136 lines
2.5 KiB
C
136 lines
2.5 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 DEBUG 0
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#define FLUSH_TIMEOUT 1
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signed short frame[2 * SAMPLES_PER_FRAME];
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signed short pulse[2 * SAMPLES_PER_FRAME];
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int f1, f2, lp, ascii_bit = 7;
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char ascii = 0;
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void handle_audio(void);
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void print_char(void);
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void fetch_sample(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(errno, "pledge");
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#endif
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while ((c = getopt(argc, argv, "u")) != -1) {
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switch (c) {
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case 'u':
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setvbuf(stdout, NULL, _IONBF, 0);
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break;
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default:
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err(errno = EINVAL, NULL);
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}
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}
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while (!feof(stdin))
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handle_audio();
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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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static int llp = 0;
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if (lp > (3 * SAMPLES_PER_FRAME)) {
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ascii_bit = 7;
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ascii = 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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if (fflush(stdout) == EOF)
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err(errno, NULL);
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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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fetch_sample();
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return;
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}
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print_char();
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lp = 0;
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llp = 0;
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for (int i = 0; i < SAMPLES_PER_FRAME; i++)
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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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static int ringpos = 0;
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f1 -= pulse[ringpos];
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f1 += pulse[(ringpos + SAMPLES_PER_FRAME) % (2 * SAMPLES_PER_FRAME)];
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f2 -= pulse[(ringpos + SAMPLES_PER_FRAME) % (2 * SAMPLES_PER_FRAME)];
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if (fread(frame + ringpos, 1, sizeof(frame[0]), stdin)
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!= sizeof(frame[0]))
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err(errno = ECANCELED, "Could not read frame.");
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if (abs(frame[ringpos]) > THRESHOLD) { /* rising/falling edge(pulse) */
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pulse[ringpos] = 1;
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f2++;
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} else {
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pulse[ringpos] = 0;
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}
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ringpos++;
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ringpos %= 2 * SAMPLES_PER_FRAME;
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lp++;
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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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long stdin_pos = 0;
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if ((stdin_pos = ftell(stdin)) == -1)
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err(errno, NULL);
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printf ("%d %d %d @%ld\n", f1, f2, FREQ_DATA_THRESHOLD,
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stdin_pos - sizeof(frame));
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#endif
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if (f1 < FREQ_DATA_THRESHOLD)
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ascii |= (1 << ascii_bit);
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ascii_bit--;
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if (ascii_bit < 0) {
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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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#endif
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ascii_bit = 7;
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ascii = 0;
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}
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}
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