draft

Signed-off-by: Mattias Andrée <maandree@member.fsf.org>

2 files changed, 139 insertions, 1 deletions

diff --git a/README b/README
index 51bc22b..f5138cc 100644
--- a/README
+++ b/README
@@ -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;
+}
+