forked from EliasOenal/multimon-ng
-
Notifications
You must be signed in to change notification settings - Fork 0
/
demod_eas.c
386 lines (338 loc) · 13.5 KB
/
demod_eas.c
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
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
/*
* demod_eas.c -- Emergency Alert System demodulator
*
* See http://www.nws.noaa.gov/nwr/nwrsame.htm
*
* Copyright (C) 2000
* A. Maitland Bottoms <[email protected]>
*
* Licensed under same terms and based upon the
* demod_afsk12.c -- 1200 baud AFSK demodulator
*
* Copyright (C) 1996
* Thomas Sailer ([email protected], [email protected])
*
* 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
* Bit Parameters
* The following definitions of a bit are based on a bit period equaling
* 1920 microseconds (± one microsecond).
* a.) The speed is 520.83 bits per second
* b.) Logic zero is 1562.5 Hz.
* c.) Logic one is 2083.3 Hz
*
* preamble is 0xAB sent on wire as LSB first
* 11010101
* start of message header begins with ZCZC
0101101011000010
* message ends with NNNN
* 01110010
*/
#define FREQ_MARK 2083.3 // binary 1 freq, in Hz
#define FREQ_SPACE 1562.5 // binary 0 freq, in Hz
#define FREQ_SAMP 22050 // req'd input sampling rate, in Hz
#define BAUD 520.83 // symbol rate, in Hz
#define PREAMBLE ((unsigned char)0xAB) // preamble byte, MSB first
#define HEADER_BEGIN "ZCZC" // message begin
#define EOM "NNNN" // message end
// Storage options
#define MAX_MSG_LEN 268 // maximum length of EAS message
#define MAX_HEADER_LEN 4 // header length (begin vs end)
#define MAX_STORE_MSG 3 // # of msgs to store and compare
// Signal processing options
#define SUBSAMP 2 // downsampling factor
#define DLL_GAIN_UNSYNC 1/2.0 // DLL gain when unsynchronized
#define DLL_GAIN_SYNC 1/2.0 // DLL gain when synchronized
#define DLL_MAX_INC 8192 // max DLL per-sample shift
#define INTEGRATOR_MAXVAL 10 // sampling integrator bounds
#define MIN_IDENTICAL_MSGS 2 // # of msgs which must be identical
/* ---------------------------------------------------------------------- */
#define CORRLEN ((int)(FREQ_SAMP/BAUD))
#define SPHASEINC (0x10000u*BAUD*SUBSAMP/FREQ_SAMP)
static float eascorr_mark_i[CORRLEN];
static float eascorr_mark_q[CORRLEN];
static float eascorr_space_i[CORRLEN];
static float eascorr_space_q[CORRLEN];
#define MAX(a,b) (((a)>(b))?(a):(b))
#define MIN(a,b) (((a)<(b))?(a):(b))
/* ---------------------------------------------------------------------- */
static void eas_init(struct demod_state *s)
{
float f;
int i;
memset(&s->l1.eas, 0, sizeof(s->l1.eas));
memset(&s->l2.eas, 0, sizeof(s->l2.eas));
for (f = 0, i = 0; i < CORRLEN; i++) {
eascorr_mark_i[i] = cos(f);
eascorr_mark_q[i] = sin(f);
f += 2.0*M_PI*FREQ_MARK/FREQ_SAMP;
}
for (f = 0, i = 0; i < CORRLEN; i++) {
eascorr_space_i[i] = cos(f);
eascorr_space_q[i] = sin(f);
f += 2.0*M_PI*FREQ_SPACE/FREQ_SAMP;
}
}
/* ---------------------------------------------------------------------- */
static char eas_allowed(char data)
{
// determine if a character is allowed in an EAS frame
// returns true if it is
// high-byte ASCII characters are forbidden
if (data & 0x80)
return 0;
if (data == 13 || data == 10)
// LF and CR are allowed
return 1;
if (data >= 32 || data <= 126)
// These text and punctuation characters are allowed
return 1;
// all other characters forbidden
return 0;
}
static void eas_frame(struct demod_state *s, char data)
{
int i,j = 0;
char * ptr = 0;
if (data)
{
// if we're idle, now we're looking for a header
if (s->l2.eas.state == EAS_L2_IDLE)
s->l2.eas.state = EAS_L2_HEADER_SEARCH;
if (s->l2.eas.state == EAS_L2_HEADER_SEARCH &&
s->l2.eas.headlen < MAX_HEADER_LEN)
{
// put it in the header buffer if we have room
s->l2.eas.head_buf[s->l2.eas.headlen] = data;
s->l2.eas.headlen++;
}
if (s->l2.eas.state == EAS_L2_HEADER_SEARCH &&
s->l2.eas.headlen >= MAX_HEADER_LEN)
{
// test first 4 bytes to see if they are a header
if (!strncmp(s->l2.eas.head_buf, HEADER_BEGIN, s->l2.eas.headlen))
// have found header. keep reading
s->l2.eas.state = EAS_L2_READING_MESSAGE;
else if (!strncmp(s->l2.eas.head_buf, EOM, s->l2.eas.headlen))
// have found EOM
s->l2.eas.state = EAS_L2_READING_EOM;
else
{
// not valid, abort and clear buffer
s->l2.eas.state = EAS_L2_IDLE;
s->l2.eas.headlen = 0;
}
}
else if (s->l2.eas.state == EAS_L2_READING_MESSAGE &&
s->l2.eas.msglen <= MAX_MSG_LEN)
{
// space is available; store in message buffer
s->l2.eas.msg_buf[s->l2.eas.msgno][s->l2.eas.msglen] = data;
s->l2.eas.msglen++;
}
}
else
{
// the header has ended
// fill the rest of the buffer will NULs
memset(&s->l2.eas.msg_buf[s->l2.eas.msgno][s->l2.eas.msglen], '\0',
MAX_MSG_LEN - s->l2.eas.msglen);
//s->l2.eas.msg_buf[s->l2.eas.msgno][s->l2.eas.msglen] = '\0';
if (s->l2.eas.state == EAS_L2_READING_MESSAGE)
{
// All EAS messages should end in a minus sign ("-")
// trim any trailing characters
ptr = strrchr(&s->l2.eas.msg_buf[s->l2.eas.msgno], '-');
if (ptr)
{
// found. make the next character zero
*(ptr+1) = '\0';
}
// display message if verbosity permits
verbprintf(7, "\n");
verbprintf(1, "%s (part): %s%s\n", s->dem_par->name, HEADER_BEGIN,
s->l2.eas.msg_buf[s->l2.eas.msgno]);
// increment message number
s->l2.eas.msgno += 1;
if (s->l2.eas.msgno >= MAX_STORE_MSG)
s->l2.eas.msgno = 0;
// check for message agreement; 2 of 3 must agree
for (i = 0; i < MAX_STORE_MSG; i++)
{
// if this message is empty or matches the one we've just
// alerted the user to, ignore it.
if (s->l2.eas.msg_buf[i][0] == '\0' ||
!strncmp(s->l2.eas.last_message,
s->l2.eas.msg_buf[i], MAX_MSG_LEN))
continue;
for (j = i+1; j < MAX_STORE_MSG; j++)
{
// test if messages are identical and not a dupe of the
// last message
if (!strncmp(s->l2.eas.msg_buf[i],
s->l2.eas.msg_buf[j],
MAX_MSG_LEN))
{
// store message to prevent dupes
strncpy(s->l2.eas.last_message, s->l2.eas.msg_buf[j],
MAX_MSG_LEN);
// raise the alert and discontinue processing
verbprintf(7, "\n");
verbprintf(0, "%s: %s%s\n", s->dem_par->name, HEADER_BEGIN,
s->l2.eas.last_message);
i = MAX_STORE_MSG;
break;
}
}
}
}
else if (s->l2.eas.state == EAS_L2_READING_EOM)
{
// raise the EOM
verbprintf(0, "%s: %s\n", s->dem_par->name, EOM);
}
// go back to idle
s->l2.eas.state = EAS_L2_IDLE;
s->l2.eas.msglen = 0;
s->l2.eas.headlen = 0;
}
}
static void eas_demod(struct demod_state *s, buffer_t buffer, int length)
{
float f;
unsigned char curbit;
float dll_gain;
if (s->l1.eas.subsamp) {
int numfill = SUBSAMP - s->l1.eas.subsamp;
if (length < numfill) {
s->l1.eas.subsamp += length;
return;
}
buffer.fbuffer += numfill;
length -= numfill;
s->l1.eas.subsamp = 0;
}
// We use a sliding window correlator which advances by SUBSAMP
// each time. One correlator sample is output for each SUBSAMP symbols
for (; length >= SUBSAMP; length -= SUBSAMP, buffer.fbuffer += SUBSAMP) {
f = fsqr(mac(buffer.fbuffer, eascorr_mark_i, CORRLEN)) +
fsqr(mac(buffer.fbuffer, eascorr_mark_q, CORRLEN)) -
fsqr(mac(buffer.fbuffer, eascorr_space_i, CORRLEN)) -
fsqr(mac(buffer.fbuffer, eascorr_space_q, CORRLEN));
// f > 0 if a mark (wireline 1) is detected
// keep the last few correlator samples in s->l1.eas.dcd_shreg
// when we've synchronized to the bit transitions, the dcd_shreg
// will have (nearly) a single value per symbol
s->l1.eas.dcd_shreg <<= 1;
s->l1.eas.dcd_shreg |= (f > 0);
// the integrator is positive for 1 bits, and negative for 0 bits
if (f > 0 && (s->l1.eas.dcd_integrator < INTEGRATOR_MAXVAL))
{
s->l1.eas.dcd_integrator += 1;
}
else if (f < 0 && s->l1.eas.dcd_integrator > -INTEGRATOR_MAXVAL)
{
s->l1.eas.dcd_integrator -= 1;
}
verbprintf(9, "%c", '0'+(s->l1.afsk12.dcd_shreg & 1));
/*
* check if transition occurred on time
*/
if (s->l2.eas.state != EAS_L2_IDLE)
dll_gain = DLL_GAIN_SYNC;
else
dll_gain = DLL_GAIN_UNSYNC;
// want transitions to take place near 0 phase
if ((s->l1.eas.dcd_shreg ^ (s->l1.eas.dcd_shreg >> 1)) & 1) {
if (s->l1.eas.sphase < (0x8000u-(SPHASEINC/8)))
{
// before center; check for decrement
if (s->l1.eas.sphase > (SPHASEINC/2))
{
s->l1.eas.sphase -= MIN((int)((s->l1.eas.sphase)*dll_gain), DLL_MAX_INC);
verbprintf(10,"|-%d|", MIN((int)((s->l1.eas.sphase)*dll_gain), DLL_MAX_INC));
}
}
else
{
// after center; check for increment
if (s->l1.eas.sphase < (0x10000u - SPHASEINC/2))
{
s->l1.eas.sphase += MIN((int)((0x10000u - s->l1.eas.sphase)*
dll_gain), DLL_MAX_INC);
verbprintf(10,"|+%d|", MIN((int)((0x10000u - s->l1.eas.sphase)*
dll_gain), DLL_MAX_INC));
}
}
}
s->l1.eas.sphase += SPHASEINC;
if (s->l1.eas.sphase >= 0x10000u) {
// end of bit period.
s->l1.eas.sphase = 1; //was &= 0xffffu;
s->l1.eas.lasts >>= 1;
// if at least half of the values in the integrator are 1,
// declare a 1 received
s->l1.afsk12.lasts |= ((s->l1.eas.dcd_integrator >= 0) << 7) & 0x80u;
curbit = (s->l1.eas.lasts >> 7) & 0x1u;
verbprintf(9, " ");
verbprintf(7, "%c", '0'+curbit);
// check for sync sequence
// do not resync when we're reading a message!
if (s->l1.eas.lasts == PREAMBLE
&& s->l2.eas.state != EAS_L2_READING_MESSAGE)
{
// sync found; declare current offset as byte sync
s->l1.eas.state = EAS_L1_SYNC;
s->l1.eas.byte_counter = 0;
verbprintf(9, " sync");
}
else if (s->l1.eas.state == EAS_L1_SYNC)
{
s->l1.eas.byte_counter++;
if (s->l1.eas.byte_counter == 8)
{
// lasts now contains one full byte
if (eas_allowed((char) s->l1.eas.lasts))
{
eas_frame(s, (char) s->l1.eas.lasts);
verbprintf(9, " %c", (char)s->l1.eas.lasts);
}
else
{
// character not valid. we have lost our sync
s->l1.eas.state = EAS_L1_IDLE;
eas_frame(s, 0x00);
}
s->l1.eas.byte_counter = 0;
}
}
verbprintf(9, "\n");
}
}
s->l1.eas.subsamp = length;
}
/* ---------------------------------------------------------------------- */
const struct demod_param demod_eas = {
"EAS", true, FREQ_SAMP, CORRLEN, eas_init, eas_demod, NULL
};
/* ---------------------------------------------------------------------- */