File: demod_poc5.c

package info (click to toggle)
multimon 1.0-7.1
  • links: PTS
  • area: main
  • in suites: bullseye, buster, sid, stretch
  • size: 576 kB
  • ctags: 924
  • sloc: ansic: 8,144; makefile: 233; perl: 41
file content (92 lines) | stat: -rw-r--r-- 2,857 bytes parent folder | download | duplicates (7)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
/*
 *      demod_poc5.c -- 512 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       512
#define SUBSAMP    5
#define FILTLEN    1

/* ---------------------------------------------------------------------- */

#define SPHASEINC (0x10000u*BAUD*SUBSAMP/FREQ_SAMP)

/* ---------------------------------------------------------------------- */
	
static void poc5_init(struct demod_state *s)
{
	pocsag_init(s);
	memset(&s->l1.poc5, 0, sizeof(s->l1.poc5));
}

/* ---------------------------------------------------------------------- */

static void poc5_demod(struct demod_state *s, float *buffer, int length)
{
	if (s->l1.poc5.subsamp) {
		int numfill = SUBSAMP - s->l1.poc5.subsamp;
		if (length < numfill) {
			s->l1.poc5.subsamp += length;
			return;
		}
		buffer += numfill;
		length -= numfill;
		s->l1.poc5.subsamp = 0;
	}
	for (; length >= SUBSAMP; length -= SUBSAMP, buffer += SUBSAMP) {
		s->l1.poc5.dcd_shreg <<= 1;
		s->l1.poc5.dcd_shreg |= ((*buffer) > 0);
		verbprintf(10, "%c", '0'+(s->l1.poc5.dcd_shreg & 1));
		/*
		 * check if transition
		 */
		if ((s->l1.poc5.dcd_shreg ^ (s->l1.poc5.dcd_shreg >> 1)) & 1) {
			if (s->l1.poc5.sphase < (0x8000u-(SPHASEINC/2)))
				s->l1.poc5.sphase += SPHASEINC/8;
			else
				s->l1.poc5.sphase -= SPHASEINC/8;
		}
		s->l1.poc5.sphase += SPHASEINC;
		if (s->l1.poc5.sphase >= 0x10000u) {
			s->l1.poc5.sphase &= 0xffffu;
			pocsag_rxbit(s, s->l1.poc5.dcd_shreg & 1);
		}
	}
	s->l1.poc5.subsamp = length;
}

/* ---------------------------------------------------------------------- */

const struct demod_param demod_poc5 = {
	"POCSAG512", FREQ_SAMP, FILTLEN, poc5_init, poc5_demod
};

/* ---------------------------------------------------------------------- */