small text adjustments plus...

[proxmark3-svn] / common / lfdemod.c

diff --git a/common/lfdemod.c b/common/lfdemod.c
index cf11b25b8d1ea28fef82c7622ba526f54e78b99c..e9f19311c8b6c248d0ffcdabd1b4e1bc3c04f1c9 100644 (file)
--- a/common/lfdemod.c
+++ b/common/lfdemod.c
@@ -62,7 +62,7 @@ uint8_t parityTest(uint32_t bits, uint8_t bitLen, uint8_t pType)
        for (uint8_t i = 0; i < bitLen; i++){
                ans ^= ((bits >> i) & 1);
        }
        for (uint8_t i = 0; i < bitLen; i++){
                ans ^= ((bits >> i) & 1);
        }

-       //PrintAndLog("DEBUG: ans: %d, ptype: %d",ans,pType);
+       if (g_debugMode) prnt("DEBUG: ans: %d, ptype: %d, bits: %08X",ans,pType,bits);

        return (ans == pType);
 }
 
        return (ans == pType);
 }
 


@@ -73,18 +73,19 @@ size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t p
 {
        uint32_t parityWd = 0;
        size_t j = 0, bitCnt = 0;
 {
        uint32_t parityWd = 0;
        size_t j = 0, bitCnt = 0;

-       for (int word = 0; word < (bLen); word+=pLen){
-               for (int bit=0; bit < pLen; bit++){
+       for (int word = 0; word < (bLen); word+=pLen) {
+               for (int bit=0; bit < pLen; bit++) {

                        parityWd = (parityWd << 1) | BitStream[startIdx+word+bit];
                        BitStream[j++] = (BitStream[startIdx+word+bit]);
                }
                        parityWd = (parityWd << 1) | BitStream[startIdx+word+bit];
                        BitStream[j++] = (BitStream[startIdx+word+bit]);
                }

+               if (word+pLen >= bLen) break;
+

                j--; // overwrite parity with next data
                // if parity fails then return 0
                switch (pType) {
                j--; // overwrite parity with next data
                // if parity fails then return 0
                switch (pType) {

-                       case 3: if (BitStream[j]==1) return 0; break; //should be 0 spacer bit
-                       case 2: if (BitStream[j]==0) return 0; break; //should be 1 spacer bit
-                       default: //test parity
-                               if (parityTest(parityWd, pLen, pType) == 0) return 0; break;
+                       case 3: if (BitStream[j]==1) {return 0;} break; //should be 0 spacer bit
+                       case 2: if (BitStream[j]==0) {return 0;} break; //should be 1 spacer bit
+                       default: if (parityTest(parityWd, pLen, pType) == 0) {return 0;} break; //test parity

                }
                bitCnt+=(pLen-1);
                parityWd = 0;
                }
                bitCnt+=(pLen-1);
                parityWd = 0;


@@ -149,6 +150,9 @@ uint32_t bytebits_to_byteLSBF(uint8_t *src, size_t numbits)
 //search for given preamble in given BitStream and return success=1 or fail=0 and startIndex and length
 uint8_t preambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_t *size, size_t *startIdx)
 {
 //search for given preamble in given BitStream and return success=1 or fail=0 and startIndex and length
 uint8_t preambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_t *size, size_t *startIdx)
 {

+       // Sanity check.  If preamble length is bigger than bitstream length.
+       if ( *size <= pLen ) return 0;
+

        uint8_t foundCnt=0;
        for (int idx=0; idx < *size - pLen; idx++){
                if (memcmp(BitStream+idx, preamble, pLen) == 0){
        uint8_t foundCnt=0;
        for (int idx=0; idx < *size - pLen; idx++){
                if (memcmp(BitStream+idx, preamble, pLen) == 0){


@@ -166,6 +170,49 @@ uint8_t preambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_
        return 0;
 }
 
        return 0;
 }
 

+// search for given preamble in given BitStream and return success=1 or fail=0 and startIndex (where it was found)
+// does not look for a repeating preamble
+// em4x05/4x69 only sends preamble once, so look for it once in the first pLen bits
+// leave it generic so it could be reused later...
+bool onePreambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_t size, size_t *startIdx) {
+       // Sanity check.  If preamble length is bigger than bitstream length.
+       if ( size <= pLen ) return false;
+       for (size_t idx = 0; idx < size - pLen; idx++) {
+               if (memcmp(BitStream+idx, preamble, pLen) == 0) {
+                       if (g_debugMode) prnt("DEBUG: preamble found at %u", idx);
+                       *startIdx = idx;
+                       return true;
+               }
+       }
+       return false;
+}
+
+// find start of modulating data (for fsk and psk) in case of beginning noise or slow chip startup.
+size_t findModStart(uint8_t dest[], size_t size, uint8_t threshold_value, uint8_t expWaveSize) {
+       size_t i = 0;
+       size_t waveSizeCnt = 0;
+       uint8_t thresholdCnt = 0;
+       bool isAboveThreshold = dest[i++] >= threshold_value;
+       for (; i < size-20; i++ ) {
+               if(dest[i] < threshold_value && isAboveThreshold) {
+                       thresholdCnt++;
+                       if (thresholdCnt > 2 && waveSizeCnt < expWaveSize+1) break;                     
+                       isAboveThreshold = false;
+                       waveSizeCnt = 0;
+               } else if (dest[i] >= threshold_value && !isAboveThreshold) {
+                       thresholdCnt++;
+                       if (thresholdCnt > 2 && waveSizeCnt < expWaveSize+1) break;                     
+                       isAboveThreshold = true;
+                       waveSizeCnt = 0;
+               } else {
+                       waveSizeCnt++;
+               }
+               if (thresholdCnt > 10) break;
+       }
+       if (g_debugMode == 2) prnt("DEBUG: threshold Count reached at %u, count: %u",i, thresholdCnt);
+       return i;
+}
+

 //by marshmellow
 //takes 1s and 0s and searches for EM410x format - output EM ID
 uint8_t Em410xDecode(uint8_t *BitStream, size_t *size, size_t *startIdx, uint32_t *hi, uint64_t *lo)
 //by marshmellow
 //takes 1s and 0s and searches for EM410x format - output EM ID
 uint8_t Em410xDecode(uint8_t *BitStream, size_t *size, size_t *startIdx, uint32_t *hi, uint64_t *lo)


@@ -260,15 +307,18 @@ int cleanAskRawDemod(uint8_t *BinStream, size_t *size, int clk, int invert, int
 //by marshmellow
 void askAmp(uint8_t *BitStream, size_t size)
 {
 //by marshmellow
 void askAmp(uint8_t *BitStream, size_t size)
 {

+       uint8_t Last = 128;

        for(size_t i = 1; i<size; i++){
                if (BitStream[i]-BitStream[i-1]>=30) //large jump up
        for(size_t i = 1; i<size; i++){
                if (BitStream[i]-BitStream[i-1]>=30) //large jump up

-                       BitStream[i]=255;
-               else if(BitStream[i]-BitStream[i-1]<=-20) //large jump down
-                       BitStream[i]=0;
+                       Last = 255;
+               else if(BitStream[i-1]-BitStream[i]>=20) //large jump down
+                       Last = 0;
+
+               BitStream[i-1] = Last;

        }
        return;
 }
        }
        return;
 }

-
+ 

 //by marshmellow
 //attempts to demodulate ask modulations, askType == 0 for ask/raw, askType==1 for ask/manchester
 int askdemod(uint8_t *BinStream, size_t *size, int *clk, int *invert, int maxErr, uint8_t amp, uint8_t askType)
 //by marshmellow
 //attempts to demodulate ask modulations, askType == 0 for ask/raw, askType==1 for ask/manchester
 int askdemod(uint8_t *BinStream, size_t *size, int *clk, int *invert, int maxErr, uint8_t amp, uint8_t askType)


@@ -278,7 +328,7 @@ int askdemod(uint8_t *BinStream, size_t *size, int *clk, int *invert, int maxErr
        if (*clk==0 || start < 0) return -3;
        if (*invert != 1) *invert = 0;
        if (amp==1) askAmp(BinStream, *size);
        if (*clk==0 || start < 0) return -3;
        if (*invert != 1) *invert = 0;
        if (amp==1) askAmp(BinStream, *size);

-       if (g_debugMode==2) prnt("DEBUG ASK: clk %d, beststart %d", *clk, start);
+       if (g_debugMode==2) prnt("DEBUG ASK: clk %d, beststart %d, amp %d", *clk, start, amp);

 
        uint8_t initLoopMax = 255;
        if (initLoopMax > *size) initLoopMax = *size;
 
        uint8_t initLoopMax = 255;
        if (initLoopMax > *size) initLoopMax = *size;


@@ -472,7 +522,6 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
 {
        size_t last_transition = 0;
        size_t idx = 1;
 {
        size_t last_transition = 0;
        size_t idx = 1;

-       //uint32_t maxVal=0;

        if (fchigh==0) fchigh=10;
        if (fclow==0) fclow=8;
        //set the threshold close to 0 (graph) or 128 std to avoid static
        if (fchigh==0) fchigh=10;
        if (fclow==0) fclow=8;
        //set the threshold close to 0 (graph) or 128 std to avoid static


@@ -480,19 +529,22 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
        size_t preLastSample = 0;
        size_t LastSample = 0;
        size_t currSample = 0;
        size_t preLastSample = 0;
        size_t LastSample = 0;
        size_t currSample = 0;

-       // sync to first lo-hi transition, and threshold
+       if ( size < 1024 ) return 0; // not enough samples
+
+       //find start of modulating data in trace 
+       idx = findModStart(dest, size, threshold_value, fchigh);

 
        // Need to threshold first sample
 
        // Need to threshold first sample

-       // skip 160 samples to allow antenna/samples to settle
-       if(dest[160] < threshold_value) dest[0] = 0;
+       if(dest[idx] < threshold_value) dest[0] = 0;

        else dest[0] = 1;
        else dest[0] = 1;

-
+       idx++;
+       

        size_t numBits = 0;
        // count cycles between consecutive lo-hi transitions, there should be either 8 (fc/8)
        // or 10 (fc/10) cycles but in practice due to noise etc we may end up with anywhere
        // between 7 to 11 cycles so fuzz it by treat anything <9 as 8 and anything else as 10
        //  (could also be fc/5 && fc/7 for fsk1 = 4-9)
        size_t numBits = 0;
        // count cycles between consecutive lo-hi transitions, there should be either 8 (fc/8)
        // or 10 (fc/10) cycles but in practice due to noise etc we may end up with anywhere
        // between 7 to 11 cycles so fuzz it by treat anything <9 as 8 and anything else as 10
        //  (could also be fc/5 && fc/7 for fsk1 = 4-9)

-       for(idx = 161; idx < size-20; idx++) {
+       for(; idx < size-20; idx++) {

                // threshold current value
 
                if (dest[idx] < threshold_value) dest[idx] = 0;
                // threshold current value
 
                if (dest[idx] < threshold_value) dest[idx] = 0;


@@ -507,13 +559,14 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
                                //do nothing with extra garbage
                        } else if (currSample < (fchigh-1)) {           //6-8 = 8 sample waves  (or 3-6 = 5)
                                //correct previous 9 wave surrounded by 8 waves (or 6 surrounded by 5)
                                //do nothing with extra garbage
                        } else if (currSample < (fchigh-1)) {           //6-8 = 8 sample waves  (or 3-6 = 5)
                                //correct previous 9 wave surrounded by 8 waves (or 6 surrounded by 5)

-                               if (LastSample > (fchigh-2) && (preLastSample < (fchigh-1) || preLastSample     == 0 )){
+                               if (LastSample > (fchigh-2) && (preLastSample < (fchigh-1))){

                                        dest[numBits-1]=1;
                                }
                                dest[numBits++]=1;
 
                                        dest[numBits-1]=1;
                                }
                                dest[numBits++]=1;
 

-                       } else if (currSample > (fchigh) && !numBits) { //12 + and first bit = unusable garbage 
-                               //do nothing with beginning garbage
+                       } else if (currSample > (fchigh+1) && numBits < 3) { //12 + and first two bit = unusable garbage
+                               //do nothing with beginning garbage and reset..  should be rare..
+                               numBits = 0; 

                        } else if (currSample == (fclow+1) && LastSample == (fclow-1)) { // had a 7 then a 9 should be two 8's (or 4 then a 6 should be two 5's)
                                dest[numBits++]=1;
                        } else {                                        //9+ = 10 sample waves (or 6+ = 7)
                        } else if (currSample == (fclow+1) && LastSample == (fclow-1)) { // had a 7 then a 9 should be two 8's (or 4 then a 6 should be two 5's)
                                dest[numBits++]=1;
                        } else {                                        //9+ = 10 sample waves (or 6+ = 7)


@@ -1290,7 +1343,10 @@ uint8_t detectFSKClk(uint8_t *BitStream, size_t size, uint8_t fcHigh, uint8_t fc
                        continue;               
                // else new peak 
                // if we got less than the small fc + tolerance then set it to the small fc
                        continue;               
                // else new peak 
                // if we got less than the small fc + tolerance then set it to the small fc

-               if (fcCounter < fcLow+fcTol) 
+               // if it is inbetween set it to the last counter
+               if (fcCounter < fcHigh && fcCounter > fcLow)
+                       fcCounter = lastFCcnt;
+               else if (fcCounter < fcLow+fcTol) 

                        fcCounter = fcLow;
                else //set it to the large fc
                        fcCounter = fcHigh;
                        fcCounter = fcLow;
                else //set it to the large fc
                        fcCounter = fcHigh;


@@ -1356,7 +1412,7 @@ uint8_t detectFSKClk(uint8_t *BitStream, size_t size, uint8_t fcHigh, uint8_t fc
                }
        }
 
                }
        }
 

-       if (ii<0) return 0; // oops we went too far
+       if (ii<2) return 0; // oops we went too far

 
        return clk[ii];
 }
 
        return clk[ii];
 }


@@ -1370,10 +1426,10 @@ uint16_t countFC(uint8_t *BitStream, size_t size, uint8_t fskAdj)
        uint8_t fcLens[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
        uint16_t fcCnts[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
        uint8_t fcLensFnd = 0;
        uint8_t fcLens[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
        uint16_t fcCnts[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
        uint8_t fcLensFnd = 0;

-       uint8_t lastFCcnt=0;
+       uint8_t lastFCcnt = 0;

        uint8_t fcCounter = 0;
        size_t i;
        uint8_t fcCounter = 0;
        size_t i;

-       if (size == 0) return 0;
+       if (size < 180) return 0;

 
        // prime i to first up transition
        for (i = 160; i < size-20; i++)
 
        // prime i to first up transition
        for (i = 160; i < size-20; i++)


@@ -1460,27 +1516,37 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
 
        size_t numBits=0;
        uint8_t curPhase = *invert;
 
        size_t numBits=0;
        uint8_t curPhase = *invert;

-       size_t i, waveStart=1, waveEnd=0, firstFullWave=0, lastClkBit=0;
-       uint8_t fc=0, fullWaveLen=0, tol=1;
-       uint16_t errCnt=0, waveLenCnt=0;
-       fc = countFC(dest, *size, 0);
+       size_t i=0, waveStart=1, waveEnd=0, firstFullWave=0, lastClkBit=0;
+       uint16_t fc=0, fullWaveLen=0, tol=1;
+       uint16_t errCnt=0, waveLenCnt=0, errCnt2=0;
+       fc = countFC(dest, *size, 1);
+       uint8_t fc2 = fc >> 8;
+       if (fc2 == 10) return -1; //fsk found - quit
+       fc = fc & 0xFF;

        if (fc!=2 && fc!=4 && fc!=8) return -1;
        //PrintAndLog("DEBUG: FC: %d",fc);
        *clock = DetectPSKClock(dest, *size, *clock);
        if (*clock == 0) return -1;
        if (fc!=2 && fc!=4 && fc!=8) return -1;
        //PrintAndLog("DEBUG: FC: %d",fc);
        *clock = DetectPSKClock(dest, *size, *clock);
        if (*clock == 0) return -1;

-       int avgWaveVal=0, lastAvgWaveVal=0;
+
+       //find start of modulating data in trace 
+       uint8_t threshold_value = 123; //-5
+       i = findModStart(dest, *size, threshold_value, fc);
+

        //find first phase shift
        //find first phase shift

-       for (i=0; i<loopCnt; i++){
+       int avgWaveVal=0, lastAvgWaveVal=0;
+       waveStart = i;
+       for (; i<loopCnt; i++) {
+               // find peak 

                if (dest[i]+fc < dest[i+1] && dest[i+1] >= dest[i+2]){
                        waveEnd = i+1;
                if (dest[i]+fc < dest[i+1] && dest[i+1] >= dest[i+2]){
                        waveEnd = i+1;

-                       //PrintAndLog("DEBUG: waveEnd: %d",waveEnd);
+                       if (g_debugMode == 2) prnt("DEBUG PSK: waveEnd: %u, waveStart: %u",waveEnd, waveStart);

                        waveLenCnt = waveEnd-waveStart;
                        waveLenCnt = waveEnd-waveStart;

-                       if (waveLenCnt > fc && waveStart > fc && !(waveLenCnt > fc+2)){ //not first peak and is a large wave but not out of whack
+                       if (waveLenCnt > fc && waveStart > fc && !(waveLenCnt > fc+3)){ //not first peak and is a large wave but not out of whack

                                lastAvgWaveVal = avgWaveVal/(waveLenCnt);
                                firstFullWave = waveStart;
                                fullWaveLen=waveLenCnt;
                                lastAvgWaveVal = avgWaveVal/(waveLenCnt);
                                firstFullWave = waveStart;
                                fullWaveLen=waveLenCnt;

-                               //if average wave value is > graph 0 then it is an up wave or a 1
-                               if (lastAvgWaveVal > 123) curPhase ^= 1;  //fudge graph 0 a little 123 vs 128
+                               //if average wave value is > graph 0 then it is an up wave or a 1 (could cause inverting)
+                               if (lastAvgWaveVal > threshold_value) curPhase ^= 1;

                                break;
                        } 
                        waveStart = i+1;
                                break;
                        } 
                        waveStart = i+1;


@@ -1501,7 +1567,7 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
        //set start of wave as clock align
        lastClkBit = firstFullWave;
        if (g_debugMode==2) prnt("DEBUG PSK: firstFullWave: %u, waveLen: %u",firstFullWave,fullWaveLen);  
        //set start of wave as clock align
        lastClkBit = firstFullWave;
        if (g_debugMode==2) prnt("DEBUG PSK: firstFullWave: %u, waveLen: %u",firstFullWave,fullWaveLen);  

-       if (g_debugMode==2) prnt("DEBUG: clk: %d, lastClkBit: %u, fc: %u", *clock, lastClkBit,(unsigned int) fc);
+       if (g_debugMode==2) prnt("DEBUG PSK: clk: %d, lastClkBit: %u, fc: %u", *clock, lastClkBit,(unsigned int) fc);

        waveStart = 0;
        dest[numBits++] = curPhase; //set first read bit
        for (i = firstFullWave + fullWaveLen - 1; i < *size-3; i++){
        waveStart = 0;
        dest[numBits++] = curPhase; //set first read bit
        for (i = firstFullWave + fullWaveLen - 1; i < *size-3; i++){


@@ -1532,6 +1598,9 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
                                } else if (i+1 > lastClkBit + *clock + tol + fc){
                                        lastClkBit += *clock; //no phase shift but clock bit
                                        dest[numBits++] = curPhase;
                                } else if (i+1 > lastClkBit + *clock + tol + fc){
                                        lastClkBit += *clock; //no phase shift but clock bit
                                        dest[numBits++] = curPhase;

+                               } else if (waveLenCnt < fc - 1) { //wave is smaller than field clock (shouldn't happen often)
+                                       errCnt2++;
+                                       if(errCnt2 > 101) return errCnt2;

                                }
                                avgWaveVal = 0;
                                waveStart = i+1;
                                }
                                avgWaveVal = 0;
                                waveStart = i+1;


@@ -1553,8 +1622,8 @@ bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
        int tol = 0;
        int i, j, skip, start, end, low, high, minClk, waveStart;
        bool complete = false;
        int tol = 0;
        int i, j, skip, start, end, low, high, minClk, waveStart;
        bool complete = false;

-       int tmpbuff[bufsize / 64];
-       int waveLen[bufsize / 64];
+       int tmpbuff[bufsize / 32]; //guess rf/32 clock, if click is smaller we will only have room for a fraction of the samples captured
+       int waveLen[bufsize / 32]; //  if clock is larger then we waste memory in array size that is not needed...

        size_t testsize = (bufsize < 512) ? bufsize : 512;
        int phaseoff = 0;
        high = low = 128;
        size_t testsize = (bufsize < 512) ? bufsize : 512;
        int phaseoff = 0;
        high = low = 128;


@@ -1586,7 +1655,7 @@ bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
                waveStart = i;
                while ((buffer[i] > low) && (i < bufsize))
                        ++i;
                waveStart = i;
                while ((buffer[i] > low) && (i < bufsize))
                        ++i;

-               if (j >= (bufsize/64)) {
+               if (j >= (bufsize/32)) {

                        break;
                }
                waveLen[j] = i - waveStart; //first high to first low
                        break;
                }
                waveLen[j] = i - waveStart; //first high to first low


@@ -1632,6 +1701,8 @@ bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
        if (start < 0) {
                if (g_debugMode==2) prnt("DEBUG STT: first STT not found - quitting");
                return false;
        if (start < 0) {
                if (g_debugMode==2) prnt("DEBUG STT: first STT not found - quitting");
                return false;

+       } else {
+               if (g_debugMode==2) prnt("DEBUG STT: first STT found at: %d, j=%d",start, j);

        }
        if (waveLen[i+2] > clk*1+tol)
                phaseoff = 0;
        }
        if (waveLen[i+2] > clk*1+tol)
                phaseoff = 0;


@@ -1645,7 +1716,7 @@ bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
        end = skip;
        for (i += 3; i < j - 4; ++i) {
                end += tmpbuff[i];
        end = skip;
        for (i += 3; i < j - 4; ++i) {
                end += tmpbuff[i];

-               if (tmpbuff[i] >= clk*1-tol && tmpbuff[i] <= (clk*2)+tol) {           //1 to 2 clocks depending on 2 bits prior
+               if (tmpbuff[i] >= clk*1-tol && tmpbuff[i] <= (clk*2)+tol && waveLen[i] < clk+tol) {           //1 to 2 clocks depending on 2 bits prior

                        if (tmpbuff[i+1] >= clk*2-tol && tmpbuff[i+1] <= clk*2+tol && waveLen[i+1] > clk*3/2-tol) {       //2 clocks and wave size is 1 1/2
                                if (tmpbuff[i+2] >= (clk*3)/2-tol && tmpbuff[i+2] <= clk*2+tol && waveLen[i+2] > clk-tol) { //1 1/2 to 2 clocks and at least one full clock wave
                                        if (tmpbuff[i+3] >= clk*1-tol && tmpbuff[i+3] <= clk*2+tol) { //1 to 2 clocks for end of ST + first bit
                        if (tmpbuff[i+1] >= clk*2-tol && tmpbuff[i+1] <= clk*2+tol && waveLen[i+1] > clk*3/2-tol) {       //2 clocks and wave size is 1 1/2
                                if (tmpbuff[i+2] >= (clk*3)/2-tol && tmpbuff[i+2] <= clk*2+tol && waveLen[i+2] > clk-tol) { //1 1/2 to 2 clocks and at least one full clock wave
                                        if (tmpbuff[i+3] >= clk*1-tol && tmpbuff[i+3] <= clk*2+tol) { //1 to 2 clocks for end of ST + first bit


@@ -1667,12 +1738,15 @@ bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
        start = skip;
        size_t datalen = end - start;
        // check validity of datalen (should be even clock increments)  - use a tolerance of up to 1/8th a clock
        start = skip;
        size_t datalen = end - start;
        // check validity of datalen (should be even clock increments)  - use a tolerance of up to 1/8th a clock

-       if (datalen % clk > clk/8) {
+       if ( clk - (datalen % clk) <= clk/8) {
+               // padd the amount off - could be problematic...  but shouldn't happen often
+               datalen += clk - (datalen % clk);
+       } else if ( (datalen % clk) <= clk/8 ) {
+               // padd the amount off - could be problematic...  but shouldn't happen often
+               datalen -= datalen % clk;
+       } else {

                if (g_debugMode==2) prnt("DEBUG STT: datalen not divisible by clk: %u %% %d = %d - quitting", datalen, clk, datalen % clk);
                return false;
                if (g_debugMode==2) prnt("DEBUG STT: datalen not divisible by clk: %u %% %d = %d - quitting", datalen, clk, datalen % clk);
                return false;

-       } else {
-               // padd the amount off - could be problematic...  but shouldn't happen often
-               datalen += datalen % clk;

        }
        // if datalen is less than one t55xx block - ERROR
        if (datalen/clk < 8*4) {
        }
        // if datalen is less than one t55xx block - ERROR
        if (datalen/clk < 8*4) {


@@ -1680,8 +1754,20 @@ bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
                return false;
        }
        size_t dataloc = start;
                return false;
        }
        size_t dataloc = start;

+       if (buffer[dataloc-(clk*4)-(clk/8)] <= low && buffer[dataloc] <= low && buffer[dataloc-(clk*4)] >= high) {
+               //we have low drift (and a low just before the ST and a low just after the ST) - compensate by backing up the start 
+               for ( i=0; i <= (clk/8); ++i ) {
+                       if ( buffer[dataloc - (clk*4) - i] <= low ) {
+                               dataloc -= i;
+                               break;
+                       }
+               }
+       }
+       

        size_t newloc = 0;
        i=0;
        size_t newloc = 0;
        i=0;

+       if (g_debugMode==2) prnt("DEBUG STT: Starting STT trim - start: %d, datalen: %d ",dataloc, datalen);            
+

        // warning - overwriting buffer given with raw wave data with ST removed...
        while ( dataloc < bufsize-(clk/2) ) {
                //compensate for long high at end of ST not being high due to signal loss... (and we cut out the start of wave high part)
        // warning - overwriting buffer given with raw wave data with ST removed...
        while ( dataloc < bufsize-(clk/2) ) {
                //compensate for long high at end of ST not being high due to signal loss... (and we cut out the start of wave high part)


@@ -1695,11 +1781,12 @@ bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
                                if (i+newloc < dataloc)
                                        buffer[i+newloc] = buffer[dataloc];
 
                                if (i+newloc < dataloc)
                                        buffer[i+newloc] = buffer[dataloc];
 

-                               dataloc++;                              
+                               dataloc++;

                        }
                }
                newloc += i;
                //skip next ST  -  we just assume it will be there from now on...
                        }
                }
                newloc += i;
                //skip next ST  -  we just assume it will be there from now on...

+               if (g_debugMode==2) prnt("DEBUG STT: skipping STT at %d to %d", dataloc, dataloc+(clk*4));

                dataloc += clk*4;
        }
        *size = newloc;
                dataloc += clk*4;
        }
        *size = newloc;