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/*
* demod_fsk96.c -- FSK 9600 baud demodulator (G3RUH)
*
* 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>
/* ---------------------------------------------------------------------- */
#define FREQ_SAMP 22050
#define BAUD 9600
/* ---------------------------------------------------------------------- */
#define DESCRAM_TAP1 0x20000
#define DESCRAM_TAP2 0x01000
#define DESCRAM_TAP3 0x00001
#define DESCRAM_TAPSH1 17
#define DESCRAM_TAPSH2 12
#define DESCRAM_TAPSH3 0
#define SCRAM_TAP1 0x20000 /* X^17 */
#define SCRAM_TAPN 0x00021 /* X^0+X^5 */
/* --------------------------------------------------------------------- */
#define FILTLEN 24
#define UPSAMP 3
static const float inp_filt[3][24] = {
{ 0.000440, -0.001198, -0.000493, 0.003648,
-0.000630, -0.008433, 0.005567, 0.015557,
-0.019931, -0.026514, 0.079822, 0.181779,
0.124956, -0.002471, -0.032062, 0.008024,
0.012568, -0.006559, -0.004235, 0.003711,
0.000909, -0.001520, -0.000018, 0.000709},
{ 0.000686, -0.000618, -0.001332, 0.002494,
0.002258, -0.007308, -0.001538, 0.016708,
-0.004897, -0.035748, 0.034724, 0.161417,
0.161417, 0.034724, -0.035748, -0.004897,
0.016708, -0.001538, -0.007308, 0.002258,
0.002494, -0.001332, -0.000618, 0.000686},
{ 0.000709, -0.000018, -0.001520, 0.000909,
0.003711, -0.004235, -0.006559, 0.012568,
0.008024, -0.032062, -0.002471, 0.124956,
0.181779, 0.079822, -0.026514, -0.019931,
0.015557, 0.005567, -0.008433, -0.000630,
0.003648, -0.000493, -0.001198, 0.000440}
};
#define SPHASEINC (0x10000u*BAUD/FREQ_SAMP/UPSAMP)
/* ---------------------------------------------------------------------- */
static void fsk96_init(struct demod_state *s)
{
hdlc_init(s);
memset(&s->l1.fsk96, 0, sizeof(s->l1.fsk96));
}
/* ---------------------------------------------------------------------- */
static void fsk96_demod(struct demod_state *s, buffer_t buffer, int length)
{
float f;
unsigned char curbit;
int i;
unsigned int descx;
for (; length > 0; length--, buffer.fbuffer++) {
for (i = 0; i < UPSAMP; i++) {
f = mac(buffer.fbuffer, inp_filt[i], FILTLEN);
s->l1.fsk96.dcd_shreg <<= 1;
s->l1.fsk96.dcd_shreg |= (f > 0);
verbprintf(10, "%c", '0'+(s->l1.fsk96.dcd_shreg & 1));
/*
* check if transition
*/
if ((s->l1.fsk96.dcd_shreg ^ (s->l1.fsk96.dcd_shreg >> 1)) & 1) {
if (s->l1.fsk96.sphase < (0x8000u-(SPHASEINC/2)))
s->l1.fsk96.sphase += SPHASEINC/8;
else
s->l1.fsk96.sphase -= SPHASEINC/8;
}
s->l1.fsk96.sphase += SPHASEINC;
if (s->l1.fsk96.sphase >= 0x10000u) {
s->l1.fsk96.sphase &= 0xffffu;
s->l1.fsk96.descram <<= 1;
s->l1.fsk96.descram |= s->l1.fsk96.dcd_shreg & 1;
descx = s->l1.fsk96.descram ^ (s->l1.fsk96.descram >> 1);
curbit = ((descx >> DESCRAM_TAPSH1) ^ (descx >> DESCRAM_TAPSH2) ^
(descx >> DESCRAM_TAPSH3) ^ 1) & 1;
verbprintf(9, " %c ", '0'+curbit);
hdlc_rxbit(s, curbit);
}
}
}
}
/* ---------------------------------------------------------------------- */
const struct demod_param demod_fsk9600 = {
"FSK9600", true, FREQ_SAMP, FILTLEN, fsk96_init, fsk96_demod, NULL
};
/* ---------------------------------------------------------------------- */
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