NMT: Changes in parity check

pull/1/head
Andreas Eversberg 7 years ago
parent 28e7f1e9d1
commit 47dbf094d9
  1. 49
      src/nmt/frame.c

@ -879,6 +879,9 @@ static void encode_digits(const uint8_t *digits, char *bits)
bits[(i << 1) + 1] = x[i - 6] + '0';
}
/* debug parity check */
//#define DEBUG_DECODE
/* decode digits from 140 bits (not including sync) */
// FIXME: do real convolutional decoding
static int decode_digits(uint8_t *digits, const char *bits, int callack)
@ -888,8 +891,12 @@ static int decode_digits(uint8_t *digits, const char *bits, int callack)
/* information bits */
for (i = 0; i < 6; i++) {
if (bits[(i << 1) + 1] != '0')
if (bits[(i << 1) + 1] != '0') {
#ifdef DEBUG_DECODE
PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at information bit #%d.\n", i);
#endif
return -1;
}
}
for (i = 6; i < 70; i++)
x[i - 6] = bits[(i << 1) + 1] - '0';
@ -908,13 +915,22 @@ static int decode_digits(uint8_t *digits, const char *bits, int callack)
digits[14] = 0;
digits[15] = 0;
short_frame = 1;
#ifdef DEBUG_DECODE
PDEBUG(DFRAME, DEBUG_DEBUG, "Received shortened frame\n");
#endif
}
/* parity check bits */
for (i = 0; i < 3; i++) {
if (bits[(i << 1)] != '1' - x[i])
if (bits[(i << 1)] != '1' - x[i]) {
#ifdef DEBUG_DECODE
PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
#endif
return -1;
}
}
#if 0
#warning this check does not work, since we get error even at bit 50
for (i = 3; i < ((short_frame) ? 52 : 64); i++) {
if (bits[(i << 1)] != '1' - (x[i] ^ x[i - 3])) {
/* According to NMT Doc 450-3, bits after Y(114) shall
@ -930,18 +946,43 @@ static int decode_digits(uint8_t *digits, const char *bits, int callack)
digits[13] = 0;
break;
}
#ifdef DEBUG_DECODE
PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
#endif
return -1;
}
}
#endif
/* Tests showed corrupt frame at parity #50 (i == 50)
* We just ignore whatever we receive after 48 bits of checksum.
* This is not the correct approach, but in case of a corrupt
* frame 10.a, we would drop it, if it failes later checks.
*/
for (i = 3; i < ((short_frame) ? 48 : 64); i++) {
if (bits[(i << 1)] != '1' - (x[i] ^ x[i - 3])) {
#ifdef DEBUG_DECODE
PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
#endif
return -1;
}
}
if (short_frame)
return 0;
for (i = 64; i < 67; i++) {
if (bits[(i << 1)] != '1' - x[i - 3])
if (bits[(i << 1)] != '1' - x[i - 3]) {
#ifdef DEBUG_DECODE
PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
#endif
return -1;
}
}
for (i = 67; i < 70; i++) {
if (bits[(i << 1)] != '1')
if (bits[(i << 1)] != '1') {
#ifdef DEBUG_DECODE
PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
#endif
return -1;
}
}
return 0;

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