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more verification on FDX-B tag demod - reduce...

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... false positives
This commit is contained in:
marshmellow42 2015-07-05 23:35:00 -04:00
parent 7ce6e2c0b5
commit 29b6cacc6f
2 changed files with 8 additions and 6 deletions
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4
client/cmddata.c
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@ -1491,9 +1491,9 @@ int CmdFDXBdemodBI(const char *Cmd){
setDemodBuf(BitStream, 128, preambleIndex);
// remove but don't verify parity. (pType = 2)
// remove marker bits (1's every 9th digit after preamble) (pType = 2)
size = removeParity(BitStream, preambleIndex + 11, 9, 2, 117);
if ( size <= 103 ) {
if ( size != 104 ) {
if (g_debugMode) PrintAndLog("Error removeParity:: %d", size);
return 0;
}

10
common/lfdemod.c
View file

@ -580,7 +580,7 @@ int IOdemodFSK(uint8_t *dest, size_t size)
// by marshmellow
// takes a array of binary values, start position, length of bits per parity (includes parity bit),
// Parity Type (1 for odd; 0 for even; 2 for just drop it), and binary Length (length to run)
// Parity Type (1 for odd; 0 for even; 2 Always 1's), and binary Length (length to run)
size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t pType, size_t bLen)
{
uint32_t parityWd = 0;
@ -590,10 +590,12 @@ size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t p
parityWd = (parityWd << 1) | BitStream[startIdx+word+bit];
BitStream[j++] = (BitStream[startIdx+word+bit]);
}
j--;
j--; // overwrite parity with next data
// if parity fails then return 0
if (pType != 2) {
if (parityTest(parityWd, pLen, pType) == 0) return -1;
if (pType == 2) { // then marker bit which should be a 1
if (!BitStream[j]) return 0;
} else {
if (parityTest(parityWd, pLen, pType) == 0) return 0;
}
bitCnt+=(pLen-1);
parityWd = 0;