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| -rw-r--r-- | README | 2 | ||||
| -rw-r--r-- | src/send.c | 138 |
2 files changed, 139 insertions, 1 deletions
@@ -1,2 +1,2 @@ -File over fual-tone multi-frequency signaling +File over dual-tone multi-frequency signaling diff --git a/src/send.c b/src/send.c new file mode 100644 index 0000000..d457bbb --- /dev/null +++ b/src/send.c @@ -0,0 +1,138 @@ +/** + * Copyright © 2015 Mattias Andrée (maandree@member.fsf.org) + * + * This program 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 3 of the License, or + * (at your option) any later version. + * + * This program 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 this program. If not, see <http://www.gnu.org/licenses/>. + */ +#include <stdio.h> +#include <math.h> /* -lm */ +#include <stdint.h> +#include <alsa/asoundlib.h> /* dep: alsa-lib (pkg-config alsa) */ + + +#define UTYPE uint32_t +#define SMIN INT32_MIN +#define SMAX INT32_MAX +#define FORMAT SND_PCM_FORMAT_U32 + +#define SAMPLE_RATE 52000 /* Hz */ +#define DURATION 100 /* ms */ /* 100 ms → 10 Bd → 5 B/s */ +#define LATENCY 100000 /* µs */ + + +#define N(buf) (sizeof(buf) / sizeof(*buf)) + + +static const char* argv0; +static snd_pcm_t* sound_handle = NULL; + + +void get_freq(int nibble, int* low, int* high) +{ + static const int LOW[] = { 697, 770, 852, 941 }; + static const int HIGH[] = { 1209, 1336, 1477, 1663 }; + + *low = LOW[(nibble >> 0) & 0x03]; + *high = HIGH[(nibble >> 2) & 0x03]; +} + +int send_tones(int low, int high) +{ +#define GENERATE_TONE(tone) \ + sin(2 * M_PI * ((double)i / (SAMPLE_RATE / tone))) + + static UTYPE buffer[SAMPLE_RATE / 1000 * DURATION]; + snd_pcm_sframes_t frames; + int r; + size_t i; + + for (i = 0; i < N(buffer); i++) + buffer[i] = (GENERATE_TONE(low) + GENERATE_TONE(high)) * (SMAX / 2) - SMIN; + + r = frames = snd_pcm_writei(sound_handle, buffer, N(buffer)); + if (frames < 0) + r = frames = snd_pcm_recover(sound_handle, r, 0 /* do not print error reason? */); + if (r < 0) + { + fprintf(stderr, "%s: snd_pcm_writei: %s\n", argv0, snd_strerror(r)); + return -1; + } + if ((r > 0) && ((size_t)r < N(buffer))) + printf("%s: short write: expected %zu, wrote %zu\n", argv0, N(buffer), (size_t)frames); + + return 0; +} + +int send_byte(int c) +{ + int low1, high1, low2, high2; + get_freq((c >> 0) & 0x0F, &low1, &high1); + get_freq((c >> 4) & 0x0F, &low2, &high2); + if (send_tones(low1, high1)) + return -1; + if (send_tones(low2, high2)) + return -1; + return 0; +} + + +int main(int argc, char* argv[]) +{ + int r; + char buf[1024]; + ssize_t n, i; + + (void) argc; + argv0 = argv[0]; + + r = snd_pcm_open(&sound_handle, "default", SND_PCM_STREAM_PLAYBACK, 0); + if (r < 0) + return + fprintf(stderr, "%s: snd_pcm_open: %s\n", *argv, snd_strerror(r)), + 1; + + r = snd_pcm_set_params(sound_handle, + FORMAT, + SND_PCM_ACCESS_RW_INTERLEAVED, + 1, /* channels */ + SAMPLE_RATE, + 1, /* allow resampling? */ + LATENCY); + if (r < 0) + { + fprintf(stderr, "%s: snd_pcm_set_params: %s\n", *argv, snd_strerror(r)); + goto snd_fail; + } + + for (;;) + { + n = read(STDIN_FILENO, buf, sizeof(buf)); + if (n < 0) + goto fail; + if (n == 0) + break; + for (i = 0; i < n; i++) + if (send_byte(buf[i])) + goto snd_fail; + } + + snd_pcm_close(sound_handle); + return 0; + fail: + perror(argv0); + return 1; + snd_fail: + snd_pcm_close(sound_handle); + return 1; +} + |