From 29b6cacc6ffece36f48bb8634b590cd82d96bf8b Mon Sep 17 00:00:00 2001 From: marshmellow42 Date: Sun, 5 Jul 2015 23:35:00 -0400 Subject: [PATCH] more verification on FDX-B tag demod - reduce... ... false positives --- client/cmddata.c | 4 ++-- common/lfdemod.c | 10 ++++++---- 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/client/cmddata.c b/client/cmddata.c index bec1b5aa..bf10a6ec 100644 --- a/client/cmddata.c +++ b/client/cmddata.c @@ -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; } diff --git a/common/lfdemod.c b/common/lfdemod.c index f13a567c..a3a7a500 100644 --- a/common/lfdemod.c +++ b/common/lfdemod.c @@ -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; -- 2.39.2