]> git.zerfleddert.de Git - proxmark3-svn/blobdiff - common/lfdemod.c
lf t55xx and some lf demod fixes/adjustments
[proxmark3-svn] / common / lfdemod.c
index 32feab6a6589934fd7cb291b883337915e7a027d..063c8a741173d2cc3cb5b615ec4e7b2ac1553994 100644 (file)
@@ -407,12 +407,12 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
                        if (currSample < (fclow-2)){            //0-5 = garbage noise
                                //do nothing with extra garbage
                        } else if (currSample < (fchigh-1)) { //6-8 = 8 sample waves
-                               if (LastSample > (fchigh-2) && preLastSample < (fchigh-1)){
+                               if (LastSample > (fchigh-2) && (preLastSample < (fchigh-1) || preLastSample     == 0 )){
                                        dest[numBits-1]=1;  //correct last 9 wave surrounded by 8 waves
                                }
                                dest[numBits++]=1;
 
-                       } else if (currSample > (fchigh+1) && !numBits) { //12 + and first bit = garbage 
+                       } 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
                                dest[numBits++]=1;
@@ -439,12 +439,16 @@ size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
                
                //if lastval was 1, we have a 1->0 crossing
                if (dest[idx-1]==1) {
-                       if (!numBits && n < rfLen/fclow) {
-                               n=0;
-                               lastval = dest[idx];
-                               continue;
+                       if (!numBits) {
+                               if (n < rfLen/fclow) {
+                                       n=0;
+                                       lastval = dest[idx];
+                                       continue;
+                               }
+                               n = (n * fclow + rfLen/4) / rfLen;
+                       } else {
+                               n = (n * fclow + rfLen/2) / rfLen;
                        }
-                       n = (n * fclow + rfLen/2) / rfLen;
                } else {// 0->1 crossing 
                        //test first bitsample too small
                        if (!numBits && n < rfLen/fchigh) {
@@ -703,15 +707,26 @@ int PyramiddemodFSK(uint8_t *dest, size_t *size)
        return (int)startIdx;
 }
 
+/*
+void dummy(char *fmt, ...){}
+
+#ifndef ON_DEVICE
+#include "ui.h"
+#define prnt PrintAndLog
+#else 
+
+#define prnt dummy
+#endif
+*/
 // by marshmellow
 // to detect a wave that has heavily clipped (clean) samples
 uint8_t DetectCleanAskWave(uint8_t dest[], size_t size, uint8_t high, uint8_t low)
 {
        uint16_t allPeaks=1;
        uint16_t cntPeaks=0;
-       size_t loopEnd = 512+60;
+       size_t loopEnd = 512+160;
        if (loopEnd > size) loopEnd = size;
-       for (size_t i=60; i<loopEnd; i++){
+       for (size_t i=160; i<loopEnd; i++){
                if (dest[i]>low && dest[i]<high) 
                        allPeaks=0;
                else
@@ -722,7 +737,6 @@ uint8_t DetectCleanAskWave(uint8_t dest[], size_t size, uint8_t high, uint8_t lo
        }
        return allPeaks;
 }
-
 // by marshmellow
 // to help detect clocks on heavily clipped samples
 // based on count of low to low
@@ -730,7 +744,7 @@ int DetectStrongAskClock(uint8_t dest[], size_t size, uint8_t high, uint8_t low)
 {
        uint8_t fndClk[] = {8,16,32,40,50,64,128};
        size_t startwave;
-       size_t i = 0;
+       size_t i = 100;
        size_t minClk = 255;
                // get to first full low to prime loop and skip incomplete first pulse
        while ((dest[i] < high) && (i < size))
@@ -753,6 +767,7 @@ int DetectStrongAskClock(uint8_t dest[], size_t size, uint8_t high, uint8_t low)
                        minClk = i - startwave;
        }
        // set clock
+       //prnt("minClk: %d",minClk);
        for (uint8_t clkCnt = 0; clkCnt<7; clkCnt++) {
                if (minClk >= fndClk[clkCnt]-(fndClk[clkCnt]/8) && minClk <= fndClk[clkCnt]+1)
                        return fndClk[clkCnt];
@@ -770,8 +785,8 @@ int DetectASKClock(uint8_t dest[], size_t size, int *clock, int maxErr)
        uint8_t clk[] = {255,8,16,32,40,50,64,100,128,255};
        uint8_t clkEnd = 9;
        uint8_t loopCnt = 255;  //don't need to loop through entire array...
-       if (size <= loopCnt) return -1; //not enough samples
-
+       if (size <= loopCnt+60) return -1; //not enough samples
+       size -= 60; //sometimes there is a strange end wave - filter out this....
        //if we already have a valid clock
        uint8_t clockFnd=0;
        for (;i<clkEnd;++i)
@@ -796,7 +811,6 @@ int DetectASKClock(uint8_t dest[], size_t size, int *clock, int maxErr)
                        }
                }
        }
-       
        uint8_t ii;
        uint8_t clkCnt, tol = 0;
        uint16_t bestErr[]={1000,1000,1000,1000,1000,1000,1000,1000,1000};
@@ -838,7 +852,7 @@ int DetectASKClock(uint8_t dest[], size_t size, int *clock, int maxErr)
                        }
                        //if we found no errors then we can stop here and a low clock (common clocks)
                        //  this is correct one - return this clock
-                                       //PrintAndLog("DEBUG: clk %d, err %d, ii %d, i %d",clk[clkCnt],errCnt,ii,i);
+                                       //prnt("DEBUG: clk %d, err %d, ii %d, i %d",clk[clkCnt],errCnt,ii,i);
                        if(errCnt==0 && clkCnt<7) { 
                                if (!clockFnd) *clock = clk[clkCnt];
                                return ii;
@@ -874,7 +888,7 @@ int DetectPSKClock(uint8_t dest[], size_t size, int clock)
        uint8_t clk[]={255,16,32,40,50,64,100,128,255}; //255 is not a valid clock
        uint16_t loopCnt = 4096;  //don't need to loop through entire array...
        if (size == 0) return 0;
-       if (size<loopCnt) loopCnt = size;
+       if (size<loopCnt) loopCnt = size-20;
 
        //if we already have a valid clock quit
        size_t i=1;
@@ -888,17 +902,17 @@ int DetectPSKClock(uint8_t dest[], size_t size, int clock)
        uint16_t peaksdet[]={0,0,0,0,0,0,0,0,0};
        fc = countFC(dest, size, 0);
        if (fc!=2 && fc!=4 && fc!=8) return -1;
-       //PrintAndLog("DEBUG: FC: %d",fc);
+       //prnt("DEBUG: FC: %d",fc);
 
        //find first full wave
-       for (i=0; i<loopCnt; i++){
+       for (i=160; i<loopCnt; i++){
                if (dest[i] < dest[i+1] && dest[i+1] >= dest[i+2]){
                        if (waveStart == 0) {
                                waveStart = i+1;
-                               //PrintAndLog("DEBUG: waveStart: %d",waveStart);
+                               //prnt("DEBUG: waveStart: %d",waveStart);
                        } else {
                                waveEnd = i+1;
-                               //PrintAndLog("DEBUG: waveEnd: %d",waveEnd);
+                               //prnt("DEBUG: waveEnd: %d",waveEnd);
                                waveLenCnt = waveEnd-waveStart;
                                if (waveLenCnt > fc){
                                        firstFullWave = waveStart;
@@ -909,7 +923,7 @@ int DetectPSKClock(uint8_t dest[], size_t size, int clock)
                        }
                }
        }
-       //PrintAndLog("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);
+       //prnt("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);
        
        //test each valid clock from greatest to smallest to see which lines up
        for(clkCnt=7; clkCnt >= 1 ; clkCnt--){
@@ -917,7 +931,7 @@ int DetectPSKClock(uint8_t dest[], size_t size, int clock)
                waveStart = 0;
                errCnt=0;
                peakcnt=0;
-               //PrintAndLog("DEBUG: clk: %d, lastClkBit: %d",clk[clkCnt],lastClkBit);
+               //prnt("DEBUG: clk: %d, lastClkBit: %d",clk[clkCnt],lastClkBit);
 
                for (i = firstFullWave+fullWaveLen-1; i < loopCnt-2; i++){
                        //top edge of wave = start of new wave 
@@ -930,7 +944,7 @@ int DetectPSKClock(uint8_t dest[], size_t size, int clock)
                                        waveLenCnt = waveEnd-waveStart;
                                        if (waveLenCnt > fc){ 
                                                //if this wave is a phase shift
-                                               //PrintAndLog("DEBUG: phase shift at: %d, len: %d, nextClk: %d, ii: %d, fc: %d",waveStart,waveLenCnt,lastClkBit+clk[clkCnt]-tol,ii+1,fc);
+                                               //prnt("DEBUG: phase shift at: %d, len: %d, nextClk: %d, ii: %d, fc: %d",waveStart,waveLenCnt,lastClkBit+clk[clkCnt]-tol,ii+1,fc);
                                                if (i+1 >= lastClkBit + clk[clkCnt] - tol){ //should be a clock bit
                                                        peakcnt++;
                                                        lastClkBit+=clk[clkCnt];
@@ -959,11 +973,50 @@ int DetectPSKClock(uint8_t dest[], size_t size, int clock)
                if (peaksdet[i] > peaksdet[best]) {
                        best = i;
                }
-               //PrintAndLog("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best]);
+               //prnt("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best]);
        }
        return clk[best];
 }
 
+int DetectStrongNRZClk(uint8_t *dest, size_t size, int peak, int low){
+       //find shortest transition from high to low
+       size_t i = 0;
+       size_t transition1 = 0;
+       int lowestTransition = 255;
+       uint8_t lastWasHigh=0;
+       //find first valid beginning of a high/low wave
+       if (dest[i] >= peak) {
+               for (; i < size; i++) {
+                       if (dest[i] <= low) break;
+               }
+               lastWasHigh=0;
+       } else if (dest[i] <= low) {
+               for (; i < size; i++) {
+                       if (dest[i] >= peak) break;
+               }
+               lastWasHigh=1;  
+       } else {
+               for (; i < size; i++) {
+                       if (dest[i] >= peak || dest[i] <= low) {
+                               lastWasHigh = (dest[i] >= peak);
+                               break;
+                       }
+               }
+       }
+       if (i==size) return 0;
+       transition1 = i;
+
+       for (;i < size; i++) {
+               if ((dest[i] >= peak && !lastWasHigh) || (dest[i] <= low && lastWasHigh)) {
+                       lastWasHigh = (dest[i] >= peak);
+                       if (i-transition1 < lowestTransition) lowestTransition = i-transition1;
+                       transition1 = i;
+               }
+       }
+       if (lowestTransition == 255) lowestTransition = 0;
+       return lowestTransition;
+}
+
 //by marshmellow
 //detect nrz clock by reading #peaks vs no peaks(or errors)
 int DetectNRZClock(uint8_t dest[], size_t size, int clock)
@@ -972,8 +1025,7 @@ int DetectNRZClock(uint8_t dest[], size_t size, int clock)
        uint8_t clk[]={8,16,32,40,50,64,100,128,255};
        size_t loopCnt = 4096;  //don't need to loop through entire array...
        if (size == 0) return 0;
-       if (size<loopCnt) loopCnt = size;
-
+       if (size<loopCnt) loopCnt = size-20;
        //if we already have a valid clock quit
        for (; i < 8; ++i)
                if (clk[i] == clock) return clock;
@@ -982,38 +1034,80 @@ int DetectNRZClock(uint8_t dest[], size_t size, int clock)
        int peak, low;
        if (getHiLo(dest, loopCnt, &peak, &low, 75, 75) < 1) return 0;
 
-       //PrintAndLog("DEBUG: peak: %d, low: %d",peak,low);
+       int lowestTransition = DetectStrongNRZClk(dest, size-20, peak, low);
+       //prnt("DEBUG: peak: %d, low: %d",peak,low);
        size_t ii;
        uint8_t clkCnt;
        uint8_t tol = 0;
-       uint16_t peakcnt=0;
-       uint16_t peaksdet[]={0,0,0,0,0,0,0,0};
-       uint16_t maxPeak=0;
+       uint16_t smplCnt = 0;
+       int16_t peakcnt = 0;
+       int16_t peaksdet[] = {0,0,0,0,0,0,0,0};
+       uint16_t maxPeak = 255;
+       uint8_t firstpeak = 0;
        //test for large clipped waves
        for (i=0; i<loopCnt; i++){
                if (dest[i] >= peak || dest[i] <= low){
-                       peakcnt++;
+                       if (!firstpeak) continue;
+                       smplCnt++;
                } else {
-                       if (peakcnt>0 && maxPeak < peakcnt){
-                               maxPeak = peakcnt;
+                       firstpeak=1;
+                       if (smplCnt > 6 ){
+                               if (maxPeak > smplCnt){
+                                       maxPeak = smplCnt;
+                                       //prnt("maxPk: %d",maxPeak);
+                               }
+                               peakcnt++;
+                               //prnt("maxPk: %d, smplCnt: %d, peakcnt: %d",maxPeak,smplCnt,peakcnt);
+                               smplCnt=0;
                        }
-                       peakcnt=0;
                }
        }
+       uint8_t samePeak=0;
+       uint8_t errBitHigh=0;
        peakcnt=0;
        //test each valid clock from smallest to greatest to see which lines up
        for(clkCnt=0; clkCnt < 8; ++clkCnt){
-               //ignore clocks smaller than largest peak
-               if (clk[clkCnt]<maxPeak) continue;
-
+               //ignore clocks smaller than smallest peak
+               if (clk[clkCnt] < maxPeak - (clk[clkCnt]/4)) continue;
                //try lining up the peaks by moving starting point (try first 256)
-               for (ii=0; ii< loopCnt; ++ii){
+               for (ii=20; ii < loopCnt; ++ii){
                        if ((dest[ii] >= peak) || (dest[ii] <= low)){
                                peakcnt=0;
-                               // now that we have the first one lined up test rest of wave array
-                               for (i=0; i < ((int)((size-ii-tol)/clk[clkCnt])-1); ++i){
-                                       if (dest[ii+(i*clk[clkCnt])]>=peak || dest[ii+(i*clk[clkCnt])]<=low){
-                                               peakcnt++;
+                               uint8_t bitHigh =0;
+                               uint8_t ignoreCnt = 0;
+                               uint8_t ignoreWindow = 4;
+                               int lastBit = ii-clk[clkCnt]; 
+                               //loop through to see if this start location works
+                               for (i = ii; i < size-20; ++i) {
+                                       // if we are at a clock bit
+                                       if ((i >= lastBit + clk[clkCnt] - tol) && (i <= lastBit + clk[clkCnt] + tol)) {
+                                               //test high/low
+                                               if (dest[i] >= peak || dest[i] <= low) {
+                                                       if (samePeak) peakcnt--;
+                                                       bitHigh=1;
+                                                       peakcnt++;
+                                                       errBitHigh = 0;
+                                                       ignoreCnt = ignoreWindow;
+                                                       lastBit += clk[clkCnt];
+                                                       samePeak = 1;
+                                               } else if (i == lastBit + clk[clkCnt] + tol) {
+                                                       lastBit += clk[clkCnt];
+                                                       samePeak = 0;
+                                               }
+                                       //else if not a clock bit and no peaks
+                                       } else if (dest[i] < peak && dest[i] > low){
+                                               samePeak = 0;
+                                               if (ignoreCnt==0){
+                                                       bitHigh=0;
+                                                       if (errBitHigh==1) peakcnt--;
+                                                       errBitHigh=0;
+                                               } else {
+                                                       ignoreCnt--;
+                                               }
+                                               // else if not a clock bit but we have a peak
+                                       } else if ((dest[i]>=peak || dest[i]<=low) && (bitHigh==0)) {
+                                               //error bar found no clock...
+                                               errBitHigh=1;
                                        }
                                }
                                if(peakcnt>peaksdet[clkCnt]) {
@@ -1027,9 +1121,14 @@ int DetectNRZClock(uint8_t dest[], size_t size, int clock)
        for (iii=7; iii > 0; iii--){
                if (peaksdet[iii] > peaksdet[best]){
                        best = iii;
+               } else if (peaksdet[iii] == peaksdet[best] && lowestTransition){
+                       if (clk[iii] > (lowestTransition - (clk[iii]/8)) && clk[iii] < (lowestTransition + (clk[iii]/8))){
+                               best = iii;
+                       }
                }
-               //PrintAndLog("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best]);
+               //prnt("DEBUG: Clk: %d, peaks: %d, maxPeak: %d, bestClk: %d, lowestTrs: %d",clk[iii],peaksdet[iii],maxPeak, clk[best], lowestTransition);
        }
+
        return clk[best];
 }
 
@@ -1089,123 +1188,37 @@ int indala26decode(uint8_t *bitStream, size_t *size, uint8_t *invert)
        return (int) startidx;
 }
 
-// by marshmellow - demodulate NRZ wave (both similar enough)
+// by marshmellow - demodulate NRZ wave
 // peaks invert bit (high=1 low=0) each clock cycle = 1 bit determined by last peak
-// there probably is a much simpler way to do this.... 
-int nrzRawDemod(uint8_t *dest, size_t *size, int *clk, int *invert, int maxErr)
-{
+int nrzRawDemod(uint8_t *dest, size_t *size, int *clk, int *invert){
        if (justNoise(dest, *size)) return -1;
        *clk = DetectNRZClock(dest, *size, *clk);
        if (*clk==0) return -2;
        size_t i, gLen = 4096;
-       if (gLen>*size) gLen = *size;
+       if (gLen>*size) gLen = *size-20;
        int high, low;
        if (getHiLo(dest, gLen, &high, &low, 75, 75) < 1) return -3; //25% fuzz on high 25% fuzz on low
-       int lastBit = 0;  //set first clock check
-       size_t iii = 0, bitnum = 0; //bitnum counter
-       uint16_t errCnt = 0, MaxBits = 1000;
-       size_t bestErrCnt = maxErr+1;
-       size_t bestPeakCnt = 0, bestPeakStart = 0;
-       uint8_t bestFirstPeakHigh=0, firstPeakHigh=0, curBit=0, bitHigh=0, errBitHigh=0;
-       uint8_t tol = 1;  //clock tolerance adjust - waves will be accepted as within the clock if they fall + or - this value + clock from last valid wave
-       uint16_t peakCnt=0;
-       uint8_t ignoreWindow=4;
-       uint8_t ignoreCnt=ignoreWindow; //in case of noise near peak
-       //loop to find first wave that works - align to clock
-       for (iii=0; iii < gLen; ++iii){
-               if ((dest[iii]>=high) || (dest[iii]<=low)){
-                       if (dest[iii]>=high) firstPeakHigh=1;
-                       else firstPeakHigh=0;
-                       lastBit=iii-*clk;
-                       peakCnt=0;
-                       errCnt=0;
-                       //loop through to see if this start location works
-                       for (i = iii; i < *size; ++i) {
-                               // if we are at a clock bit
-                               if ((i >= lastBit + *clk - tol) && (i <= lastBit + *clk + tol)) {
-                                       //test high/low
-                                       if (dest[i] >= high || dest[i] <= low) {
-                                               bitHigh = 1;
-                                               peakCnt++;
-                                               errBitHigh = 0;
-                                               ignoreCnt = ignoreWindow;
-                                               lastBit += *clk;
-                                       } else if (i == lastBit + *clk + tol) {
-                                               lastBit += *clk;
-                                       }
-                               //else if no bars found
-                               } else if (dest[i] < high && dest[i] > low){
-                                       if (ignoreCnt==0){
-                                               bitHigh=0;
-                                               if (errBitHigh==1) errCnt++;
-                                               errBitHigh=0;
-                                       } else {
-                                               ignoreCnt--;
-                                       }
-                               } else if ((dest[i]>=high || dest[i]<=low) && (bitHigh==0)) {
-                                       //error bar found no clock...
-                                       errBitHigh=1;
-                               }
-                               if (((i-iii) / *clk)>=MaxBits) break;
-                       }
-                       //we got more than 64 good bits and not all errors
-                       if (((i-iii) / *clk) > 64 && (errCnt <= (maxErr))) {
-                               //possible good read
-                               if (!errCnt || peakCnt > bestPeakCnt){
-                                       bestFirstPeakHigh=firstPeakHigh;
-                                       bestErrCnt = errCnt;
-                                       bestPeakCnt = peakCnt;
-                                       bestPeakStart = iii;
-                                       if (!errCnt) break;  //great read - finish
-                               }
-                       }
-               }
+       
+       uint8_t bit=0;
+       //convert wave samples to 1's and 0's
+       for(i=20; i < *size-20; i++){
+               if (dest[i] >= high) bit = 1;
+               if (dest[i] <= low)  bit = 0;
+               dest[i] = bit;
        }
-       //PrintAndLog("DEBUG: bestErrCnt: %d, maxErr: %d, bestStart: %d, bestPeakCnt: %d, bestPeakStart: %d",bestErrCnt,maxErr,bestStart,bestPeakCnt,bestPeakStart);
-       if (bestErrCnt > maxErr) return bestErrCnt;             
-
-       //best run is good enough set to best run and set overwrite BinStream
-       lastBit = bestPeakStart - *clk;
-       memset(dest, bestFirstPeakHigh^1, bestPeakStart / *clk);
-       bitnum += (bestPeakStart / *clk);
-       for (i = bestPeakStart; i < *size; ++i) {
-               // if expecting a clock bit
-               if ((i >= lastBit + *clk - tol) && (i <= lastBit + *clk + tol)) {
-                       // test high/low
-                       if (dest[i] >= high || dest[i] <= low) {
-                               peakCnt++;
-                               bitHigh = 1;
-                               errBitHigh = 0;
-                               ignoreCnt = ignoreWindow;
-                               curBit = *invert;
-                               if (dest[i] >= high) curBit ^= 1;
-                               dest[bitnum++] = curBit;
-                               lastBit += *clk;
-                       //else no bars found in clock area
-                       } else if (i == lastBit + *clk + tol) {
-                               dest[bitnum++] = curBit;
-                               lastBit += *clk;
-                       }
-               //else if no bars found
-               } else if (dest[i] < high && dest[i] > low){
-                       if (ignoreCnt == 0){
-                               bitHigh = 0;
-                               if (errBitHigh == 1){
-                                       dest[bitnum++] = 7;
-                                       errCnt++;
-                               }
-                               errBitHigh=0;
-                       } else {
-                               ignoreCnt--;
-                       }
-               } else if ((dest[i] >= high || dest[i] <= low) && (bitHigh == 0)) {
-                       //error bar found no clock...
-                       errBitHigh=1;
+       //now demod based on clock (rf/32 = 32 1's for one 1 bit, 32 0's for one 0 bit) 
+       size_t lastBit = 0;
+       size_t numBits = 0;
+       for(i=21; i < *size-20; i++) {
+               //if transition detected or large number of same bits - store the passed bits
+               if (dest[i] != dest[i-1] || (i-lastBit) == (10 * *clk)) {
+                       memset(dest+numBits, dest[i-1] ^ *invert, (i - lastBit + (*clk/4)) / *clk);
+                       numBits += (i - lastBit + (*clk/4)) / *clk;
+                       lastBit = i-1;
                }
-               if (bitnum >= MaxBits) break;
        }
-       *size = bitnum;
-       return bestErrCnt;
+       *size = numBits;
+       return 0;
 }
 
 //by marshmellow
@@ -1405,6 +1418,7 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
        uint16_t loopCnt = 4096;  //don't need to loop through entire array...
        if (*size<loopCnt) loopCnt = *size;
 
+       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;
@@ -1421,7 +1435,7 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
                        waveEnd = i+1;
                        //PrintAndLog("DEBUG: waveEnd: %d",waveEnd);
                        waveLenCnt = waveEnd-waveStart;
-                       if (waveLenCnt > fc && waveStart > fc){ //not first peak and is a large wave 
+                       if (waveLenCnt > fc && waveStart > fc && !(waveLenCnt > fc+2)){ //not first peak and is a large wave but not out of whack
                                lastAvgWaveVal = avgWaveVal/(waveLenCnt);
                                firstFullWave = waveStart;
                                fullWaveLen=waveLenCnt;
@@ -1434,14 +1448,21 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
                }
                avgWaveVal += dest[i+2];
        }
+       if (firstFullWave == 0) {
+               // no phase shift detected - could be all 1's or 0's - doesn't matter where we start
+               // so skip a little to ensure we are past any Start Signal
+               firstFullWave = 160;
+               memset(dest, curPhase, firstFullWave / *clock);
+       } else {
+               memset(dest, curPhase^1, firstFullWave / *clock);
+       }
+       //advance bits
+       numBits += (firstFullWave / *clock);
+       //set start of wave as clock align
+       lastClkBit = firstFullWave;
        //PrintAndLog("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);  
-       lastClkBit = firstFullWave; //set start of wave as clock align
        //PrintAndLog("DEBUG: clk: %d, lastClkBit: %d", *clock, lastClkBit);
        waveStart = 0;
-       size_t numBits=0;
-       //set skipped bits
-       memset(dest, curPhase^1, firstFullWave / *clock);
-       numBits += (firstFullWave / *clock);
        dest[numBits++] = curPhase; //set first read bit
        for (i = firstFullWave + fullWaveLen - 1; i < *size-3; i++){
                //top edge of wave = start of new wave 
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