util/spkmodem_recv/spkmodem-recv.c

   1 /* spkmodem-recv.c - decode spkmodem signals */
   2 /*
   3  *  Copyright (C) 2013  Vladimir 'phcoder' Serbinenko
   4  *
   5  *  spkmodem-recv is free software: you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation, either version 2 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  spkmodem-recv is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  */
  15
  16 #include <stdio.h>
  17 #include <stdlib.h>
  18 #include <string.h>
  19
  20 /* Compilation:  gcc -o spkmodem-recv spkmodem-recv  */
  21 /* Usage: parecord --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv */
  22
  23 #define SAMPLES_PER_TRAME 240
  24 #define FREQ_SEP_MIN 5
  25 #define FREQ_SEP_MAX 15
  26 #define FREQ_DATA_MIN 15
  27 #define FREQ_DATA_THRESHOLD 25
  28 #define FREQ_DATA_MAX 60
  29 #define THRESHOLD 500
  30
  31 #define DEBUG 0
  32 #define FLUSH_TIMEOUT 1
  33
  34 static signed short trame[2 * SAMPLES_PER_TRAME];
  35 static signed short pulse[2 * SAMPLES_PER_TRAME];
  36 static int ringpos = 0;
  37 static int pos, f1, f2;
  38 static int amplitude = 0;
  39 static int lp = 0;
  40
  41 static void
  42 read_sample (void)
  43 {
  44   amplitude -= abs (trame[ringpos]);
  45   f1 -= pulse[ringpos];
  46   f1 += pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
  47   f2 -= pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
  48   fread (trame + ringpos, 1, sizeof (trame[0]), stdin);
  49   amplitude += abs (trame[ringpos]);
  50
  51   if (pos ? (trame[ringpos] < -THRESHOLD)
  52       : (trame[ringpos] > +THRESHOLD))
  53     {
  54       pulse[ringpos] = 1;
  55       pos = !pos;
  56       f2++;
  57     }
  58   else
  59     pulse[ringpos] = 0;
  60   ringpos++;
  61   ringpos %= 2 * SAMPLES_PER_TRAME;
  62   lp++;
  63 }
  64
  65 int
  66 main ()
  67 {
  68   int bitn = 7;
  69   char c = 0;
  70   int i;
  71   int llp = 0;
  72   while (!feof (stdin))
  73     {
  74       if (lp > 3 * SAMPLES_PER_TRAME)
  75         {
  76           bitn = 7;
  77           c = 0;
  78           lp = 0;
  79           llp++;
  80         }
  81       if (llp == FLUSH_TIMEOUT)
  82         fflush (stdout);
  83       if (f2 > FREQ_SEP_MIN && f2 < FREQ_SEP_MAX
  84           && f1 > FREQ_DATA_MIN && f1 < FREQ_DATA_MAX)
  85         {
  86 #if DEBUG
  87           printf ("%d %d %d @%d\n", f1, f2, FREQ_DATA_THRESHOLD,
  88                   ftell (stdin) - sizeof (trame));
  89 #endif
  90           if (f1 < FREQ_DATA_THRESHOLD)
  91             c |= (1 << bitn);
  92           bitn--;
  93           if (bitn < 0)
  94             {
  95 #if DEBUG
  96               printf ("<%c, %x>", c, c);
  97 #else
  98               printf ("%c", c);
  99 #endif
 100               bitn = 7;
 101               c = 0;
 102             }
 103           lp = 0;
 104           llp = 0;
 105           for (i = 0; i < SAMPLES_PER_TRAME; i++)
 106             read_sample ();
 107           continue;
 108         }
 109       read_sample ();
 110     }
 111   return 0;
 112 }