORRLEN)) -
fsqr(mac(buffer, corr_space_i, CORRLEN)) -
fsqr(mac(buffer, corr_space_q, CORRLEN));
s->l1.afsk24.dcd_shreg <<= 1;
s->l1.afsk24.dcd_shreg |= (f > 0);
verbprintf(10, "%c", '0'+(s->l1.afsk24.dcd_shreg & 1));
/*
* check if transition
*/
if ((s->l1.afsk24.dcd_shreg ^ (s->l1.afsk24.dcd_shreg >> 1)) & 1) {
if (s->l1.afsk24.sphase < (0x8000u-(SPHASEINC/2)))
s->l1.afsk24.sphase += SPHASEINC/8;
else
s->l1.afsk24.sphase -= SPHASEINC/8;
}
s->l1.afsk24.sphase += SPHASEINC;
if (s->l1.afsk24.sphase >= 0x10000u) {
s->l1.afsk24.sphase &= 0xffffu;
s->l1.afsk24.lasts <<= 1;
s->l1.afsk24.lasts |= s->l1.afsk24.dcd_shreg & 1;
curbit = (s->l1.afsk24.lasts ^
(s->l1.afsk24.lasts >> 1) ^ 1) & 1;
verbprintf(9, " %c ", '0'+curbit);
hdlc_rxbit(s, curbit);
}
}
}
/* ---------------------------------------------------------------------- */
const struct demod_param demod_afsk2400 = {
"AFSK2400", FREQ_SAMP, CORRLEN, afsk24_init, afsk24_demod
};
/* ---------------------------------------------------------------------- */
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