FIX: @marshmellow42 's fixes for enhanced STT and AskDemod. Now the "lf presco...

[proxmark3-svn] / common / lfdemod.c

//-----------------------------------------------------------------------------
// Copyright (C) 2014
//
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Low frequency demod/decode commands
//-----------------------------------------------------------------------------

#include <stdlib.h>
#include "lfdemod.h"
#include <string.h>

//un_comment to allow debug print calls when used not on device
void dummy(char *fmt, ...){}

#ifndef ON_DEVICE
#include "ui.h"
#include "cmdparser.h"
#include "cmddata.h"
#define prnt PrintAndLog
#else 
        uint8_t g_debugMode=0;
#define prnt dummy
#endif

//test samples are not just noise
uint8_t justNoise(uint8_t *bits, size_t size) {
        #define THRESHOLD 123
        uint8_t val = 1;
        for(size_t idx=0; idx < size && val ;idx++)
                val = bits[idx] < THRESHOLD;
        return val;
}

//by marshmellow
//get high and low values of a wave with passed in fuzz factor. also return noise test = 1 for passed or 0 for only noise
int getHiLo(uint8_t *BitStream, size_t size, int *high, int *low, uint8_t fuzzHi, uint8_t fuzzLo)
{
        *high=0;
        *low=255;
        // get high and low thresholds 
        for (size_t i=0; i < size; i++){
                if (BitStream[i] > *high) *high = BitStream[i];
                if (BitStream[i] < *low) *low = BitStream[i];
        }
        if (*high < 123) return -1; // just noise
        *high = ((*high-128)*fuzzHi + 12800)/100;
        *low = ((*low-128)*fuzzLo + 12800)/100;
        return 1;
}

// by marshmellow
// pass bits to be tested in bits, length bits passed in bitLen, and parity type (even=0 | odd=1) in pType
// returns 1 if passed
uint8_t parityTest(uint32_t bits, uint8_t bitLen, uint8_t pType)
{
        uint8_t ans = 0;
        for (uint8_t i = 0; i < bitLen; i++){
                ans ^= ((bits >> i) & 1);
        }
        //prnt("DEBUG: ans: %d, ptype: %d",ans,pType);
        return (ans == 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 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;
        size_t j = 0, bitCnt = 0;
        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]);
                }
                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: if (parityTest(parityWd, pLen, pType) == 0) { return 0; } break; //test parity
                }
                bitCnt += (pLen-1);
                parityWd = 0;
        }
        // if we got here then all the parities passed
        //return ID start index and size
        return bitCnt;
}

// 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; 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;
        size_t j = 0, bitCnt = 0;
        for (int word = 0; word < sourceLen; word+=pLen-1) {
                for (int bit=0; bit < pLen-1; bit++){
                        parityWd = (parityWd << 1) | BitSource[word+bit];
                        dest[j++] = (BitSource[word+bit]);
                }
                
                // if parity fails then return 0
                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;
        }
        // if we got here then all the parities passed
        //return ID start index and size
        return bitCnt;
}

uint32_t bytebits_to_byte(uint8_t *src, size_t numbits)
{
        uint32_t num = 0;
        for(int i = 0 ; i < numbits ; i++) {
                num = (num << 1) | (*src);
                src++;
        }
        return num;
}

//least significant bit first
uint32_t bytebits_to_byteLSBF(uint8_t *src, size_t numbits)
{
        uint32_t num = 0;
        for(int i = 0 ; i < numbits ; i++) {
                num = (num << 1) | *(src + (numbits-(i+1)));
        }
        return num;
}

//by marshmellow
//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){
                        //first index found
                        foundCnt++;
                        if (foundCnt == 1){
                                *startIdx = idx;
                        }
                        if (foundCnt == 2){
                                *size = idx - *startIdx;
                                return 1;
                        }
                }
        }
        return 0;
}

//by marshmellow
//takes 1s and 0s and searches for EM410x format - output EM ID
int Em410xDecode(uint8_t *BitStream, size_t *size, size_t *startIdx, uint32_t *hi, uint64_t *lo)
{
        //no arguments needed - built this way in case we want this to be a direct call from "data " cmds in the future
        //  otherwise could be a void with no arguments
        //set defaults
        uint32_t i = 0;
        if (BitStream[1]>1) return -1;  //allow only 1s and 0s

        // 111111111 bit pattern represent start of frame
        //  include 0 in front to help get start pos
        uint8_t preamble[] = {0,1,1,1,1,1,1,1,1,1};
        uint32_t idx = 0;
        uint32_t parityBits = 0;
        uint8_t errChk = 0;
        uint8_t FmtLen = 10;
        *startIdx = 0;
        errChk = preambleSearch(BitStream, preamble, sizeof(preamble), size, startIdx);
        if (errChk == 0 ) return -4;
        if (*size < 64) return -3;
        if (*size > 64) FmtLen = 22;
        *startIdx += 1; //get rid of 0 from preamble
        idx = *startIdx + 9;
        for (i=0; i<FmtLen; i++){ //loop through 10 or 22 sets of 5 bits (50-10p = 40 bits or 88 bits)
                parityBits = bytebits_to_byte(BitStream+(i*5)+idx,5);
                //check even parity - quit if failed
                if (parityTest(parityBits, 5, 0) == 0) return -5;
                //set uint64 with ID from BitStream
                for (uint8_t ii=0; ii<4; ii++){
                        *hi = (*hi << 1) | (*lo >> 63);
                        *lo = (*lo << 1) | (BitStream[(i*5)+ii+idx]);
                }
        }
        if (errChk != 0) return 1;
        //skip last 5 bit parity test for simplicity.
        // *size = 64 | 128;
        return 0;
}

//by marshmellow
//demodulates strong heavily clipped samples
int cleanAskRawDemod(uint8_t *BinStream, size_t *size, int clk, int invert, int high, int low)
{
        size_t bitCnt=0, smplCnt=0, errCnt=0;
        uint8_t waveHigh = 0;
        for (size_t i=0; i < *size; i++){
                if (BinStream[i] >= high && waveHigh){
                        smplCnt++;
                } else if (BinStream[i] <= low && !waveHigh){
                        smplCnt++;
                } else { //transition
                        if ((BinStream[i] >= high && !waveHigh) || (BinStream[i] <= low && waveHigh)){

                                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;
                                                BinStream[bitCnt++] = invert;
                                        } else if (!waveHigh) {
                                                BinStream[bitCnt++] = invert ^ 1;
                                                BinStream[bitCnt++] = invert ^ 1;
                                        }
                                        waveHigh ^= 1;  
                                        smplCnt = 0;
                                } else if (smplCnt > (clk/2) - (clk/4)-1) {
                                        if (waveHigh) {
                                                BinStream[bitCnt++] = invert;
                                        } else if (!waveHigh) {
                                                BinStream[bitCnt++] = invert ^ 1;
                                        }
                                        waveHigh ^= 1;  
                                        smplCnt = 0;
                                } else if (!bitCnt) {
                                        //first bit
                                        waveHigh = (BinStream[i] >= high);
                                        smplCnt = 1;
                                } else {
                                        smplCnt++;
                                        //transition bit oops
                                }
                        } else { //haven't hit new high or new low yet
                                smplCnt++;
                        }
                }
        }
        *size = bitCnt;
        return errCnt;
}

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

//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)
{
        if (*size==0) return -1;
        int start = DetectASKClock(BinStream, *size, clk, maxErr); //clock default
        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, amp %d", *clk, start, amp);

        uint8_t initLoopMax = 255;
        if (initLoopMax > *size) initLoopMax = *size;
        // Detect high and lows
        //25% clip in case highs and lows aren't clipped [marshmellow]
        int high, low;
        if (getHiLo(BinStream, initLoopMax, &high, &low, 75, 75) < 1) 
                return -2; //just noise

        size_t errCnt = 0;
        // if clean clipped waves detected run alternate demod
        if (DetectCleanAskWave(BinStream, *size, high, low)) {
                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);        
                //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;    //max bits to collect
        lastBit = start - *clk;

        for (i = start; i < *size; ++i) {
                if (i-lastBit >= *clk-tol){
                        if (BinStream[i] >= high) {
                                BinStream[bitnum++] = *invert;
                        } else if (BinStream[i] <= low) {
                                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++;                                               
                                } 
                        } else { //in tolerance - looking for peak
                                continue;
                        }
                        midBit = 0;
                        lastBit += *clk;
                } else if (i-lastBit >= (*clk/2-tol) && !midBit && !askType){
                        if (BinStream[i] >= high) {
                                BinStream[bitnum++] = *invert;
                        } else if (BinStream[i] <= low) {
                                BinStream[bitnum++] = *invert ^ 1;
                        } else if (i-lastBit >= *clk/2+tol) {
                                BinStream[bitnum] = BinStream[bitnum-1];
                                bitnum++;
                        } else { //in tolerance - looking for peak
                                continue;
                        }
                        midBit = 1;
                }
                if (bitnum >= MaxBits) break;
        }
        *size = bitnum;
        return errCnt;
}
//by marshmellow
//take 10 and 01 and manchester decode
//run through 2 times and take least errCnt
int manrawdecode(uint8_t * BitStream, size_t *size, uint8_t invert){
        uint16_t bitnum = 0, MaxBits = 512, errCnt = 0;
        size_t i, k;
        uint16_t bestErr = 1000, bestRun = 0;
        if (*size < 16) return -1;
        //find correct start position [alignment]
        for (k=0; k < 2; ++k){
                for (i=k; i<*size-3; i += 2)
                        if (BitStream[i] == BitStream[i+1])
                                errCnt++;

                if (bestErr > errCnt){
                        bestErr = errCnt;
                        bestRun = k;
                }
                errCnt=0;
        }
        //decode
        for (i=bestRun; i < *size-3; i += 2){
                if (BitStream[i] == 1 && (BitStream[i+1] == 0)){
                        BitStream[bitnum++] = invert;
                } else if ((BitStream[i] == 0) && BitStream[i+1] == 1){
                        BitStream[bitnum++] = invert^1;
                } else {
                        BitStream[bitnum++] = 7;
                }
                if (bitnum>MaxBits) break;
        }
        *size=bitnum;
        return bestErr;
}

uint32_t manchesterEncode2Bytes(uint16_t datain) {
        uint32_t output = 0;
        uint8_t curBit = 0;
        for (uint8_t i=0; i<16; i++) {
                curBit = (datain >> (15-i) & 1);
                output |= (1<<(((15-i)*2)+curBit));
        }
        return output;
}

//by marshmellow
//encode binary data into binary manchester 
int ManchesterEncode(uint8_t *BitStream, size_t size)
{
        size_t modIdx=20000, i=0;
        if (size>modIdx) return -1;
        for (size_t idx=0; idx < size; idx++){
                BitStream[idx+modIdx++] = BitStream[idx];
                BitStream[idx+modIdx++] = BitStream[idx]^1;
        }
        for (; i<(size*2); i++){
                BitStream[i] = BitStream[i+20000];
        }
        return i;
}

//by marshmellow
//take 01 or 10 = 1 and 11 or 00 = 0
//check for phase errors - should never have 111 or 000 should be 01001011 or 10110100 for 1010
//decodes biphase or if inverted it is AKA conditional dephase encoding AKA differential manchester encoding
int BiphaseRawDecode(uint8_t *BitStream, size_t *size, int offset, int invert)
{
        uint16_t bitnum = 0;
        uint16_t errCnt = 0;
        size_t i = offset;
        uint16_t MaxBits=512;
        //if not enough samples - error
        if (*size < 51) return -1;
        //check for phase change faults - skip one sample if faulty
        uint8_t offsetA = 1, offsetB = 1;
        for (; i<48; i+=2){
                if (BitStream[i+1]==BitStream[i+2]) offsetA=0; 
                if (BitStream[i+2]==BitStream[i+3]) offsetB=0;                                  
        }
        if (!offsetA && offsetB) offset++;
        for (i=offset; i<*size-3; i+=2){
                //check for phase error
                if (BitStream[i+1]==BitStream[i+2]) {
                        BitStream[bitnum++]=7;
                        errCnt++;
                }
                if((BitStream[i]==1 && BitStream[i+1]==0) || (BitStream[i]==0 && BitStream[i+1]==1)){
                        BitStream[bitnum++]=1^invert;
                } else if((BitStream[i]==0 && BitStream[i+1]==0) || (BitStream[i]==1 && BitStream[i+1]==1)){
                        BitStream[bitnum++]=invert;
                } else {
                        BitStream[bitnum++]=7;
                        errCnt++;
                }
                if(bitnum>MaxBits) break;
        }
        *size=bitnum;
        return errCnt;
}

// by marshmellow
// demod gProxIIDemod 
// error returns as -x 
// success returns start position in BitStream
// BitStream must contain previously askrawdemod and biphasedemoded data
int gProxII_Demod(uint8_t BitStream[], size_t *size)
{
        size_t startIdx=0;
        uint8_t preamble[] = {1,1,1,1,1,0};

        uint8_t errChk = preambleSearch(BitStream, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -3; //preamble not found
        if (*size != 96) return -2; //should have found 96 bits
        //check first 6 spacer bits to verify format
        if (!BitStream[startIdx+5] && !BitStream[startIdx+10] && !BitStream[startIdx+15] && !BitStream[startIdx+20] && !BitStream[startIdx+25] && !BitStream[startIdx+30]){
                //confirmed proper separator bits found
                //return start position
                return (int) startIdx;
        }
        return -5; //spacer bits not found - not a valid gproxII
}

//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 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
        uint8_t threshold_value = 123; 
        size_t preLastSample = 0;
        size_t LastSample = 0;
        size_t currSample = 0;
        // sync to first lo-hi transition, and threshold

        // Need to threshold first sample
        // skip 160 samples to allow antenna/samples to settle
        if(dest[160] < threshold_value) dest[0] = 0;
        else dest[0] = 1;

        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++) {
                // 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]) {
                        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)
                                //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;
                                }
                                dest[numBits++]=1;

                        } 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 (or 4 then a 6 should be two 5's)
                                dest[numBits++]=1;
                        } else {                                        //9+ = 10 sample waves (or 6+ = 7)
                                dest[numBits++]=0;
                        }
                        last_transition = idx;
                }
        }
        return numBits; //Actually, it returns the number of bytes, but each byte represents a bit: 1 or 0
}

//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)
{
        uint8_t lastval=dest[0];
        size_t idx=0;
        size_t numBits=0;
        uint32_t n=1;
        for( idx=1; idx < size; idx++) {
                n++;
                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;
                } else {// 0->1 crossing 
                        n = (n * fchigh + rfLen/2) / 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;
                lastval=dest[idx];
        }//end for
        // if valid extra bits at the end were all the same frequency - add them in
        if (n > rfLen/fchigh) {
                if (dest[idx-2]==1) {
                        n = (n * fclow + rfLen/2) / rfLen;
                } else {
                        n = (n * fchigh + rfLen/2) / rfLen;
                }
                memset(dest+numBits, dest[idx-1]^invert , n);
                numBits += n;
        }
        return numBits;
}

//by marshmellow  (from holiman's base)
// full fsk demod from GraphBuffer wave to decoded 1s and 0s (no mandemod)
int fskdemod(uint8_t *dest, size_t size, uint8_t rfLen, uint8_t invert, uint8_t fchigh, uint8_t fclow)
{
        // FSK demodulator
        size = fsk_wave_demod(dest, size, fchigh, fclow);
        size = aggregate_bits(dest, size, rfLen, invert, fchigh, fclow);
        return size;
}

// loop to get raw HID waveform then FSK demodulate the TAG ID from it
int HIDdemodFSK(uint8_t *dest, size_t *size, uint32_t *hi2, uint32_t *hi, uint32_t *lo)
{
        if (justNoise(dest, *size)) return -1;

        size_t numStart=0, size2 = *size, startIdx=0; 
        // FSK demodulator
        *size = fskdemod(dest, size2,50,1,10,8); //fsk2a
        if (*size < 96*2) return -2;
        // 00011101 bit pattern represent start of frame, 01 pattern represents a 0 and 10 represents a 1
        uint8_t preamble[] = {0,0,0,1,1,1,0,1};
        // find bitstring in array  
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -3; //preamble not found

        numStart = startIdx + sizeof(preamble);
        // final loop, go over previously decoded FSK data and manchester decode into usable tag ID
        for (size_t idx = numStart; (idx-numStart) < *size - sizeof(preamble); idx+=2){
                if (dest[idx] == dest[idx+1]){
                        return -4; //not manchester data
                }
                *hi2 = (*hi2<<1)|(*hi>>31);
                *hi = (*hi<<1)|(*lo>>31);
                //Then, shift in a 0 or one into low
                *lo <<= 1;
                if (dest[idx] && !dest[idx+1])  // 1 0
                        *lo |= 1;
                else // 0 1
                        *lo |= 0;
        }
        return (int)startIdx;
}

// loop to get raw paradox waveform then FSK demodulate the TAG ID from it
int ParadoxdemodFSK(uint8_t *dest, size_t *size, uint32_t *hi2, uint32_t *hi, uint32_t *lo)
{
        if (justNoise(dest, *size)) return -1;
        
        size_t numStart=0, size2 = *size, startIdx=0;
        // FSK demodulator
        *size = fskdemod(dest, size2,50,1,10,8); //fsk2a
        if (*size < 96) return -2;

        // 00001111 bit pattern represent start of frame, 01 pattern represents a 0 and 10 represents a 1
        uint8_t preamble[] = {0,0,0,0,1,1,1,1};

        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -3; //preamble not found

        numStart = startIdx + sizeof(preamble);
        // final loop, go over previously decoded FSK data and manchester decode into usable tag ID
        for (size_t idx = numStart; (idx-numStart) < *size - sizeof(preamble); idx+=2){
                if (dest[idx] == dest[idx+1]) 
                        return -4; //not manchester data
                *hi2 = (*hi2<<1)|(*hi>>31);
                *hi = (*hi<<1)|(*lo>>31);
                //Then, shift in a 0 or one into low
                if (dest[idx] && !dest[idx+1])  // 1 0
                        *lo=(*lo<<1)|1;
                else // 0 1
                        *lo=(*lo<<1)|0;
        }
        return (int)startIdx;
}

int IOdemodFSK(uint8_t *dest, size_t size)
{
        if (justNoise(dest, size)) return -1;
        //make sure buffer has data
        if (size < 66*64) return -2;
        // FSK demodulator
        size = fskdemod(dest, size, 64, 1, 10, 8);  // FSK2a RF/64 
        if (size < 65) return -3;  //did we get a good demod?
        //Index map
        //0           10          20          30          40          50          60
        //|           |           |           |           |           |           |
        //01234567 8 90123456 7 89012345 6 78901234 5 67890123 4 56789012 3 45678901 23
        //-----------------------------------------------------------------------------
        //00000000 0 11110000 1 facility 1 version* 1 code*one 1 code*two 1 ???????? 11
        //
        //XSF(version)facility:codeone+codetwo
        //Handle the data
        size_t startIdx = 0;
        uint8_t preamble[] = {0,0,0,0,0,0,0,0,0,1};
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), &size, &startIdx);
        if (errChk == 0) return -4; //preamble not found

        if (!dest[startIdx+8] && dest[startIdx+17]==1 && dest[startIdx+26]==1 && dest[startIdx+35]==1 && dest[startIdx+44]==1 && dest[startIdx+53]==1){
                //confirmed proper separator bits found
                //return start position
                return (int) startIdx;
        }
        return -5;
}

// by marshmellow
// find viking preamble 0xF200 in already demoded data
int VikingDemod_AM(uint8_t *dest, size_t *size) {
        //make sure buffer has data
        if (*size < 64*2) return -2;
        size_t startIdx = 0;
        uint8_t preamble[] = {1,1,1,1,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
        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;     
        if (*size != 64) return -6;
        //return start position
        return (int)startIdx;
}

// by iceman
// find Visa2000 preamble in already demoded data
int Visa2kDemod_AM(uint8_t *dest, size_t *size) {
        if (*size < 96*2) return -1; //make sure buffer has data
        size_t startIdx = 0;
        uint8_t preamble[] = {0,1,0,1,0,1,1,0,0,1,0,0,1,0,0,1,0,1,0,1,0,0,1,1,0,0,1,1,0,0,1,0};
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -2; //preamble not found
        if (*size != 96) return -3; //wrong demoded size
        //return start position
        return (int)startIdx;
}
// by iceman
// find Noralsy preamble in already demoded data
int NoralsyDemod_AM(uint8_t *dest, size_t *size) {
        if (*size < 96*2) return -1; //make sure buffer has data
        size_t startIdx = 0;
        uint8_t preamble[] = {1,0,1,1,1,0,1,1,0,0,0,0};
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -2; //preamble not found
        if (*size != 96) return -3; //wrong demoded size
        //return start position
        return (int)startIdx;
}
// find presco preamble 0x10D in already demoded data
int PrescoDemod(uint8_t *dest, size_t *size) {
        if (*size < 128*2) return -1; //make sure buffer has data
        size_t startIdx = 0;
        uint8_t preamble[] = {0,0,0,1,0,0,0,0,1,1,0,1,0,0,0,0,0,0,0,0,0,0,0};
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -2; //preamble not found
        if (*size != 128) return -3; //wrong demoded size
        //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) {
        if (*size < 128*2) return -1;   //make sure buffer has enough data
        size_t startIdx = 0;
        uint8_t preamble[] = {0,0,0,0,0,0,0,0,0,0,1};
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -2; //preamble not found
        if (*size != 128) return -3; //wrong demoded size
        //return start position
        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
// 0xFFFF preamble, 64bits
int JablotronDemod(uint8_t *dest, size_t *size){
        if (*size < 64*2) return -1;    //make sure buffer has enough data
        size_t startIdx = 0;
        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 -2; //preamble not found
        if (*size != 64) return -3; // wrong demoded size
        
        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)
{
        //make sure buffer has enough data
        if (*size < 96*50) return -1;

        if (justNoise(dest, *size)) return -2;

        // FSK demodulator
        *size = fskdemod(dest, *size, 50, 1, 10, 8);  // fsk2a RF/50 
        if (*size < 96) return -3;  //did we get a good demod?

        uint8_t preamble[] = {0,0,0,0,0,0,0,1};
        size_t startIdx = 0;
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -4; //preamble not found
        if (*size != 96) return -5;
        return (int)startIdx;
}

// by marshmellow
// FSK Demod then try to locate a Farpointe Data (pyramid) ID
int PyramiddemodFSK(uint8_t *dest, size_t *size)
{
        //make sure buffer has data
        if (*size < 128*50) return -5;

        //test samples are not just noise
        if (justNoise(dest, *size)) return -1;

        // FSK demodulator
        *size = fskdemod(dest, *size, 50, 1, 10, 8);  // fsk2a RF/50 
        if (*size < 128) return -2;  //did we get a good demod?

        uint8_t preamble[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1};
        size_t startIdx = 0;
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -4; //preamble not found
        if (*size != 128) return -3;
        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;
}

// Find IDTEC PSK1, RF  Preamble == 0x4944544B, Demodsize 64bits
// by iceman
int IdteckDemodPSK(uint8_t *dest, size_t *size) {
        //make sure buffer has data
        if (*size < 64*2) return -1;    
        size_t startIdx = 0;
        uint8_t preamble[] = {0,1,0,0,1,0,0,1,0,1,0,0,0,1,0,0,0,1,0,1,0,1,0,0,0,1,0,0,1,0,1,1};
        uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
        if (errChk == 0) return -2; //preamble not found
        if (*size != 64) return -3; // wrong demoded size
        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)
{
        bool allArePeaks = true;
        uint16_t cntPeaks=0;
        size_t loopEnd = 512+160;
        if (loopEnd > size) loopEnd = size;
        for (size_t i=160; i<loopEnd; i++){
                if (dest[i]>low && dest[i]<high) 
                        allArePeaks = false;
                else
                        cntPeaks++;
        }
        if (!allArePeaks){
                if (cntPeaks > 300) return true;
        }
        return allArePeaks;
}
// by marshmellow
// to help detect clocks on heavily clipped samples
// based on count of low to low
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 = 100;
        size_t minClk = 255;
                // get to first full low to prime loop and skip incomplete first pulse
        while ((dest[i] < high) && (i < size))
                ++i;
        while ((dest[i] > low) && (i < size))
                ++i;

        // loop through all samples
        while (i < size) {
                // measure from low to low
                while ((dest[i] > low) && (i < size))
                        ++i;
                startwave= i;
                while ((dest[i] < high) && (i < size))
                        ++i;
                while ((dest[i] > low) && (i < size))
                        ++i;
                //get minimum measured distance
                if (i-startwave < minClk && i < size)
                        minClk = i - startwave;
        }
        // set clock
        if (g_debugMode==2) prnt("DEBUG ASK: detectstrongASKclk smallest wave: %d",minClk);
        for (uint8_t clkCnt = 0; clkCnt<7; clkCnt++) {
                if (minClk >= fndClk[clkCnt]-(fndClk[clkCnt]/8) && minClk <= fndClk[clkCnt]+1)
                        return fndClk[clkCnt];
        }
        return 0;
}

// by marshmellow
// not perfect especially with lower clocks or VERY good antennas (heavy wave clipping)
// maybe somehow adjust peak trimming value based on samples to fix?
// return start index of best starting position for that clock and return clock (by reference)
int DetectASKClock(uint8_t dest[], size_t size, int *clock, int maxErr)
{
        size_t i=1;
        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+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)
                if (clk[i] == *clock) clockFnd = i;
                //clock found but continue to find best startpos

        //get high and low peak
        int peak, low;
        if (getHiLo(dest, loopCnt, &peak, &low, 75, 75) < 1) return -1;
        
        //test for large clean peaks
        if (!clockFnd){
                if (DetectCleanAskWave(dest, size, peak, low)==1){
                        int ans = DetectStrongAskClock(dest, size, peak, low);
                        if (g_debugMode==2) prnt("DEBUG ASK: detectaskclk Clean Ask Wave Detected: clk %d",ans);
                        for (i=clkEnd-1; i>0; i--){
                                if (clk[i] == ans) {
                                        *clock = ans;
                                        //clockFnd = i;
                                        return 0;  // for strong waves i don't use the 'best start position' yet...
                                        //break; //clock found but continue to find best startpos [not yet]
                                }
                        }
                }
        }
        uint8_t ii;
        uint8_t clkCnt, tol = 0;
        uint16_t bestErr[]={1000,1000,1000,1000,1000,1000,1000,1000,1000};
        uint8_t bestStart[]={0,0,0,0,0,0,0,0,0};
        size_t errCnt = 0;
        size_t arrLoc, loopEnd;

        if (clockFnd>0) {
                clkCnt = clockFnd;
                clkEnd = clockFnd+1;
        } else {
                clkCnt=1;
        }

        //test each valid clock from smallest to greatest to see which lines up
        for(; clkCnt < clkEnd; clkCnt++) {
                if (clk[clkCnt] <= 32) {
                        tol=1;
                } else {
                        tol=0;
                }
                //if no errors allowed - keep start within the first clock
                if (!maxErr && size > clk[clkCnt]*2 + tol && clk[clkCnt]<128) 
                        loopCnt = clk[clkCnt] * 2;

                bestErr[clkCnt] = 1000;

                //try lining up the peaks by moving starting point (try first few clocks)
                for (ii=0; ii < loopCnt; ii++){
                        if (dest[ii] < peak && dest[ii] > low) continue;

                        errCnt = 0;
                        // now that we have the first one lined up test rest of wave array
                        loopEnd = ((size-ii-tol) / clk[clkCnt]) - 1;
                        for (i=0; i < loopEnd; ++i){
                                arrLoc = ii + (i * clk[clkCnt]);
                                if (dest[arrLoc] >= peak || dest[arrLoc] <= low){
                                }else if (dest[arrLoc-tol] >= peak || dest[arrLoc-tol] <= low){
                                }else if (dest[arrLoc+tol] >= peak || dest[arrLoc+tol] <= low){
                                }else{  //error no peak detected
                                        errCnt++;
                                }
                        }
                        //if we found no errors then we can stop here and a low clock (common clocks)
                        //  this is correct one - return this clock
                        if (g_debugMode == 2) prnt("DEBUG ASK: clk %d, err %d, startpos %d, endpos %d", clk[clkCnt], errCnt, ii, i);
                        if (errCnt==0 && clkCnt<7) { 
                                if (!clockFnd) *clock = clk[clkCnt];
                                return ii;
                        }
                        //if we found errors see if it is lowest so far and save it as best run
                        if (errCnt < bestErr[clkCnt]) {
                                bestErr[clkCnt] = errCnt;
                                bestStart[clkCnt] = ii;
                        }
                }
        }
        uint8_t k;
        uint8_t best = 0;
        for (k=1; k < clkEnd; ++k){
                if (bestErr[k] < bestErr[best]){
                        if (bestErr[k] == 0) bestErr[k]=1;
                        // current best bit to error ratio     vs  new bit to error ratio
                        if ( (size/clk[best])/bestErr[best] < (size/clk[k])/bestErr[k] ){
                                best = k;
                        }
                }
                if (g_debugMode == 2) prnt("DEBUG ASK: clk %d, # Errors %d, Current Best Clk %d, bestStart %d", clk[k], bestErr[k], clk[best], bestStart[best]);
        }
        if (!clockFnd) *clock = clk[best];
        return bestStart[best];
}

//by marshmellow
//detect psk clock by reading each phase shift
// a phase shift is determined by measuring the sample length of each wave
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-20;

        //if we already have a valid clock quit
        size_t i=1;
        for (; i < 8; ++i)
                if (clk[i] == clock) return clock;

        size_t waveStart=0, waveEnd=0, firstFullWave=0, lastClkBit=0;
        uint8_t clkCnt, fc=0, fullWaveLen=0, tol=1;
        uint16_t peakcnt=0, errCnt=0, waveLenCnt=0;
        uint16_t bestErr[]={1000,1000,1000,1000,1000,1000,1000,1000,1000};
        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;
        if (g_debugMode==2) prnt("DEBUG PSK: FC: %d",fc);

        //find first full wave
        for (i=160; i<loopCnt; i++){
                if (dest[i] < dest[i+1] && dest[i+1] >= dest[i+2]){
                        if (waveStart == 0) {
                                waveStart = i+1;
                                //prnt("DEBUG: waveStart: %d",waveStart);
                        } else {
                                waveEnd = i+1;
                                //prnt("DEBUG: waveEnd: %d",waveEnd);
                                waveLenCnt = waveEnd-waveStart;
                                if (waveLenCnt > fc){
                                        firstFullWave = waveStart;
                                        fullWaveLen=waveLenCnt;
                                        break;
                                } 
                                waveStart=0;
                        }
                }
        }
        if (g_debugMode ==2) prnt("DEBUG PSK: 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--){
                lastClkBit = firstFullWave; //set end of wave as clock align
                waveStart = 0;
                errCnt=0;
                peakcnt=0;
                if (g_debugMode == 2) prnt("DEBUG PSK: clk: %d, lastClkBit: %d",clk[clkCnt],lastClkBit);

                for (i = firstFullWave+fullWaveLen-1; i < loopCnt-2; i++){
                        //top edge of wave = start of new wave 
                        if (dest[i] < dest[i+1] && dest[i+1] >= dest[i+2]){
                                if (waveStart == 0) {
                                        waveStart = i+1;
                                        waveLenCnt=0;
                                } else { //waveEnd
                                        waveEnd = i+1;
                                        waveLenCnt = waveEnd-waveStart;
                                        if (waveLenCnt > fc){ 
                                                //if this wave is a phase shift
                                                if (g_debugMode == 2) prnt("DEBUG PSK: phase shift at: %d, len: %d, nextClk: %d, i: %d, fc: %d",waveStart,waveLenCnt,lastClkBit+clk[clkCnt]-tol,i+1,fc);
                                                if (i+1 >= lastClkBit + clk[clkCnt] - tol){ //should be a clock bit
                                                        peakcnt++;
                                                        lastClkBit+=clk[clkCnt];
                                                } else if (i<lastClkBit+8){
                                                        //noise after a phase shift - ignore
                                                } else { //phase shift before supposed to based on clock
                                                        errCnt++;
                                                }
                                        } else if (i+1 > lastClkBit + clk[clkCnt] + tol + fc){
                                                lastClkBit+=clk[clkCnt]; //no phase shift but clock bit
                                        }
                                        waveStart=i+1;
                                }
                        }
                }
                if (errCnt == 0){
                        return clk[clkCnt];
                }
                if (errCnt <= bestErr[clkCnt]) bestErr[clkCnt]=errCnt;
                if (peakcnt > peaksdet[clkCnt]) peaksdet[clkCnt]=peakcnt;
        } 
        //all tested with errors 
        //return the highest clk with the most peaks found
        uint8_t best=7;
        for (i=7; i>=1; i--){
                if (peaksdet[i] > peaksdet[best]) {
                        best = i;
                }
                if (g_debugMode == 2) prnt("DEBUG PSK: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[i],peaksdet[i],bestErr[i],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;
        bool lastWasHigh = false;

        //find first valid beginning of a high or low wave
        while ((dest[i] >= peak || dest[i] <= low) && (i < size))
                ++i;
        while ((dest[i] < peak && dest[i] > low) && (i < size))
                ++i;
        lastWasHigh = (dest[i] >= peak);

        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;
        if (g_debugMode==2) prnt("DEBUG NRZ: detectstrongNRZclk smallest wave: %d",lowestTransition);
        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)
{
        size_t i=0;
        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-20;
        //if we already have a valid clock quit
        for (; i < 8; ++i)
                if (clk[i] == clock) return clock;

        //get high and low peak
        int peak, low;
        if (getHiLo(dest, loopCnt, &peak, &low, 75, 75) < 1) return 0;

        int lowestTransition = DetectStrongNRZClk(dest, size-20, peak, low);
        size_t ii;
        uint8_t clkCnt;
        uint8_t tol = 0;
        uint16_t smplCnt = 0;
        int16_t peakcnt = 0;
        int16_t peaksdet[] = {0,0,0,0,0,0,0,0};
        uint16_t maxPeak = 255;
        bool firstpeak = false;
        //test for large clipped waves
        for (i=0; i<loopCnt; i++){
                if (dest[i] >= peak || dest[i] <= low){
                        if (!firstpeak) continue;
                        smplCnt++;
                } else {
                        firstpeak=true;
                        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;
                        }
                }
        }
        bool errBitHigh = 0;
        bool bitHigh = 0;
        uint8_t ignoreCnt = 0;
        uint8_t ignoreWindow = 4;
        bool lastPeakHigh = 0;
        int lastBit = 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 smallest peak
                if (clk[clkCnt] < maxPeak - (clk[clkCnt]/4)) continue;
                //try lining up the peaks by moving starting point (try first 256)
                for (ii=20; ii < loopCnt; ++ii){
                        if ((dest[ii] >= peak) || (dest[ii] <= low)){
                                peakcnt=0;
                                bitHigh = false;
                                ignoreCnt = 0;
                                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 same peak don't count it
                                                        if ((dest[i] >= peak && !lastPeakHigh) || (dest[i] <= low && lastPeakHigh)) {
                                                peakcnt++;
                                                        }
                                                        lastPeakHigh = (dest[i] >= peak);
                                                        bitHigh = true;
                                                        errBitHigh = false;
                                                        ignoreCnt = ignoreWindow;
                                                        lastBit += clk[clkCnt];
                                                } else if (i == lastBit + clk[clkCnt] + tol) {
                                                        lastBit += clk[clkCnt];
                                                }
                                        //else if not a clock bit and no peaks
                                        } else if (dest[i] < peak && dest[i] > low){
                                                if (ignoreCnt==0){
                                                        bitHigh=false;
                                                        if (errBitHigh==true) peakcnt--;
                                                        errBitHigh=false;
                                                } else {
                                                        ignoreCnt--;
                                                }
                                                // else if not a clock bit but we have a peak
                                        } else if ((dest[i]>=peak || dest[i]<=low) && (!bitHigh)) {
                                                //error bar found no clock...
                                                errBitHigh=true;
                                        }
                                }
                                if(peakcnt>peaksdet[clkCnt]) {
                                        peaksdet[clkCnt]=peakcnt;
                                }
                        }
                }
        }
        int iii=7;
        uint8_t best=0;
        for (iii=7; iii > 0; iii--){
                if ((peaksdet[iii] >= (peaksdet[best]-1)) && (peaksdet[iii] <= peaksdet[best]+1) && lowestTransition) {
                        if (clk[iii] > (lowestTransition - (clk[iii]/8)) && clk[iii] < (lowestTransition + (clk[iii]/8))) {
                        best = iii;
                }
                } else if (peaksdet[iii] > peaksdet[best]){
                        best = iii;
                }
                if (g_debugMode==2) prnt("DEBUG NRZ: Clk: %d, peaks: %d, maxPeak: %d, bestClk: %d, lowestTrs: %d",clk[iii],peaksdet[iii],maxPeak, clk[best], lowestTransition);
        }

        return clk[best];
}

// by marshmellow
// convert psk1 demod to psk2 demod
// only transition waves are 1s
void psk1TOpsk2(uint8_t *BitStream, size_t size)
{
        size_t i=1;
        uint8_t lastBit=BitStream[0];
        for (; i<size; i++){
                if (BitStream[i]==7){
                        //ignore errors
                } else if (lastBit!=BitStream[i]){
                        lastBit=BitStream[i];
                        BitStream[i]=1;
                } else {
                        BitStream[i]=0;
                }
        }
        return;
}

// by marshmellow
// convert psk2 demod to psk1 demod
// from only transition waves are 1s to phase shifts change bit
void psk2TOpsk1(uint8_t *BitStream, size_t size)
{
        uint8_t phase=0;
        for (size_t i=0; i<size; i++){
                if (BitStream[i]==1){
                        phase ^=1;
                }
                BitStream[i]=phase;
        }
        return;
}

// redesigned by marshmellow adjusted from existing decode functions
// indala id decoding - only tested on 26 bit tags, but attempted to make it work for more
int indala26decode(uint8_t *bitStream, size_t *size, uint8_t *invert)
{
        //26 bit 40134 format  (don't know other formats)
        uint8_t preamble[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1};
        uint8_t preamble_i[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0};
        size_t startidx = 0; 
        if (!preambleSearch(bitStream, preamble, sizeof(preamble), size, &startidx)){
                // if didn't find preamble try again inverting
                if (!preambleSearch(bitStream, preamble_i, sizeof(preamble_i), size, &startidx)) return -1;
                *invert ^= 1;
        } 
        if (*size != 64 && *size != 224) return -2;
        if (*invert==1)
                for (size_t i = startidx; i < *size; i++)
                        bitStream[i] ^= 1;

        return (int) startidx;
}

// 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;
        *clk = DetectNRZClock(dest, *size, *clk);
        if (*clk==0) return -2;
        size_t i, gLen = 4096;
        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

        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;
        }
        //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;
                }
        }
        *size = numBits;
        return 0;
}

//by marshmellow
//detects the bit clock for FSK given the high and low Field Clocks
uint8_t detectFSKClk(uint8_t *BitStream, size_t size, uint8_t fcHigh, uint8_t fcLow)
{
        uint8_t clk[] = {8,16,32,40,50,64,100,128,0};
        uint16_t rfLens[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
        uint8_t rfCnts[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
        uint8_t rfLensFnd = 0;
        uint8_t lastFCcnt = 0;
        uint16_t fcCounter = 0;
        uint16_t rfCounter = 0;
        uint8_t firstBitFnd = 0;
        size_t i;
        if (size == 0) return 0;

        uint8_t fcTol = ((fcHigh*100 - fcLow*100)/2 + 50)/100; //(uint8_t)(0.5+(float)(fcHigh-fcLow)/2);
        rfLensFnd=0;
        fcCounter=0;
        rfCounter=0;
        firstBitFnd=0;
        //prnt("DEBUG: fcTol: %d",fcTol);
        // prime i to first peak / up transition
        for (i = 160; i < size-20; i++)
                if (BitStream[i] > BitStream[i-1] && BitStream[i]>=BitStream[i+1])
                        break;

        for (; i < size-20; i++){
                fcCounter++;
                rfCounter++;

                if (BitStream[i] <= BitStream[i-1] || BitStream[i] < BitStream[i+1]) 
                        continue;               
                // else new peak 
                // if we got less than the small fc + tolerance then set it to the small fc
                if (fcCounter < fcLow+fcTol) 
                        fcCounter = fcLow;
                else //set it to the large fc
                        fcCounter = fcHigh;

                //look for bit clock  (rf/xx)
                if ((fcCounter < lastFCcnt || fcCounter > lastFCcnt)){
                        //not the same size as the last wave - start of new bit sequence
                        if (firstBitFnd > 1){ //skip first wave change - probably not a complete bit
                                for (int ii=0; ii<15; ii++){
                                        if (rfLens[ii] >= (rfCounter-4) && rfLens[ii] <= (rfCounter+4)){
                                                rfCnts[ii]++;
                                                rfCounter = 0;
                                                break;
                                        }
                                }
                                if (rfCounter > 0 && rfLensFnd < 15){
                                        //prnt("DEBUG: rfCntr %d, fcCntr %d",rfCounter,fcCounter);
                                        rfCnts[rfLensFnd]++;
                                        rfLens[rfLensFnd++] = rfCounter;
                                }
                        } else {
                                firstBitFnd++;
                        }
                        rfCounter=0;
                        lastFCcnt=fcCounter;
                }
                fcCounter=0;
        }
        uint8_t rfHighest=15, rfHighest2=15, rfHighest3=15;

        for (i=0; i<15; i++){
                //get highest 2 RF values  (might need to get more values to compare or compare all?)
                if (rfCnts[i]>rfCnts[rfHighest]){
                        rfHighest3=rfHighest2;
                        rfHighest2=rfHighest;
                        rfHighest=i;
                } else if(rfCnts[i]>rfCnts[rfHighest2]){
                        rfHighest3=rfHighest2;
                        rfHighest2=i;
                } else if(rfCnts[i]>rfCnts[rfHighest3]){
                        rfHighest3=i;
                }
                if (g_debugMode==2) prnt("DEBUG FSK: RF %d, cnts %d",rfLens[i], rfCnts[i]);
        }  
        // set allowed clock remainder tolerance to be 1 large field clock length+1 
        //   we could have mistakenly made a 9 a 10 instead of an 8 or visa versa so rfLens could be 1 FC off  
        uint8_t tol1 = fcHigh+1; 
        
        if (g_debugMode==2) prnt("DEBUG FSK: most counted rf values: 1 %d, 2 %d, 3 %d",rfLens[rfHighest],rfLens[rfHighest2],rfLens[rfHighest3]);

        // loop to find the highest clock that has a remainder less than the tolerance
        //   compare samples counted divided by
        // test 128 down to 32 (shouldn't be possible to have fc/10 & fc/8 and rf/16 or less)
        int ii=7;
        for (; ii>=2; ii--){
                if (rfLens[rfHighest] % clk[ii] < tol1 || rfLens[rfHighest] % clk[ii] > clk[ii]-tol1){
                        if (rfLens[rfHighest2] % clk[ii] < tol1 || rfLens[rfHighest2] % clk[ii] > clk[ii]-tol1){
                                if (rfLens[rfHighest3] % clk[ii] < tol1 || rfLens[rfHighest3] % clk[ii] > clk[ii]-tol1){
                                        if (g_debugMode==2) prnt("DEBUG FSK: clk %d divides into the 3 most rf values within tolerance",clk[ii]);
                                        break;
                                }
                        }
                }
        }

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

        return clk[ii];
}

//by marshmellow
//countFC is to detect the field clock lengths.
//counts and returns the 2 most common wave lengths
//mainly used for FSK field clock detection
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 lastFCcnt=0;
        uint8_t fcCounter = 0;
        size_t i;
        if (size == 0) return 0;

        // prime i to first up transition
        for (i = 160; i < size-20; i++)
                if (BitStream[i] > BitStream[i-1] && BitStream[i] >= BitStream[i+1])
                        break;

        for (; i < size-20; i++){
                if (BitStream[i] > BitStream[i-1] && BitStream[i] >= BitStream[i+1]){
                        // new up transition
                        fcCounter++;
                        if (fskAdj){
                                //if we had 5 and now have 9 then go back to 8 (for when we get a fc 9 instead of an 8)
                                if (lastFCcnt==5 && fcCounter==9) fcCounter--;
                                //if fc=9 or 4 add one (for when we get a fc 9 instead of 10 or a 4 instead of a 5)
                                if ((fcCounter==9) || fcCounter==4) fcCounter++;
                        // save last field clock count  (fc/xx)
                        lastFCcnt = fcCounter;
                        }
                        // find which fcLens to save it to:
                        for (int ii=0; ii<15; ii++){
                                if (fcLens[ii]==fcCounter){
                                        fcCnts[ii]++;
                                        fcCounter=0;
                                        break;
                                }
                        }
                        if (fcCounter>0 && fcLensFnd<15){
                                //add new fc length 
                                fcCnts[fcLensFnd]++;
                                fcLens[fcLensFnd++]=fcCounter;
                        }
                        fcCounter=0;
                } else {
                        // count sample
                        fcCounter++;
                }
        }
        
        uint8_t best1=14, best2=14, best3=14;
        uint16_t maxCnt1=0;
        // go through fclens and find which ones are bigest 2  
        for (i=0; i<15; i++){
                // get the 3 best FC values
                if (fcCnts[i]>maxCnt1) {
                        best3=best2;
                        best2=best1;
                        maxCnt1=fcCnts[i];
                        best1=i;
                } else if(fcCnts[i]>fcCnts[best2]){
                        best3=best2;
                        best2=i;
                } else if(fcCnts[i]>fcCnts[best3]){
                        best3=i;
                }
                if (g_debugMode==2) prnt("DEBUG countfc: FC %u, Cnt %u, best fc: %u, best2 fc: %u",fcLens[i],fcCnts[i],fcLens[best1],fcLens[best2]);
        }
        if (fcLens[best1]==0) return 0;
        uint8_t fcH=0, fcL=0;
        if (fcLens[best1]>fcLens[best2]){
                fcH=fcLens[best1];
                fcL=fcLens[best2];
        } else{
                fcH=fcLens[best2];
                fcL=fcLens[best1];
        }
        if ((size-180)/fcH/3 > fcCnts[best1]+fcCnts[best2]) {
                if (g_debugMode==2) prnt("DEBUG countfc: fc is too large: %u > %u. Not psk or fsk",(size-180)/fcH/3,fcCnts[best1]+fcCnts[best2]);
                return 0; //lots of waves not psk or fsk
        }
        // TODO: take top 3 answers and compare to known Field clocks to get top 2

        uint16_t fcs = (((uint16_t)fcH)<<8) | fcL;
        if (fskAdj) return fcs; 
        return fcLens[best1];
}

//by marshmellow - demodulate PSK1 wave 
//uses wave lengths (# Samples) 
int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
{
        if (size == 0) return -1;
        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;
        uint16_t errCnt=0, waveLenCnt=0;
        fc = countFC(dest, *size, 0);
        if (fc!=2 && fc!=4 && fc!=8) return -1;
        //prnt("DEBUG: FC: %d",fc);
        *clock = DetectPSKClock(dest, *size, *clock);
        if (*clock == 0) return -1;
        int avgWaveVal=0, lastAvgWaveVal=0;
        //find first phase shift
        for (i=0; i<loopCnt; i++){
                if (dest[i]+fc < dest[i+1] && dest[i+1] >= dest[i+2]){
                        waveEnd = i+1;
                        //prnt("DEBUG: waveEnd: %d",waveEnd);
                        waveLenCnt = waveEnd-waveStart;
                        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;
                                //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
                                break;
                        } 
                        waveStart = i+1;
                        avgWaveVal = 0;
                }
                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;
        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++){
                //top edge of wave = start of new wave 
                if (dest[i]+fc < dest[i+1] && dest[i+1] >= dest[i+2]){
                        if (waveStart == 0) {
                                waveStart = i+1;
                                waveLenCnt = 0;
                                avgWaveVal = dest[i+1];
                        } else { //waveEnd
                                waveEnd = i+1;
                                waveLenCnt = waveEnd-waveStart;
                                lastAvgWaveVal = avgWaveVal/waveLenCnt;
                                if (waveLenCnt > fc){  
                                        //prnt("DEBUG: avgWaveVal: %d, waveSum: %d",lastAvgWaveVal,avgWaveVal);
                                        //this wave is a phase shift
                                        //prnt("DEBUG: phase shift at: %d, len: %d, nextClk: %d, i: %d, fc: %d",waveStart,waveLenCnt,lastClkBit+*clock-tol,i+1,fc);
                                        if (i+1 >= lastClkBit + *clock - tol){ //should be a clock bit
                                                curPhase ^= 1;
                                                dest[numBits++] = curPhase;
                                                lastClkBit += *clock;
                                        } else if (i < lastClkBit+10+fc){
                                                //noise after a phase shift - ignore
                                        } else { //phase shift before supposed to based on clock
                                                errCnt++;
                                                dest[numBits++] = 7;
                                        }
                                } else if (i+1 > lastClkBit + *clock + tol + fc){
                                        lastClkBit += *clock; //no phase shift but clock bit
                                        dest[numBits++] = curPhase;
                                }
                                avgWaveVal = 0;
                                waveStart = i+1;
                        }
                }
                avgWaveVal += dest[i+1];
        }
        *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 / 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;
        memset(tmpbuff, 0, sizeof(tmpbuff));
        memset(waveLen, 0, sizeof(waveLen));

        
        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/32)) {
                        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;
        } 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;
        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 && 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
                                                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 ( 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 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;
        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;
        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)
                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...
                if (g_debugMode==2) prnt("DEBUG STT: skipping STT at %d to %d", dataloc, dataloc+(clk*4));
                dataloc += clk*4;
        }
        *size = newloc;
        return true;
}