/* spkmodem-recv.c - decode spkmodem signals */ /* * Copyright (C) 2013 Vladimir 'phcoder' Serbinenko * * spkmodem-recv 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. * * spkmodem-recv 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. */ #include <stdio.h> #include <stdlib.h> #include <string.h> /* Compilation: gcc -o spkmodem-recv spkmodem-recv */ /* Usage: parec --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv */ #define SAMPLES_PER_TRAME 240 #define FREQ_SEP_MIN 5 #define FREQ_SEP_MAX 15 #define FREQ_DATA_MIN 15 #define FREQ_DATA_THRESHOLD 25 #define FREQ_DATA_MAX 60 #define THRESHOLD 500 #define DEBUG 0 #define FLUSH_TIMEOUT 1 static signed short trame[2 * SAMPLES_PER_TRAME]; static signed short pulse[2 * SAMPLES_PER_TRAME]; static int ringpos = 0; static int pos, f1, f2; static int amplitude = 0; static int lp = 0; static void read_sample (void) { amplitude -= abs (trame[ringpos]); f1 -= pulse[ringpos]; f1 += pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)]; f2 -= pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)]; fread (trame + ringpos, 1, sizeof (trame[0]), stdin); amplitude += abs (trame[ringpos]); if (pos ? (trame[ringpos] < -THRESHOLD) : (trame[ringpos] > +THRESHOLD)) { pulse[ringpos] = 1; pos = !pos; f2++; } else pulse[ringpos] = 0; ringpos++; ringpos %= 2 * SAMPLES_PER_TRAME; lp++; } int main () { int bitn = 7; char c = 0; int i; int llp = 0; while (!feof (stdin)) { if (lp > 3 * SAMPLES_PER_TRAME) { bitn = 7; c = 0; lp = 0; llp++; } if (llp == FLUSH_TIMEOUT) fflush (stdout); if (f2 > FREQ_SEP_MIN && f2 < FREQ_SEP_MAX && f1 > FREQ_DATA_MIN && f1 < FREQ_DATA_MAX) { #if DEBUG printf ("%d %d %d @%d\n", f1, f2, FREQ_DATA_THRESHOLD, ftell (stdin) - sizeof (trame)); #endif if (f1 < FREQ_DATA_THRESHOLD) c |= (1 << bitn); bitn--; if (bitn < 0) { #if DEBUG printf ("<%c, %x>", c, c); #else printf ("%c", c); #endif bitn = 7; c = 0; } lp = 0; llp = 0; for (i = 0; i < SAMPLES_PER_TRAME; i++) read_sample (); continue; } read_sample (); } return 0; }