speed up the em4x05 cmds by only getting 6k...

[proxmark3-svn] / common / lfdemod.c

diff --git a/common/lfdemod.c b/common/lfdemod.c
index d6c024fab9bfa872d9a210fa9dfb9334453e6aca..fbed6a9a8431fa913a4d56cba47b19297571ff4e 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 +170,23 @@ 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;
+}
+

 //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 +281,18 @@ 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]=127;
-               else if(BitStream[i]-BitStream[i-1]<=-20) //large jump down
-                       BitStream[i]=-127;
+                       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 +302,7 @@ 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;


@@ -464,10 +488,10 @@ int gProxII_Demod(uint8_t BitStream[], size_t *size)
                //return start position
                return (int) startIdx;
        }
                //return start position
                return (int) startIdx;
        }

-       return -5;
+       return -5; //spacer bits not found - not a valid gproxII

 }
 
 }
 

-//translate wave to 11111100000 (1 for each short wave 0 for each long wave)
+//translate wave to 11111100000 (1 for each short wave [higher freq] 0 for each long wave [lower freq])

 size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow)
 {
        size_t last_transition = 0;
 size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow)
 {
        size_t last_transition = 0;


@@ -480,41 +504,67 @@ 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
+
+       // jump to modulating data by finding the first 4 threshold crossings (or first 2 waves)
+       // in case you have junk or noise at the beginning of the trace...
+       uint8_t thresholdCnt = 0;
+       size_t waveSizeCnt = 0;
+       bool isAboveThreshold = dest[idx++] >= threshold_value;
+       for (; idx < size-20; idx++ ) {
+               if(dest[idx] < threshold_value && isAboveThreshold) {
+                       thresholdCnt++;
+                       if (thresholdCnt > 2 && waveSizeCnt < fchigh+1) break;                  
+                       isAboveThreshold = false;
+                       waveSizeCnt = 0;
+               } else if (dest[idx] >= threshold_value && !isAboveThreshold) {
+                       thresholdCnt++;
+                       if (thresholdCnt > 2 && waveSizeCnt < fchigh+1) break;                  
+                       isAboveThreshold = true;
+                       waveSizeCnt = 0;
+               } else {
+                       waveSizeCnt++;
+               }
+               if (thresholdCnt > 10) break;
+       }
+       if (g_debugMode == 2) prnt("threshold Count reached at %u",idx);

 
        // 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
        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

-       for(idx = 161; idx < size-20; idx++) {
+       //  (could also be fc/5 && fc/7 for fsk1 = 4-9)
+       for(; idx < size-20; idx++) {

                // threshold current value
 
                if (dest[idx] < threshold_value) dest[idx] = 0;
                else dest[idx] = 1;
 
                // Check for 0->1 transition
                // threshold current value
 
                if (dest[idx] < threshold_value) dest[idx] = 0;
                else dest[idx] = 1;
 
                // Check for 0->1 transition

-               if (dest[idx-1] < dest[idx]) { // 0 -> 1 transition
+               if (dest[idx-1] < dest[idx]) {

                        preLastSample = LastSample;
                        LastSample = currSample;
                        currSample = idx-last_transition;
                        preLastSample = LastSample;
                        LastSample = currSample;
                        currSample = idx-last_transition;

-                       if (currSample < (fclow-2)){            //0-5 = garbage noise (or 0-3)
+                       if (currSample < (fclow-2)) {                   //0-5 = garbage noise (or 0-3)

                                //do nothing with extra garbage
                                //do nothing with extra garbage

-                       } else if (currSample < (fchigh-1)) { //6-8 = 8 sample waves  or 3-6 = 5
-                               if (LastSample > (fchigh-2) && (preLastSample < (fchigh-1) || preLastSample     == 0 )){
-                                       dest[numBits-1]=1;  //correct previous 9 wave surrounded by 8 waves
+                       } 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))){
+                                       dest[numBits-1]=1;

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

-                       } else if (currSample > (fchigh) && !numBits) { //12 + and first bit = garbage 
-                               //do nothing with beginning garbage
-                       } else if (currSample == (fclow+1) && LastSample == (fclow-1)) { // had a 7 then a 9 should be two 8's
+                       } 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;
                                dest[numBits++]=1;

-                       } else {                                         //9+ = 10 sample waves
+                       } else {                                        //9+ = 10 sample waves (or 6+ = 7)

                                dest[numBits++]=0;
                        }
                        last_transition = idx;
                                dest[numBits++]=0;
                        }
                        last_transition = idx;


@@ -524,6 +574,7 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
 }
 
 //translate 11111100000 to 10
 }
 
 //translate 11111100000 to 10

+//rfLen = clock, fchigh = larger field clock, fclow = smaller field clock

 size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
                uint8_t invert, uint8_t fchigh, uint8_t fclow)
 {
 size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
                uint8_t invert, uint8_t fchigh, uint8_t fclow)
 {


@@ -533,8 +584,9 @@ size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
        uint32_t n=1;
        for( idx=1; idx < size; idx++) {
                n++;
        uint32_t n=1;
        for( idx=1; idx < size; idx++) {
                n++;

-               if (dest[idx]==lastval) continue; 
+               if (dest[idx]==lastval) continue; //skip until we hit a transition

                
                

+               //find out how many bits (n) we collected

                //if lastval was 1, we have a 1->0 crossing
                if (dest[idx-1]==1) {
                        n = (n * fclow + rfLen/2) / rfLen;
                //if lastval was 1, we have a 1->0 crossing
                if (dest[idx-1]==1) {
                        n = (n * fclow + rfLen/2) / rfLen;


@@ -543,6 +595,7 @@ size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
                }
                if (n == 0) n = 1;
 
                }
                if (n == 0) n = 1;
 

+               //add to our destination the bits we collected          

                memset(dest+numBits, dest[idx-1]^invert , n);
                numBits += n;
                n=0;
                memset(dest+numBits, dest[idx-1]^invert , n);
                numBits += n;
                n=0;


@@ -1365,10 +1418,10 @@ 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++)


@@ -1455,7 +1508,7 @@ 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;
+       size_t i=0, 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);
        uint8_t fc=0, fullWaveLen=0, tol=1;
        uint16_t errCnt=0, waveLenCnt=0;
        fc = countFC(dest, *size, 0);


@@ -1463,19 +1516,45 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
        //PrintAndLog("DEBUG: FC: %d",fc);
        *clock = DetectPSKClock(dest, *size, *clock);
        if (*clock == 0) return -1;
        //PrintAndLog("DEBUG: FC: %d",fc);
        *clock = DetectPSKClock(dest, *size, *clock);
        if (*clock == 0) return -1;

+       // jump to modulating data by finding the first 2 threshold crossings (or first 1 waves)
+       // in case you have junk or noise at the beginning of the trace...
+       uint8_t thresholdCnt = 0;
+       size_t waveSizeCnt = 0;
+       uint8_t threshold_value = 123; //-5
+       bool isAboveThreshold = dest[i++] >= threshold_value;
+       for (; i < *size-20; i++ ) {
+               if(dest[i] < threshold_value && isAboveThreshold) {
+                       thresholdCnt++;
+                       if (thresholdCnt > 2 && waveSizeCnt < fc+1) break;                      
+                       isAboveThreshold = false;
+                       waveSizeCnt = 0;
+               } else if (dest[i] >= threshold_value && !isAboveThreshold) {
+                       thresholdCnt++;
+                       if (thresholdCnt > 2 && waveSizeCnt < fc+1) break;                      
+                       isAboveThreshold = true;
+                       waveSizeCnt = 0;
+               } else {
+                       waveSizeCnt++;
+               }
+               if (thresholdCnt > 10) break;
+       }
+       if (g_debugMode == 2) prnt("DEBUG PSK: threshold Count reached at %u, count: %u",i, thresholdCnt);
+
+

        int avgWaveVal=0, lastAvgWaveVal=0;
        int avgWaveVal=0, lastAvgWaveVal=0;

+       waveStart = i+1;

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

-       for (i=0; i<loopCnt; i++){
+       for (; i<loopCnt; i++){

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

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


@@ -1495,8 +1574,8 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
        numBits += (firstFullWave / *clock);
        //set start of wave as clock align
        lastClkBit = firstFullWave;
        numBits += (firstFullWave / *clock);
        //set start of wave as clock align
        lastClkBit = firstFullWave;

-       //PrintAndLog("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);  
-       //PrintAndLog("DEBUG: clk: %d, lastClkBit: %d", *clock, lastClkBit);
+       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);

        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++){


@@ -1548,8 +1627,8 @@ 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;


@@ -1581,7 +1660,7 @@ 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


@@ -1627,6 +1706,8 @@ 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;


@@ -1640,7 +1721,7 @@ 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


@@ -1662,12 +1743,15 @@ 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) {


@@ -1675,11 +1759,23 @@ 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) ) {
        // 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... (we cut out the high part)
+               //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)

                if (buffer[dataloc]<high && buffer[dataloc]>low && buffer[dataloc+3]<high && buffer[dataloc+3]>low) {
                        for(i=0; i < clk/2-tol; ++i) {
                                buffer[dataloc+i] = high+5;
                if (buffer[dataloc]<high && buffer[dataloc]>low && buffer[dataloc+3]<high && buffer[dataloc+3]>low) {
                        for(i=0; i < clk/2-tol; ++i) {
                                buffer[dataloc+i] = high+5;


@@ -1690,11 +1786,12 @@ 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;
                        }
                }
                newloc += i;

-               //skip next ST
+               //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;