/**
* 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 * 1) + GENERATE_TONE(high * 1) +
GENERATE_TONE(low * 4) + GENERATE_TONE(high * 4)) *
(SMAX / 4) - 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;
}
