[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 <string.h>
#include "lfdemod.h"
uint8_t justNoise(uint8_t *BitStream, size_t size)
{
        static const uint8_t THRESHOLD = 123;
        //test samples are not just noise
        uint8_t justNoise1 = 1;
        for(size_t idx=0; idx < size && justNoise1 ;idx++){
                justNoise1 = BitStream[idx] < THRESHOLD;
        }
        return justNoise1;
}

//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);
        }
        //PrintAndLog("DEBUG: ans: %d, ptype: %d",ans,pType);
        return (ans == pType);
}

//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)
{
        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
uint8_t 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 0;  //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 || *size < 64) return 0;
        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 0;
                //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++;
                                                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)
{
        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;
        }
        return;
}

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

        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)) {
                errCnt = cleanAskRawDemod(BinStream, size, *clk, *invert, high, low);
                if (askType) //askman
                        return manrawdecode(BinStream, size, 0);        
                else //askraw
                        return errCnt;
        }

        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 = 1024;
        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) {
                                        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, ii;
        uint16_t bestErr = 1000, bestRun = 0;
        if (*size < 16) return -1;
        //find correct start position [alignment]
        for (ii=0;ii<2;++ii){
                for (i=ii; i<*size-3; i+=2)
                        if (BitStream[i]==BitStream[i+1])
                                errCnt++;

                if (bestErr>errCnt){
                        bestErr=errCnt;
                        bestRun=ii;
                }
                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;
}

//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;
}

//translate wave to 11111100000 (1 for each short wave 0 for each long wave)
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; 

        // sync to first lo-hi transition, and threshold

        // Need to threshold first sample

        if(dest[0] < 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 with anywhere
        // between 7 to 11 cycles so fuzz it by treat anything <9 as 8 and anything else as 10
        for(idx = 1; idx < size; 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]) { // 0 -> 1 transition
                        if ((idx-last_transition)<(fclow-2)){            //0-5 = garbage noise
                                //do nothing with extra garbage
                        } else if ((idx-last_transition) < (fchigh-1)) { //6-8 = 8 waves
                                dest[numBits++]=1;
                        } else if ((idx-last_transition) > (fchigh+1) && !numBits) { //12 + and first bit = garbage 
                                //do nothing with beginning garbage
                        } else {                                         //9+ = 10 waves
                                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
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; 
                
                //if lastval was 1, we have a 1->0 crossing
                if (dest[idx-1]==1) {
                        if (!numBits && n < rfLen/fclow) {
                                n=0;
                                lastval = dest[idx];
                                continue;
                        }
                        n = (n * fclow + rfLen/2) / rfLen;
                } else {// 0->1 crossing 
                        //test first bitsample too small
                        if (!numBits && n < rfLen/fchigh) {
                                n=0;
                                lastval = dest[idx];
                                continue;
                        }
                        n = (n * fchigh + rfLen/2) / rfLen; 
                }
                if (n == 0) n = 1;

                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
                if (dest[idx] && !dest[idx+1])  // 1 0
                        *lo=(*lo<<1)|1;
                else // 0 1
                        *lo=(*lo<<1)|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;
}

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);
                src++;
        }
        return num;
}

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
// takes a array of binary values, start position, length of bits per parity (includes parity bit),
//   Parity Type (1 for odd 0 for even), 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--;
                // if parity fails then return 0
                if (parityTest(parityWd, pLen, pType) == 0) return -1;
                bitCnt+=(pLen-1);
                parityWd = 0;
        }
        // if we got here then all the parities passed
        //return ID start index and size
        return bitCnt;
}

// Ask/Biphase Demod then try to locate an ISO 11784/85 ID
// BitStream must contain previously askrawdemod and biphasedemoded data
int ISO11784demodBI(uint8_t *dest, size_t *size)
{
        //make sure buffer has enough data
        if (*size < 128) return -1;

        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
        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 an 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};
        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;
}

// by marshmellow
// to detect a wave that has heavily clipped (clean) samples
uint8_t DetectCleanAskWave(uint8_t dest[], size_t size, uint8_t high, uint8_t low)
{
        uint16_t allPeaks=1;
        uint16_t cntPeaks=0;
        size_t loopEnd = 512+60;
        if (loopEnd > size) loopEnd = size;
        for (size_t i=60; i<loopEnd; i++){
                if (dest[i]>low && dest[i]<high) 
                        allPeaks=0;
                else
                        cntPeaks++;
        }
        if (allPeaks == 0){
                if (cntPeaks > 300) return 1;
        }
        return allPeaks;
}

// 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 = 0;
        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
        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) return -1; //not enough samples

        //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);
                        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
                                        //PrintAndLog("DEBUG: clk %d, err %d, ii %d, i %d",clk[clkCnt],errCnt,ii,i);
                        if(errCnt==0 && clkCnt<7) { 
                                if (!clockFnd) *clock = clk[clkCnt];
                                return ii;
                        }
                        //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 iii;
        uint8_t best=0;
        for (iii=1; iii<clkEnd; ++iii){
                if (bestErr[iii] < bestErr[best]){
                        if (bestErr[iii] == 0) bestErr[iii]=1;
                        // current best bit to error ratio     vs  new bit to error ratio
                        if ( (size/clk[best])/bestErr[best] < (size/clk[iii])/bestErr[iii] ){
                                best = iii;
                        }
                }
        }
        //if (bestErr[best] > maxErr) return -1;
        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;

        //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;
        //PrintAndLog("DEBUG: FC: %d",fc);

        //find first full wave
        for (i=0; i<loopCnt; i++){
                if (dest[i] < dest[i+1] && dest[i+1] >= dest[i+2]){
                        if (waveStart == 0) {
                                waveStart = i+1;
                                //PrintAndLog("DEBUG: waveStart: %d",waveStart);
                        } else {
                                waveEnd = i+1;
                                //PrintAndLog("DEBUG: waveEnd: %d",waveEnd);
                                waveLenCnt = waveEnd-waveStart;
                                if (waveLenCnt > fc){
                                        firstFullWave = waveStart;
                                        fullWaveLen=waveLenCnt;
                                        break;
                                } 
                                waveStart=0;
                        }
                }
        }
        //PrintAndLog("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);
        
        //test each valid clock from greatest to smallest to see which lines up
        for(clkCnt=7; clkCnt >= 1 ; clkCnt--){
                lastClkBit = firstFullWave; //set end of wave as clock align
                waveStart = 0;
                errCnt=0;
                peakcnt=0;
                //PrintAndLog("DEBUG: clk: %d, lastClkBit: %d",clk[clkCnt],lastClkBit);

                for (i = firstFullWave+fullWaveLen-1; i < loopCnt-2; i++){
                        //top edge of wave = start of new wave 
                        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
                                                //PrintAndLog("DEBUG: phase shift at: %d, len: %d, nextClk: %d, ii: %d, fc: %d",waveStart,waveLenCnt,lastClkBit+clk[clkCnt]-tol,ii+1,fc);
                                                if (i+1 >= lastClkBit + clk[clkCnt] - tol){ //should be a clock bit
                                                        peakcnt++;
                                                        lastClkBit+=clk[clkCnt];
                                                } 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;
                }
                //PrintAndLog("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best]);
        }
        return clk[best];
}

//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;

        //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;

        //PrintAndLog("DEBUG: peak: %d, low: %d",peak,low);
        size_t ii;
        uint8_t clkCnt;
        uint8_t tol = 0;
        uint16_t peakcnt=0;
        uint16_t peaksdet[]={0,0,0,0,0,0,0,0};
        uint16_t maxPeak=0;
        //test for large clipped waves
        for (i=0; i<loopCnt; i++){
                if (dest[i] >= peak || dest[i] <= low){
                        peakcnt++;
                } else {
                        if (peakcnt>0 && maxPeak < peakcnt){
                                maxPeak = peakcnt;
                        }
                        peakcnt=0;
                }
        }
        peakcnt=0;
        //test each valid clock from smallest to greatest to see which lines up
        for(clkCnt=0; clkCnt < 8; ++clkCnt){
                //ignore clocks smaller than largest peak
                if (clk[clkCnt]<maxPeak) continue;

                //try lining up the peaks by moving starting point (try first 256)
                for (ii=0; ii< loopCnt; ++ii){
                        if ((dest[ii] >= peak) || (dest[ii] <= low)){
                                peakcnt=0;
                                // now that we have the first one lined up test rest of wave array
                                for (i=0; i < ((int)((size-ii-tol)/clk[clkCnt])-1); ++i){
                                        if (dest[ii+(i*clk[clkCnt])]>=peak || dest[ii+(i*clk[clkCnt])]<=low){
                                                peakcnt++;
                                        }
                                }
                                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]){
                        best = iii;
                }
                //PrintAndLog("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best]);
        }
        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)
        int i;
        int long_wait=29;//29 leading zeros in format
        int start;
        int first = 0;
        int first2 = 0;
        int bitCnt = 0;
        int ii;
        // Finding the start of a UID
        for (start = 0; start <= *size - 250; start++) {
                first = bitStream[start];
                for (i = start; i < start + long_wait; i++) {
                        if (bitStream[i] != first) {
                                break;
                        }
                }
                if (i == (start + long_wait)) {
                        break;
                }
        }
        if (start == *size - 250 + 1) {
                // did not find start sequence
                return -1;
        }
        // Inverting signal if needed
        if (first == 1) {
                for (i = start; i < *size; i++) {
                        bitStream[i] = !bitStream[i];
                }
                *invert = 1;
        }else *invert=0;

        int iii;
        //found start once now test length by finding next one
        for (ii=start+29; ii <= *size - 250; ii++) {
                first2 = bitStream[ii];
                for (iii = ii; iii < ii + long_wait; iii++) {
                        if (bitStream[iii] != first2) {
                                break;
                        }
                }
                if (iii == (ii + long_wait)) {
                        break;
                }
        }
        if (ii== *size - 250 + 1){
                // did not find second start sequence
                return -2;
        }
        bitCnt=ii-start;

        // Dumping UID
        i = start;
        for (ii = 0; ii < bitCnt; ii++) {
                bitStream[ii] = bitStream[i++];
        }
        *size=bitCnt;
        return 1;
}

// by marshmellow - demodulate NRZ wave (both similar enough)
// peaks invert bit (high=1 low=0) each clock cycle = 1 bit determined by last peak
// there probably is a much simpler way to do this.... 
int nrzRawDemod(uint8_t *dest, size_t *size, int *clk, int *invert, int maxErr)
{
        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;
        int high, low;
        if (getHiLo(dest, gLen, &high, &low, 75, 75) < 1) return -3; //25% fuzz on high 25% fuzz on low
        int lastBit = 0;  //set first clock check
        size_t iii = 0, bitnum = 0; //bitnum counter
        uint16_t errCnt = 0, MaxBits = 1000;
        size_t bestErrCnt = maxErr+1;
        size_t bestPeakCnt = 0, bestPeakStart = 0;
        uint8_t bestFirstPeakHigh=0, firstPeakHigh=0, curBit=0, bitHigh=0, errBitHigh=0;
        uint8_t tol = 1;  //clock tolerance adjust - waves will be accepted as within the clock if they fall + or - this value + clock from last valid wave
        uint16_t peakCnt=0;
        uint8_t ignoreWindow=4;
        uint8_t ignoreCnt=ignoreWindow; //in case of noise near peak
        //loop to find first wave that works - align to clock
        for (iii=0; iii < gLen; ++iii){
                if ((dest[iii]>=high) || (dest[iii]<=low)){
                        if (dest[iii]>=high) firstPeakHigh=1;
                        else firstPeakHigh=0;
                        lastBit=iii-*clk;
                        peakCnt=0;
                        errCnt=0;
                        //loop through to see if this start location works
                        for (i = iii; i < *size; ++i) {
                                // if we are at a clock bit
                                if ((i >= lastBit + *clk - tol) && (i <= lastBit + *clk + tol)) {
                                        //test high/low
                                        if (dest[i] >= high || dest[i] <= low) {
                                                bitHigh = 1;
                                                peakCnt++;
                                                errBitHigh = 0;
                                                ignoreCnt = ignoreWindow;
                                                lastBit += *clk;
                                        } else if (i == lastBit + *clk + tol) {
                                                lastBit += *clk;
                                        }
                                //else if no bars found
                                } else if (dest[i] < high && dest[i] > low){
                                        if (ignoreCnt==0){
                                                bitHigh=0;
                                                if (errBitHigh==1) errCnt++;
                                                errBitHigh=0;
                                        } else {
                                                ignoreCnt--;
                                        }
                                } else if ((dest[i]>=high || dest[i]<=low) && (bitHigh==0)) {
                                        //error bar found no clock...
                                        errBitHigh=1;
                                }
                                if (((i-iii) / *clk)>=MaxBits) break;
                        }
                        //we got more than 64 good bits and not all errors
                        if (((i-iii) / *clk) > 64 && (errCnt <= (maxErr))) {
                                //possible good read
                                if (!errCnt || peakCnt > bestPeakCnt){
                                        bestFirstPeakHigh=firstPeakHigh;
                                        bestErrCnt = errCnt;
                                        bestPeakCnt = peakCnt;
                                        bestPeakStart = iii;
                                        if (!errCnt) break;  //great read - finish
                                }
                        }
                }
        }
        //PrintAndLog("DEBUG: bestErrCnt: %d, maxErr: %d, bestStart: %d, bestPeakCnt: %d, bestPeakStart: %d",bestErrCnt,maxErr,bestStart,bestPeakCnt,bestPeakStart);
        if (bestErrCnt > maxErr) return bestErrCnt;             

        //best run is good enough set to best run and set overwrite BinStream
        lastBit = bestPeakStart - *clk;
        memset(dest, bestFirstPeakHigh^1, bestPeakStart / *clk);
        bitnum += (bestPeakStart / *clk);
        for (i = bestPeakStart; i < *size; ++i) {
                // if expecting a clock bit
                if ((i >= lastBit + *clk - tol) && (i <= lastBit + *clk + tol)) {
                        // test high/low
                        if (dest[i] >= high || dest[i] <= low) {
                                peakCnt++;
                                bitHigh = 1;
                                errBitHigh = 0;
                                ignoreCnt = ignoreWindow;
                                curBit = *invert;
                                if (dest[i] >= high) curBit ^= 1;
                                dest[bitnum++] = curBit;
                                lastBit += *clk;
                        //else no bars found in clock area
                        } else if (i == lastBit + *clk + tol) {
                                dest[bitnum++] = curBit;
                                lastBit += *clk;
                        }
                //else if no bars found
                } else if (dest[i] < high && dest[i] > low){
                        if (ignoreCnt == 0){
                                bitHigh = 0;
                                if (errBitHigh == 1){
                                        dest[bitnum++] = 7;
                                        errCnt++;
                                }
                                errBitHigh=0;
                        } else {
                                ignoreCnt--;
                        }
                } else if ((dest[i] >= high || dest[i] <= low) && (bitHigh == 0)) {
                        //error bar found no clock...
                        errBitHigh=1;
                }
                if (bitnum >= MaxBits) break;
        }
        *size = bitnum;
        return bestErrCnt;
}

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

        for (; i < size-1; 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){
                                                rfCnts[ii]++;
                                                rfCounter = 0;
                                                break;
                                        }
                                }
                                if (rfCounter > 0 && rfLensFnd < 15){
                                        //PrintAndLog("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++){
                //PrintAndLog("DEBUG: RF %d, cnts %d",rfLens[i], rfCnts[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;
                }
        }  
        // 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; 
        
        //PrintAndLog("DEBUG: hightest: 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
        int ii=7;
        for (; ii>=0; 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){
                                        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};
        uint16_t fcCnts[] = {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 = 1; i < size-1; i++)
                if (BitStream[i] > BitStream[i-1] && BitStream[i] >= BitStream[i+1])
                        break;

        for (; i < size-1; 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<10; ii++){
                                if (fcLens[ii]==fcCounter){
                                        fcCnts[ii]++;
                                        fcCounter=0;
                                        break;
                                }
                        }
                        if (fcCounter>0 && fcLensFnd<10){
                                //add new fc length 
                                fcCnts[fcLensFnd]++;
                                fcLens[fcLensFnd++]=fcCounter;
                        }
                        fcCounter=0;
                } else {
                        // count sample
                        fcCounter++;
                }
        }
        
        uint8_t best1=9, best2=9, best3=9;
        uint16_t maxCnt1=0;
        // go through fclens and find which ones are bigest 2  
        for (i=0; i<10; i++){
                // PrintAndLog("DEBUG: FC %d, Cnt %d, Errs %d",fcLens[i],fcCnts[i],errCnt);    
                // 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;
                }
        }
        uint8_t fcH=0, fcL=0;
        if (fcLens[best1]>fcLens[best2]){
                fcH=fcLens[best1];
                fcL=fcLens[best2];
        } else{
                fcH=fcLens[best2];
                fcL=fcLens[best1];
        }

        // TODO: take top 3 answers and compare to known Field clocks to get top 2

        uint16_t fcs = (((uint16_t)fcH)<<8) | fcL;
        // PrintAndLog("DEBUG: Best %d  best2 %d best3 %d",fcLens[best1],fcLens[best2],fcLens[best3]);
        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;

        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;
        //PrintAndLog("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;
                        //PrintAndLog("DEBUG: waveEnd: %d",waveEnd);
                        waveLenCnt = waveEnd-waveStart;
                        if (waveLenCnt > fc && waveStart > fc){ //not first peak and is a large wave 
                                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];
        }
        //PrintAndLog("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);  
        lastClkBit = firstFullWave; //set start of wave as clock align
        //PrintAndLog("DEBUG: clk: %d, lastClkBit: %d", *clock, lastClkBit);
        waveStart = 0;
        size_t numBits=0;
        //set skipped bits
        memset(dest, curPhase^1, firstFullWave / *clock);
        numBits += (firstFullWave / *clock);
        dest[numBits++] = curPhase; //set first read bit
        for (i = firstFullWave + fullWaveLen - 1; i < *size-3; i++){
                //top edge of wave = start of new wave 
                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){  
                                        //PrintAndLog("DEBUG: avgWaveVal: %d, waveSum: %d",lastAvgWaveVal,avgWaveVal);
                                        //this wave is a phase shift
                                        //PrintAndLog("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;
}