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/*
* demod_poc24.c -- 2400 baud POCSAG demodulator
*
* Copyright (C) 1996
* Thomas Sailer (sailer@ife.ee.ethz.ch, hb9jnx@hb9w.che.eu)
*
* POCSAG (Post Office Code Standard Advisory Group)
* Radio Paging Decoder
*
* 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 2400
#define FILTLEN 1
/* ---------------------------------------------------------------------- */
#define SPHASEINC (0x10000u*BAUD/FREQ_SAMP)
/* ---------------------------------------------------------------------- */
static void poc24_init(struct demod_state *s)
{
pocsag_init(s);
memset(&s->l1.poc24, 0, sizeof(s->l1.poc24));
}
/* ---------------------------------------------------------------------- */
static void poc24_demod(struct demod_state *s, float *buffer, int length)
{
for (; length > 0; length--, buffer++) {
s->l1.poc24.dcd_shreg <<= 1;
s->l1.poc24.dcd_shreg |= ((*buffer) > 0);
verbprintf(10, "%c", '0'+(s->l1.poc24.dcd_shreg & 1));
/*
* check if transition
*/
if ((s->l1.poc24.dcd_shreg ^ (s->l1.poc24.dcd_shreg >> 1)) & 1) {
if (s->l1.poc24.sphase < (0x8000u-(SPHASEINC/2)))
s->l1.poc24.sphase += SPHASEINC/8;
else
s->l1.poc24.sphase -= SPHASEINC/8;
}
s->l1.poc24.sphase += SPHASEINC;
if (s->l1.poc24.sphase >= 0x10000u) {
s->l1.poc24.sphase &= 0xffffu;
pocsag_rxbit(s, s->l1.poc24.dcd_shreg & 1);
}
}
}
/* ---------------------------------------------------------------------- */
const struct demod_param demod_poc24 = {
"POCSAG2400", FREQ_SAMP, FILTLEN, poc24_init, poc24_demod
};
/* ---------------------------------------------------------------------- */
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