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/* spkmodem-recv.c - decode spkmodem signals */
/*
* Copyright (C) 2013 Free Software Foundation, Inc.
*
* 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.
*
* You should have received a copy of the GNU General Public License
* along with spkmodem-recv. If not, see <http://www.gnu.org/licenses/>.
*/
#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* Compilation: gcc -o spkmodem-recv spkmodem-recv.c */
/* Usage: parec --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv */
#define SAMPLES_PER_FRAME 240
#define MAX_SAMPLES (2 * SAMPLES_PER_FRAME)
#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 ERR() (errno = errno ? errno : ECANCELED)
#define reset_char() ascii = 0, ascii_bit = 7
signed short frame[MAX_SAMPLES], pulse[MAX_SAMPLES];
int ringpos, debug, freq_data, freq_separator, sample_count, ascii_bit = 7;
char ascii = 0;
void handle_audio(void);
void fetch_sample(void);
void read_frame(void);
int set_ascii_bit(void);
void print_char(void);
void print_stats(void);
int
main(int argc, char *argv[])
{
int c;
#ifdef __OpenBSD__
if (pledge("stdio", NULL) == -1)
err(ERR(), "pledge");
#endif
while ((c = getopt(argc, argv, "d")) != -1)
if (!(debug = (c == 'd')))
err(errno = EINVAL, NULL);
setvbuf(stdout, NULL, _IONBF, 0);
while (!feof(stdin))
handle_audio();
if (errno && debug)
err(errno, "Unhandled error, errno %d", errno);
return errno;
}
void
handle_audio(void)
{
if (sample_count > (3 * SAMPLES_PER_FRAME))
sample_count = reset_char();
if ((freq_separator <= FREQ_SEP_MIN) || (freq_separator >= FREQ_SEP_MAX)
|| (freq_data <= FREQ_DATA_MIN) || (freq_data >= FREQ_DATA_MAX)) {
fetch_sample();
return;
}
if (set_ascii_bit() < 0)
print_char();
sample_count = 0;
for (int sample = 0; sample < SAMPLES_PER_FRAME; sample++)
fetch_sample();
}
void
fetch_sample(void)
{
int next_ringpos = (ringpos + SAMPLES_PER_FRAME) % MAX_SAMPLES;
freq_data -= pulse[ringpos];
freq_data += pulse[next_ringpos];
freq_separator -= pulse[next_ringpos];
read_frame();
if ((pulse[ringpos] = (abs(frame[ringpos]) > THRESHOLD) ? 1 : 0))
++freq_separator;
++ringpos;
ringpos %= MAX_SAMPLES;
++sample_count;
}
void
read_frame(void)
{
if ((fread(frame + ringpos, 1, sizeof(frame[0]), stdin)
!= sizeof(frame[0])) || (ferror(stdin) != 0))
err(ERR(), "Could not read from frame.");
}
int
set_ascii_bit(void)
{
if (debug)
print_stats();
if (freq_data < FREQ_DATA_THRESHOLD)
ascii |= (1 << ascii_bit);
--ascii_bit;
return ascii_bit;
}
void
print_char(void)
{
if (debug)
printf("<%c, %x>", ascii, ascii);
else
printf("%c", ascii);
reset_char();
}
void
print_stats(void)
{
long stdin_pos;
if ((stdin_pos = ftell(stdin)) == -1)
err(ERR(), NULL);
printf ("%d %d %d @%ld\n", freq_data, freq_separator,
FREQ_DATA_THRESHOLD, stdin_pos - sizeof(frame));
}
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