113 lines
2.5 KiB
C
113 lines
2.5 KiB
C
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/* spkmodem-recv.c - decode spkmodem signals */
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/*
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* Copyright (C) 2013 Vladimir 'phcoder' Serbinenko
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*
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* spkmodem-recv is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 2 of the License, or
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* (at your option) any later version.
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*
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* spkmodem-recv is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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/* Compilation: gcc -o spkmodem-recv spkmodem-recv */
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/* Usage: parec --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv */
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#define SAMPLES_PER_TRAME 240
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#define FREQ_SEP_MIN 5
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#define FREQ_SEP_MAX 15
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#define FREQ_DATA_MIN 15
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#define FREQ_DATA_THRESHOLD 25
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#define FREQ_DATA_MAX 60
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#define THRESHOLD 500
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#define DEBUG 0
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#define FLUSH_TIMEOUT 1
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static signed short trame[2 * SAMPLES_PER_TRAME];
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static signed short pulse[2 * SAMPLES_PER_TRAME];
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static int ringpos = 0;
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static int pos, f1, f2;
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static int amplitude = 0;
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static int lp = 0;
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static void
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read_sample (void)
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{
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amplitude -= abs (trame[ringpos]);
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f1 -= pulse[ringpos];
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f1 += pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
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f2 -= pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
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fread (trame + ringpos, 1, sizeof (trame[0]), stdin);
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amplitude += abs (trame[ringpos]);
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if (pos ? (trame[ringpos] < -THRESHOLD)
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: (trame[ringpos] > +THRESHOLD))
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{
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pulse[ringpos] = 1;
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pos = !pos;
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f2++;
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}
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else
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pulse[ringpos] = 0;
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ringpos++;
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ringpos %= 2 * SAMPLES_PER_TRAME;
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lp++;
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}
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int
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main ()
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{
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int bitn = 7;
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char c = 0;
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int i;
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int llp = 0;
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while (!feof (stdin))
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{
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if (lp > 3 * SAMPLES_PER_TRAME)
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{
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bitn = 7;
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c = 0;
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lp = 0;
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llp++;
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}
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if (llp == FLUSH_TIMEOUT)
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fflush (stdout);
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if (f2 > FREQ_SEP_MIN && f2 < FREQ_SEP_MAX
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&& f1 > FREQ_DATA_MIN && f1 < FREQ_DATA_MAX)
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{
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#if DEBUG
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printf ("%d %d %d @%d\n", f1, f2, FREQ_DATA_THRESHOLD,
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ftell (stdin) - sizeof (trame));
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#endif
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if (f1 < FREQ_DATA_THRESHOLD)
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c |= (1 << bitn);
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bitn--;
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if (bitn < 0)
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{
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#if DEBUG
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printf ("<%c, %x>", c, c);
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#else
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printf ("%c", c);
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#endif
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bitn = 7;
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c = 0;
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}
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lp = 0;
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llp = 0;
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for (i = 0; i < SAMPLES_PER_TRAME; i++)
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read_sample ();
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continue;
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}
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read_sample ();
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}
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return 0;
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}
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