130 lines
2.8 KiB
C
130 lines
2.8 KiB
C
/* spkmodem-recv.c - decode spkmodem signals */
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/* SPDX-License-Identifier: GPL-2.0-or-later */
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#include <err.h>
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#include <errno.h>
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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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#include <unistd.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_FRAME 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 ERR() (errno = errno ? errno : ECANCELED)
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#define reset_char() ascii = 0, ascii_bit = 7
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signed short frame[2 * SAMPLES_PER_FRAME], pulse[2 * SAMPLES_PER_FRAME];
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int ringpos, debug, freq_data, freq_separator, sample_count, ascii_bit = 7;
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char ascii = 0;
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void handle_audio(void);
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void fetch_sample(void);
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void read_frame(void);
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int set_ascii_bit(void);
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void print_char(void);
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void print_stats(void);
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int
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main(int argc, char *argv[])
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{
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int c;
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#ifdef __OpenBSD__
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if (pledge("stdio", NULL) == -1)
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err(ERR(), "pledge");
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#endif
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while ((c = getopt(argc, argv, "d")) != -1) {
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if (c != 'd')
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err(errno = EINVAL, NULL);
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debug = 1;
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}
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setvbuf(stdout, NULL, _IONBF, 0);
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while (!feof(stdin))
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handle_audio();
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if (errno && debug)
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err(errno, "Unhandled error, errno %d", errno);
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return errno;
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}
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void
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handle_audio(void)
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{
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if (sample_count > (3 * SAMPLES_PER_FRAME))
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sample_count = reset_char();
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if ((freq_separator <= FREQ_SEP_MIN) || (freq_separator >= FREQ_SEP_MAX)
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|| (freq_data <= FREQ_DATA_MIN) || (freq_data >= FREQ_DATA_MAX)) {
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fetch_sample();
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return;
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}
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if (set_ascii_bit() < 0)
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print_char();
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sample_count = 0;
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for (int sample = 0; sample < SAMPLES_PER_FRAME; sample++)
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fetch_sample();
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}
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void
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fetch_sample(void)
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{
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freq_data -= pulse[ringpos];
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freq_data += pulse[(ringpos + SAMPLES_PER_FRAME)
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% (2 * SAMPLES_PER_FRAME)];
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freq_separator -= pulse[(ringpos + SAMPLES_PER_FRAME)
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% (2 * SAMPLES_PER_FRAME)];
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read_frame();
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if ((pulse[ringpos] = (abs(frame[ringpos]) > THRESHOLD) ? 1 : 0))
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++freq_separator;
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++ringpos;
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ringpos %= 2 * SAMPLES_PER_FRAME;
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++sample_count;
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}
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void
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read_frame(void)
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{
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if ((fread(frame + ringpos, 1, sizeof(frame[0]), stdin)
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!= sizeof(frame[0])) || (ferror(stdin) != 0))
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err(ERR(), "Could not read from frame.");
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}
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int
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set_ascii_bit(void)
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{
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if (debug)
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print_stats();
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if (freq_data < FREQ_DATA_THRESHOLD)
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ascii |= (1 << ascii_bit);
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--ascii_bit;
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return ascii_bit;
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}
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void
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print_char(void)
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{
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if (debug)
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printf("<%c, %x>", ascii, ascii);
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else
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printf("%c", ascii);
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reset_char();
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}
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void
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print_stats(void)
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{
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long stdin_pos = 0;
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if ((stdin_pos = ftell(stdin)) == -1)
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err(ERR(), NULL);
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printf ("%d %d %d @%ld\n", freq_data, freq_separator,
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FREQ_DATA_THRESHOLD, stdin_pos - sizeof(frame));
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}
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