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Add fuzzy syncword validation 

Now syncword match is not exact but can tolerate up to two erroneous
bits.

TG-81
This commit is contained in:
Niccolò Izzo 2022-02-08 14:44:05 +01:00 committed by Silvano Seva
parent ca49b306b9
commit 5ef145cd39
2 changed files with 16 additions and 5 deletions
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5
openrtx/include/protocols/M17/M17Demodulator.h
View File

@ -252,6 +252,11 @@ private:
*/ */
int8_t quantize(int32_t offset); int8_t quantize(int32_t offset);
/**
* Compute Hamming Distance between two bytes
*/
uint8_t hammingDistance(uint8_t x, uint8_t y);
}; };
} /* M17 */ } /* M17 */

16
openrtx/src/protocols/M17/M17Demodulator.cpp
View File

@ -272,6 +272,11 @@ bool M17Demodulator::isFrameLSF()
return isLSF; return isLSF;
} }
uint8_t M17Demodulator::hammingDistance(uint8_t x, uint8_t y)
{
return __builtin_popcount(x ^ y);
}
void M17Demodulator::update() void M17Demodulator::update()
{ {
M17::sync_t syncword = { 0, false }; M17::sync_t syncword = { 0, false };
@ -283,6 +288,7 @@ void M17Demodulator::update()
FILE *csv_log = fopen("demod_log_2.csv", "a"); FILE *csv_log = fopen("demod_log_2.csv", "a");
#endif #endif
if(baseband.data != NULL) if(baseband.data != NULL)
{ {
// Apply RRC on the baseband buffer // Apply RRC on the baseband buffer
@ -342,12 +348,12 @@ void M17Demodulator::update()
// printf(" %02X%02X", (*idleFrame)[i], (*idleFrame)[i+1]); // printf(" %02X%02X", (*idleFrame)[i], (*idleFrame)[i+1]);
//} //}
} }
// Check if the decoded syncword matches with frame or lsf sync // If syncword is not valid, lock is lost, accept 2 bit errors
if (frameIndex == M17_SYNCWORD_SYMBOLS && if (frameIndex == M17_SYNCWORD_SYMBOLS &&
((*activeFrame)[0] != stream_syncword_bytes[0] || (hammingDistance((*activeFrame)[0], stream_syncword_bytes[0]) +
(*activeFrame)[1] != stream_syncword_bytes[1]) && hammingDistance((*activeFrame)[1], stream_syncword_bytes[1]) > 2) &&
((*activeFrame)[0] != lsf_syncword_bytes[0] || (hammingDistance((*activeFrame)[0], lsf_syncword_bytes[0]) +
(*activeFrame)[1] != lsf_syncword_bytes[1])) hammingDistance((*activeFrame)[1], lsf_syncword_bytes[1]) > 2))
{ {
locked = false; locked = false;
std::swap(activeFrame, idleFrame); std::swap(activeFrame, idleFrame);