diff options
| -rw-r--r-- | src/send.c | 51 |
1 files changed, 33 insertions, 18 deletions
@@ -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; } |