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-rw-r--r--src/send.c51
1 files changed, 33 insertions, 18 deletions
diff --git a/src/send.c b/src/send.c
index 2094fee..54b0c1d 100644
--- a/src/send.c
+++ b/src/send.c
@@ -17,13 +17,14 @@
#include "common.h"
#include <stdio.h>
-#include <math.h> /* -lm */
#include <stdint.h>
-#include <alsa/asoundlib.h> /* dep: alsa-lib (pkg-config alsa) */
#include <signal.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
+#include <string.h>
+#include <math.h> /* -lm */
+#include <alsa/asoundlib.h> /* dep: alsa-lib (pkg-config alsa) */
@@ -36,6 +37,9 @@
#define DURATION 100 /* ms */ /* 100 ms → 10 Bd → 5 B/s */
#define LATENCY 100000 /* µs */
+#define PARITY 2
+#define USE_EXTRA_PARITY 0
+
/**
@@ -150,6 +154,7 @@ static int send_nibble(int n)
*/
static int send_byte(int c)
{
+ printf("%i\n", c);
if (send_nibble((c >> 0) & 0x0F)) return -1;
if (send_nibble((c >> 4) & 0x0F)) return -1;
return 0;
@@ -173,38 +178,45 @@ static int send_byte(int c)
*/
static int send_byte_with_ecc(int c)
{
- static int data[4];
+ static int data[(1 << PARITY) - PARITY - 1];
static int ptr = 0;
- int code[8];
- int i, rc = 1;
+ static int code[(1 << PARITY) - 1 + USE_EXTRA_PARITY];
+ int i, j, d, p;
/* Fill buffer. */
if (c < 0)
{
if (ptr > 0)
- while (ptr < 4)
+ while (ptr < sizeof(data) / sizeof(*data))
data[ptr++] = -c;
}
else
data[ptr++] = c;
/* Is it full? */
- if (ptr < 4)
+ if (ptr < sizeof(data) / sizeof(*data))
return 0;
ptr = 0;
/* Hamming code. */
- code[0] = data[0] ^ data[1] ^ data[3];
- code[1] = data[0] ^ data[2] ^ data[3];
- code[2] = data[0];
- code[3] = data[1] ^ data[2] ^ data[3];
- code[4] = data[1];
- code[5] = data[2];
- code[6] = data[3];
- code[7] = data[0] ^ data[1] ^ data[2] ^ data[3];
+ memset(code, 0, sizeof(code));
+ for (i = 1, j = 0; i <= (1 << PARITY) - 1; i++)
+ {
+ if ((i & -i) == i)
+ continue;
+ for (d = i, p = 0; d; d >>= 1, p++)
+ if (d & 1)
+ code[(1 << p) - 1] ^= data[j];
+ code[i - 1] = data[j];
+ j++;
+ }
+#ifdef USE_EXTRA_PARITY
+ for (i = 0; i < sizeof(data) / sizeof(*data); i++)
+ code[(1 << PARITY) - 1] ^= data[i];
+#endif
/* Transmit. */
- for (i = 0; i < 8; i++)
+ for (i = 0; i < sizeof(code) / sizeof(*code); i++)
if (send_byte(code[i]))
return -1;
@@ -371,8 +383,11 @@ int main(int argc, char* argv[])
cleanup:
snd_pcm_close(sound_handle);
/* Mark aborted transmission. */
- send_byte_with_ecc(CHAR_CANCEL);
- send_byte_with_ecc(-CHAR_CANCEL);
+ if (rc)
+ {
+ send_byte_with_ecc(CHAR_CANCEL);
+ send_byte_with_ecc(-CHAR_CANCEL);
+ }
return rc;
}