X-Git-Url: http://cvs.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/bf32dd923f3fbbfaa0932390fb1a771d03d0cf45..7aa24806f420d064f325a4b46d6b639095cc7e6b:/common/lfdemod.c

diff --git a/common/lfdemod.c b/common/lfdemod.c
index 4c0f3ad9..7e31f53d 100644
--- a/common/lfdemod.c
+++ b/common/lfdemod.c
@@ -9,9 +9,8 @@
 //-----------------------------------------------------------------------------
 
 #include <stdlib.h>
-#include <string.h>
 #include "lfdemod.h"
-#include "common.h"
+#include <string.h>
 
 //un_comment to allow debug print calls when used not on device
 void dummy(char *fmt, ...){}
@@ -69,7 +68,7 @@ uint8_t parityTest(uint32_t bits, uint8_t bitLen, uint8_t pType)
 
 //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 Always 1's), and binary Length (length to run) 
+//   Parity Type (1 for odd; 0 for even; 2 for Always 1's; 3 for Always 0'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;
@@ -81,10 +80,11 @@ size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t p
 		}
 		j--; // overwrite parity with next data
 		// if parity fails then return 0
-		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;			
+		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;
 		}
 		bitCnt+=(pLen-1);
 		parityWd = 0;
@@ -96,7 +96,8 @@ size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t p
 
 // by marshmellow
 // takes a array of binary values, length of bits per parity (includes parity bit),
-//   Parity Type (1 for odd; 0 for even; 2 Always 1's), and binary Length (length to run)
+//   Parity Type (1 for odd; 0 for even; 2 Always 1's; 3 Always 0's), and binary Length (length to run)
+//   Make sure *dest is long enough to store original sourceLen + #_of_parities_to_be_added
 size_t addParity(uint8_t *BitSource, uint8_t *dest, uint8_t sourceLen, uint8_t pLen, uint8_t pType)
 {
 	uint32_t parityWd = 0;
@@ -106,11 +107,14 @@ size_t addParity(uint8_t *BitSource, uint8_t *dest, uint8_t sourceLen, uint8_t p
 			parityWd = (parityWd << 1) | BitSource[word+bit];
 			dest[j++] = (BitSource[word+bit]);
 		}
+		
 		// if parity fails then return 0
-		if (pType == 2) { // then marker bit which should be a 1
-			dest[j++]=1;
-		} else {
-			dest[j++] = parityTest(parityWd, pLen-1, pType) ^ 1;
+		switch (pType) {
+			case 3: dest[j++]=0; break; // marker bit which should be a 0
+			case 2: dest[j++]=1; break; // marker bit which should be a 1
+			default: 
+				dest[j++] = parityTest(parityWd, pLen-1, pType) ^ 1;
+				break;
 		}
 		bitCnt += pLen;
 		parityWd = 0;
@@ -123,8 +127,7 @@ size_t addParity(uint8_t *BitSource, uint8_t *dest, uint8_t sourceLen, uint8_t p
 uint32_t bytebits_to_byte(uint8_t *src, size_t numbits)
 {
 	uint32_t num = 0;
-	for(int i = 0 ; i < numbits ; i++)
-	{
+	for(int i = 0 ; i < numbits ; i++) {
 		num = (num << 1) | (*src);
 		src++;
 	}
@@ -135,8 +138,7 @@ uint32_t bytebits_to_byte(uint8_t *src, size_t numbits)
 uint32_t bytebits_to_byteLSBF(uint8_t *src, size_t numbits)
 {
 	uint32_t num = 0;
-	for(int i = 0 ; i < numbits ; i++)
-	{
+	for(int i = 0 ; i < numbits ; i++) {
 		num = (num << 1) | *(src + (numbits-(i+1)));
 	}
 	return num;
@@ -218,6 +220,7 @@ int cleanAskRawDemod(uint8_t *BinStream, size_t *size, int clk, int invert, int
 				if (smplCnt > clk-(clk/4)-1) { //full clock
 					if (smplCnt > clk + (clk/4)+1) { //too many samples
 						errCnt++;
+						if (g_debugMode==2) prnt("DEBUG ASK: Modulation Error at: %u", i);
 						BinStream[bitCnt++]=7;
 					} else if (waveHigh) {
 						BinStream[bitCnt++] = invert;
@@ -256,13 +259,15 @@ int cleanAskRawDemod(uint8_t *BinStream, size_t *size, int clk, int invert, int
 //by marshmellow
 void askAmp(uint8_t *BitStream, size_t size)
 {
-	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;
+	uint8_t last = 128;
+	for(size_t i = 1; i < size; ++i){
+		if (BitStream[i]-BitStream[i-1] >= 30) //large jump up
+			last = 255;
+		else if(BitStream[i-1] - BitStream[i] >= 20) //large jump down
+			last = 0;
+		
+		BitStream[i] = last;
 	}
-	return;
 }
 
 //by marshmellow
@@ -274,7 +279,7 @@ 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 (g_debugMode==2) prnt("DEBUG: clk %d, beststart %d", *clk, start);
+	if (g_debugMode==2) prnt("DEBUG ASK: clk %d, beststart %d", *clk, start);
 
 	uint8_t initLoopMax = 255;
 	if (initLoopMax > *size) initLoopMax = *size;
@@ -287,20 +292,21 @@ int askdemod(uint8_t *BinStream, size_t *size, int *clk, int *invert, int maxErr
 	size_t errCnt = 0;
 	// if clean clipped waves detected run alternate demod
 	if (DetectCleanAskWave(BinStream, *size, high, low)) {
-		if (g_debugMode==2) prnt("DEBUG: Clean Wave Detected");
+		if (g_debugMode==2) prnt("DEBUG ASK: Clean Wave Detected - using clean wave demod");
 		errCnt = cleanAskRawDemod(BinStream, size, *clk, *invert, high, low);
 		if (askType) //askman
 			return manrawdecode(BinStream, size, 0);	
 		else //askraw
 			return errCnt;
 	}
+	if (g_debugMode==2) prnt("DEBUG ASK: Weak Wave Detected - using weak wave demod");
 
 	int lastBit;  //set first clock check - can go negative
 	size_t i, bitnum = 0;     //output counter
 	uint8_t midBit = 0;
 	uint8_t tol = 0;  //clock tolerance adjust - waves will be accepted as within the clock if they fall + or - this value + clock from last valid wave
 	if (*clk <= 32) tol = 1;    //clock tolerance may not be needed anymore currently set to + or - 1 but could be increased for poor waves or removed entirely
-	size_t MaxBits = 3072;
+	size_t MaxBits = 3072;    //max bits to collect
 	lastBit = start - *clk;
 
 	for (i = start; i < *size; ++i) {
@@ -311,6 +317,7 @@ int askdemod(uint8_t *BinStream, size_t *size, int *clk, int *invert, int maxErr
 				BinStream[bitnum++] = *invert ^ 1;
 			} else if (i-lastBit >= *clk+tol) {
 				if (bitnum > 0) {
+					if (g_debugMode==2) prnt("DEBUG ASK: Modulation Error at: %u", i);
 					BinStream[bitnum++]=7;
 					errCnt++;						
 				} 
@@ -458,10 +465,10 @@ int gProxII_Demod(uint8_t BitStream[], size_t *size)
 		//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;
@@ -483,8 +490,9 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
 
 	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 with anywhere
+	// 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++) {
 		// threshold current value
 
@@ -492,23 +500,24 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
 		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;
 			if (currSample < (fclow-2)){            //0-5 = garbage noise (or 0-3)
 				//do nothing with extra garbage
-			} else if (currSample < (fchigh-1)) { //6-8 = 8 sample waves  or 3-6 = 5
+			} 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 )){
-					dest[numBits-1]=1;  //correct previous 9 wave surrounded by 8 waves
+					dest[numBits-1]=1;
 				}
 				dest[numBits++]=1;
 
-			} else if (currSample > (fchigh) && !numBits) { //12 + and first bit = garbage 
+			} else if (currSample > (fchigh) && !numBits) { //12 + and first bit = unusable 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 == (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
+			} else {                                        //9+ = 10 sample waves (or 6+ = 7)
 				dest[numBits++]=0;
 			}
 			last_transition = idx;
@@ -518,6 +527,7 @@ size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow
 }
 
 //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)
 {
@@ -529,6 +539,7 @@ size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
 		n++;
 		if (dest[idx]==lastval) continue; 
 		
+		//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;
@@ -537,6 +548,7 @@ size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
 		}
 		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;
@@ -669,15 +681,33 @@ int VikingDemod_AM(uint8_t *dest, size_t *size) {
 	uint8_t preamble[] = {1,1,1,1,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
 	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
 	if (errChk == 0) return -4; //preamble not found
-	uint32_t checkCalc = bytebits_to_byte(dest+startIdx,8) ^ bytebits_to_byte(dest+startIdx+8,8) ^ bytebits_to_byte(dest+startIdx+16,8)
-	    ^ bytebits_to_byte(dest+startIdx+24,8) ^ bytebits_to_byte(dest+startIdx+32,8) ^ bytebits_to_byte(dest+startIdx+40,8) 
-	    ^ bytebits_to_byte(dest+startIdx+48,8) ^ bytebits_to_byte(dest+startIdx+56,8);
-	if ( checkCalc != 0xA8 ) return -5;
+	uint32_t checkCalc = bytebits_to_byte(dest+startIdx,8) ^ 
+						 bytebits_to_byte(dest+startIdx+8,8) ^ 
+						 bytebits_to_byte(dest+startIdx+16,8) ^ 
+						 bytebits_to_byte(dest+startIdx+24,8) ^ 
+						 bytebits_to_byte(dest+startIdx+32,8) ^ 
+						 bytebits_to_byte(dest+startIdx+40,8) ^ 
+						 bytebits_to_byte(dest+startIdx+48,8) ^ 
+						 bytebits_to_byte(dest+startIdx+56,8);
+	if ( checkCalc != 0xA8 ) return -5;	
 	if (*size != 64) return -6;
 	//return start position
 	return (int) startIdx;
 }
 
+// find presco preamble 0x10D in already demoded data
+int PrescoDemod(uint8_t *dest, size_t *size) {
+	//make sure buffer has data
+	if (*size < 64*2) return -2;
+
+	size_t startIdx = 0;
+	uint8_t preamble[] = {1,0,0,0,0,1,1,0,1,0,0,0,0,0,0,0,0,0,0,0};
+	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
+	if (errChk == 0) return -4; //preamble not found
+	//return start position
+	return (int) startIdx;
+}
+
 // Ask/Biphase Demod then try to locate an ISO 11784/85 ID
 // BitStream must contain previously askrawdemod and biphasedemoded data
 int FDXBdemodBI(uint8_t *dest, size_t *size)
@@ -693,6 +723,39 @@ int FDXBdemodBI(uint8_t *dest, size_t *size)
 	return (int)startIdx;
 }
 
+// ASK/Diphase fc/64 (inverted Biphase)
+// Note: this i s not a demod, this is only a detection
+// the parameter *dest needs to be demoded before call
+int JablotronDemod(uint8_t *dest, size_t *size){
+	//make sure buffer has enough data
+	if (*size < 64) return -1;
+
+	size_t startIdx = 0;
+	// 0xFFFF preamble, 64bits
+	uint8_t preamble[] = {
+		        1,1,1,1,
+	            1,1,1,1,
+				1,1,1,1,
+				1,1,1,1,
+				0
+		};
+
+	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
+	if (errChk == 0) return -4; //preamble not found
+	if (*size != 64) return -3;
+	
+	uint8_t checkchksum = 0;
+	for (int i=16; i < 56; i += 8) {
+		checkchksum += bytebits_to_byte(dest+startIdx+i,8);
+	}
+	checkchksum ^= 0x3A;
+
+	uint8_t crc = bytebits_to_byte(dest+startIdx+56, 8);
+	
+	if ( checkchksum != crc ) return -5;	
+	return (int)startIdx;
+}
+
 // by marshmellow
 // FSK Demod then try to locate an AWID ID
 int AWIDdemodFSK(uint8_t *dest, size_t *size)
@@ -736,6 +799,19 @@ int PyramiddemodFSK(uint8_t *dest, size_t *size)
 	return (int)startIdx;
 }
 
+// find nedap preamble in already demoded data
+int NedapDemod(uint8_t *dest, size_t *size) {
+	//make sure buffer has data
+	if (*size < 128) return -3;
+
+	size_t startIdx = 0;
+	//uint8_t preamble[] = {1,1,1,1,1,1,1,1,1,0,0,0,1};
+	uint8_t preamble[] = {1,1,1,1,1,1,1,1,1,0};
+	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
+	if (errChk == 0) return -4; //preamble not found
+	return (int) startIdx;
+}
+
 // 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)
@@ -1199,7 +1275,7 @@ int indala26decode(uint8_t *bitStream, size_t *size, uint8_t *invert)
 	return (int) startidx;
 }
 
-// by marshmellow - demodulate NRZ wave
+// by marshmellow - demodulate NRZ wave - requires a read with strong signal
 // peaks invert bit (high=1 low=0) each clock cycle = 1 bit determined by last peak
 int nrzRawDemod(uint8_t *dest, size_t *size, int *clk, int *invert){
 	if (justNoise(dest, *size)) return -1;
@@ -1476,8 +1552,8 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
 	numBits += (firstFullWave / *clock);
 	//set start of wave as clock align
 	lastClkBit = firstFullWave;
-	//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++){
@@ -1518,3 +1594,166 @@ int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
 	*size = numBits;
 	return errCnt;
 }
+
+//by marshmellow
+//attempt to identify a Sequence Terminator in ASK modulated raw wave
+bool DetectST(uint8_t buffer[], size_t *size, int *foundclock) {
+	size_t bufsize = *size;
+	//need to loop through all samples and identify our clock, look for the ST pattern
+	uint8_t fndClk[] = {8,16,32,40,50,64,128};
+	int clk = 0; 
+	int tol = 0;
+	int i, j, skip, start, end, low, high, minClk, waveStart;
+	bool complete = false;
+	int tmpbuff[bufsize / 64];
+	int waveLen[bufsize / 64];
+	size_t testsize = (bufsize < 512) ? bufsize : 512;
+	int phaseoff = 0;
+	high = low = 128;
+	memset(tmpbuff, 0, sizeof(tmpbuff));
+
+	if ( getHiLo(buffer, testsize, &high, &low, 80, 80) == -1 ) {
+		if (g_debugMode==2) prnt("DEBUG STT: just noise detected - quitting");
+		return false; //just noise
+	}
+	i = 0;
+	j = 0;
+	minClk = 255;
+	// get to first full low to prime loop and skip incomplete first pulse
+	while ((buffer[i] < high) && (i < bufsize))
+		++i;
+	while ((buffer[i] > low) && (i < bufsize))
+		++i;
+	skip = i;
+
+	// populate tmpbuff buffer with pulse lengths
+	while (i < bufsize) {
+		// measure from low to low
+		while ((buffer[i] > low) && (i < bufsize))
+			++i;
+		start= i;
+		while ((buffer[i] < high) && (i < bufsize))
+			++i;
+		//first high point for this wave
+		waveStart = i;
+		while ((buffer[i] > low) && (i < bufsize))
+			++i;
+		if (j >= (bufsize/64)) {
+			break;
+		}
+		waveLen[j] = i - waveStart; //first high to first low
+		tmpbuff[j++] = i - start;
+		if (i-start < minClk && i < bufsize) {
+			minClk = i - start;
+		}
+	}
+	// set clock  - might be able to get this externally and remove this work...
+	if (!clk) {
+		for (uint8_t clkCnt = 0; clkCnt<7; clkCnt++) {
+			tol = fndClk[clkCnt]/8;
+			if (minClk >= fndClk[clkCnt]-tol && minClk <= fndClk[clkCnt]+1) { 
+				clk=fndClk[clkCnt];
+				break;
+			}
+		}
+		// clock not found - ERROR
+		if (!clk) {
+			if (g_debugMode==2) prnt("DEBUG STT: clock not found - quitting");
+			return false;
+		}
+	} else tol = clk/8;
+
+	*foundclock = clk;
+
+	// look for Sequence Terminator - should be pulses of clk*(1 or 1.5), clk*2, clk*(1.5 or 2)
+	start = -1;
+	for (i = 0; i < j - 4; ++i) {
+		skip += tmpbuff[i];
+		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
+						start = i + 3;
+						break;
+					}
+				}
+			}
+		}
+	}
+	// first ST not found - ERROR
+	if (start < 0) {
+		if (g_debugMode==2) prnt("DEBUG STT: first STT not found - quitting");
+		return false;
+	}
+	if (waveLen[i+2] > clk*1+tol)
+		phaseoff = 0;
+	else
+		phaseoff = clk/2;
+	
+	// skip over the remainder of ST
+	skip += clk*7/2; //3.5 clocks from tmpbuff[i] = end of st - also aligns for ending point
+
+	// now do it again to find the end
+	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+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
+						complete = true;
+						break;
+					}
+				}
+			}
+		}
+	}
+	end -= phaseoff;
+	//didn't find second ST - ERROR
+	if (!complete) {
+		if (g_debugMode==2) prnt("DEBUG STT: second STT not found - quitting");
+		return false;
+	}
+	if (g_debugMode==2) prnt("DEBUG STT: start of data: %d end of data: %d, datalen: %d, clk: %d, bits: %d, phaseoff: %d", skip, end, end-skip, clk, (end-skip)/clk, phaseoff);
+	//now begin to trim out ST so we can use normal demod cmds
+	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 (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 (g_debugMode==2) prnt("DEBUG STT: datalen is less than 1 full t55xx block - quitting");		
+		return false;
+	}
+	size_t dataloc = start;
+	size_t newloc = 0;
+	i=0;
+	// 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)
+		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;
+			}
+		}
+		for (i=0; i<datalen; ++i) {
+			if (i+newloc < bufsize) {
+				if (i+newloc < dataloc)
+					buffer[i+newloc] = buffer[dataloc];
+
+				dataloc++;				
+			}
+		}
+		newloc += i;
+		//skip next ST  -  we just assume it will be there from now on...
+		dataloc += clk*4;
+	}
+	*size = newloc;
+	return true;
+}