fixed CMD_HID_SIM_TAG

[proxmark3-svn] / armsrc / lfops.c

//-----------------------------------------------------------------------------
// 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.
//-----------------------------------------------------------------------------
// Miscellaneous routines for low frequency tag operations.
// Tags supported here so far are Texas Instruments (TI), HID
// Also routines for raw mode reading/simulating of LF waveform
//-----------------------------------------------------------------------------

#include "proxmark3.h"
#include "apps.h"
#include "util.h"
#include "hitag2.h"
#include "crc16.h"
#include "string.h"

void AcquireRawAdcSamples125k(int at134khz)
{
        if (at134khz)
                FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 88); //134.8Khz
        else
                FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz

        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);

        // Connect the A/D to the peak-detected low-frequency path.
        SetAdcMuxFor(GPIO_MUXSEL_LOPKD);

        // Give it a bit of time for the resonant antenna to settle.
        SpinDelay(50);

        // Now set up the SSC to get the ADC samples that are now streaming at us.
        FpgaSetupSsc();

        // Now call the acquisition routine
        DoAcquisition125k();
}

// split into two routines so we can avoid timing issues after sending commands //
void DoAcquisition125k(void)
{
        uint8_t *dest = (uint8_t *)BigBuf;
        int n = sizeof(BigBuf);
        int i;

        memset(dest, 0, n);
        i = 0;
        for(;;) {
                if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
                        AT91C_BASE_SSC->SSC_THR = 0x43;
                        LED_D_ON();
                }
                if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY) {
                        dest[i] = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        i++;
                        LED_D_OFF();
                        if (i >= n) break;
                }
        }
        Dbprintf("buffer samples: %02x %02x %02x %02x %02x %02x %02x %02x ...",
                        dest[0], dest[1], dest[2], dest[3], dest[4], dest[5], dest[6], dest[7]);
}

void ModThenAcquireRawAdcSamples125k(int delay_off, int period_0, int period_1, uint8_t *command)
{
        int at134khz;

        /* Make sure the tag is reset */
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelay(2500);

        // see if 'h' was specified
        if (command[strlen((char *) command) - 1] == 'h')
                at134khz = TRUE;
        else
                at134khz = FALSE;

        if (at134khz)
                FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 88); //134.8Khz
        else
                FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz

        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);

        // Give it a bit of time for the resonant antenna to settle.
        SpinDelay(50);
        // And a little more time for the tag to fully power up
        SpinDelay(2000);

        // Now set up the SSC to get the ADC samples that are now streaming at us.
        FpgaSetupSsc();

        // now modulate the reader field
        while(*command != '\0' && *command != ' ') {
                FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
                LED_D_OFF();
                SpinDelayUs(delay_off);
                if (at134khz)
                        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 88); //134.8Khz
                else
                        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz

                FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
                LED_D_ON();
                if(*(command++) == '0')
                        SpinDelayUs(period_0);
                else
                        SpinDelayUs(period_1);
        }
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        LED_D_OFF();
        SpinDelayUs(delay_off);
        if (at134khz)
                FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 88); //134.8Khz
        else
                FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz

        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);

        // now do the read
        DoAcquisition125k();
}

/* blank r/w tag data stream
...0000000000000000 01111111
1010101010101010101010101010101010101010101010101010101010101010
0011010010100001
01111111
101010101010101[0]000...

[5555fe852c5555555555555555fe0000]
*/
void ReadTItag(void)
{
        // some hardcoded initial params
        // when we read a TI tag we sample the zerocross line at 2Mhz
        // TI tags modulate a 1 as 16 cycles of 123.2Khz
        // TI tags modulate a 0 as 16 cycles of 134.2Khz
        #define FSAMPLE 2000000
        #define FREQLO 123200
        #define FREQHI 134200

        signed char *dest = (signed char *)BigBuf;
        int n = sizeof(BigBuf);
//      int *dest = GraphBuffer;
//      int n = GraphTraceLen;

        // 128 bit shift register [shift3:shift2:shift1:shift0]
        uint32_t shift3 = 0, shift2 = 0, shift1 = 0, shift0 = 0;

        int i, cycles=0, samples=0;
        // how many sample points fit in 16 cycles of each frequency
        uint32_t sampleslo = (FSAMPLE<<4)/FREQLO, sampleshi = (FSAMPLE<<4)/FREQHI;
        // when to tell if we're close enough to one freq or another
        uint32_t threshold = (sampleslo - sampleshi + 1)>>1;

        // TI tags charge at 134.2Khz
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 88); //134.8Khz

        // Place FPGA in passthrough mode, in this mode the CROSS_LO line
        // connects to SSP_DIN and the SSP_DOUT logic level controls
        // whether we're modulating the antenna (high)
        // or listening to the antenna (low)
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_PASSTHRU);

        // get TI tag data into the buffer
        AcquireTiType();

        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);

        for (i=0; i<n-1; i++) {
                // count cycles by looking for lo to hi zero crossings
                if ( (dest[i]<0) && (dest[i+1]>0) ) {
                        cycles++;
                        // after 16 cycles, measure the frequency
                        if (cycles>15) {
                                cycles=0;
                                samples=i-samples; // number of samples in these 16 cycles

                                // TI bits are coming to us lsb first so shift them
                                // right through our 128 bit right shift register
                          shift0 = (shift0>>1) | (shift1 << 31);
                          shift1 = (shift1>>1) | (shift2 << 31);
                          shift2 = (shift2>>1) | (shift3 << 31);
                          shift3 >>= 1;

                                // check if the cycles fall close to the number
                                // expected for either the low or high frequency
                                if ( (samples>(sampleslo-threshold)) && (samples<(sampleslo+threshold)) ) {
                                        // low frequency represents a 1
                                        shift3 |= (1<<31);
                                } else if ( (samples>(sampleshi-threshold)) && (samples<(sampleshi+threshold)) ) {
                                        // high frequency represents a 0
                                } else {
                                        // probably detected a gay waveform or noise
                                        // use this as gaydar or discard shift register and start again
                                        shift3 = shift2 = shift1 = shift0 = 0;
                                }
                                samples = i;

                                // for each bit we receive, test if we've detected a valid tag

                                // if we see 17 zeroes followed by 6 ones, we might have a tag
                                // remember the bits are backwards
                                if ( ((shift0 & 0x7fffff) == 0x7e0000) ) {
                                        // if start and end bytes match, we have a tag so break out of the loop
                                        if ( ((shift0>>16)&0xff) == ((shift3>>8)&0xff) ) {
                                                cycles = 0xF0B; //use this as a flag (ugly but whatever)
                                                break;
                                        }
                                }
                        }
                }
        }

        // if flag is set we have a tag
        if (cycles!=0xF0B) {
                DbpString("Info: No valid tag detected.");
        } else {
          // put 64 bit data into shift1 and shift0
          shift0 = (shift0>>24) | (shift1 << 8);
          shift1 = (shift1>>24) | (shift2 << 8);

                // align 16 bit crc into lower half of shift2
          shift2 = ((shift2>>24) | (shift3 << 8)) & 0x0ffff;

                // if r/w tag, check ident match
                if ( shift3&(1<<15) ) {
                        DbpString("Info: TI tag is rewriteable");
                        // only 15 bits compare, last bit of ident is not valid
                        if ( ((shift3>>16)^shift0)&0x7fff ) {
                                DbpString("Error: Ident mismatch!");
                        } else {
                                DbpString("Info: TI tag ident is valid");
                        }
                } else {
                        DbpString("Info: TI tag is readonly");
                }

                // WARNING the order of the bytes in which we calc crc below needs checking
                // i'm 99% sure the crc algorithm is correct, but it may need to eat the
                // bytes in reverse or something
                // calculate CRC
                uint32_t crc=0;

                crc = update_crc16(crc, (shift0)&0xff);
                crc = update_crc16(crc, (shift0>>8)&0xff);
                crc = update_crc16(crc, (shift0>>16)&0xff);
                crc = update_crc16(crc, (shift0>>24)&0xff);
                crc = update_crc16(crc, (shift1)&0xff);
                crc = update_crc16(crc, (shift1>>8)&0xff);
                crc = update_crc16(crc, (shift1>>16)&0xff);
                crc = update_crc16(crc, (shift1>>24)&0xff);

                Dbprintf("Info: Tag data: %x%08x, crc=%x",
                        (unsigned int)shift1, (unsigned int)shift0, (unsigned int)shift2 & 0xFFFF);
                if (crc != (shift2&0xffff)) {
                        Dbprintf("Error: CRC mismatch, expected %x", (unsigned int)crc);
                } else {
                        DbpString("Info: CRC is good");
                }
        }
}

void WriteTIbyte(uint8_t b)
{
        int i = 0;

        // modulate 8 bits out to the antenna
        for (i=0; i<8; i++)
        {
                if (b&(1<<i)) {
                        // stop modulating antenna
                        LOW(GPIO_SSC_DOUT);
                        SpinDelayUs(1000);
                        // modulate antenna
                        HIGH(GPIO_SSC_DOUT);
                        SpinDelayUs(1000);
                } else {
                        // stop modulating antenna
                        LOW(GPIO_SSC_DOUT);
                        SpinDelayUs(300);
                        // modulate antenna
                        HIGH(GPIO_SSC_DOUT);
                        SpinDelayUs(1700);
                }
        }
}

void AcquireTiType(void)
{
        int i, j, n;
        // tag transmission is <20ms, sampling at 2M gives us 40K samples max
        // each sample is 1 bit stuffed into a uint32_t so we need 1250 uint32_t
        #define TIBUFLEN 1250

        // clear buffer
        memset(BigBuf,0,sizeof(BigBuf));

        // Set up the synchronous serial port
        AT91C_BASE_PIOA->PIO_PDR = GPIO_SSC_DIN;
        AT91C_BASE_PIOA->PIO_ASR = GPIO_SSC_DIN;

        // steal this pin from the SSP and use it to control the modulation
        AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
        AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;

        AT91C_BASE_SSC->SSC_CR = AT91C_SSC_SWRST;
        AT91C_BASE_SSC->SSC_CR = AT91C_SSC_RXEN | AT91C_SSC_TXEN;

        // Sample at 2 Mbit/s, so TI tags are 16.2 vs. 14.9 clocks long
        // 48/2 = 24 MHz clock must be divided by 12
        AT91C_BASE_SSC->SSC_CMR = 12;

        AT91C_BASE_SSC->SSC_RCMR = SSC_CLOCK_MODE_SELECT(0);
        AT91C_BASE_SSC->SSC_RFMR = SSC_FRAME_MODE_BITS_IN_WORD(32) | AT91C_SSC_MSBF;
        AT91C_BASE_SSC->SSC_TCMR = 0;
        AT91C_BASE_SSC->SSC_TFMR = 0;

        LED_D_ON();

        // modulate antenna
        HIGH(GPIO_SSC_DOUT);

        // Charge TI tag for 50ms.
        SpinDelay(50);

        // stop modulating antenna and listen
        LOW(GPIO_SSC_DOUT);

        LED_D_OFF();

        i = 0;
        for(;;) {
                if(AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY) {
                        BigBuf[i] = AT91C_BASE_SSC->SSC_RHR;    // store 32 bit values in buffer
                        i++; if(i >= TIBUFLEN) break;
                }
                WDT_HIT();
        }

        // return stolen pin to SSP
        AT91C_BASE_PIOA->PIO_PDR = GPIO_SSC_DOUT;
        AT91C_BASE_PIOA->PIO_ASR = GPIO_SSC_DIN | GPIO_SSC_DOUT;

        char *dest = (char *)BigBuf;
        n = TIBUFLEN*32;
        // unpack buffer
        for (i=TIBUFLEN-1; i>=0; i--) {
                for (j=0; j<32; j++) {
                        if(BigBuf[i] & (1 << j)) {
                                dest[--n] = 1;
                        } else {
                                dest[--n] = -1;
                        }
                }
        }
}

// arguments: 64bit data split into 32bit idhi:idlo and optional 16bit crc
// if crc provided, it will be written with the data verbatim (even if bogus)
// if not provided a valid crc will be computed from the data and written.
void WriteTItag(uint32_t idhi, uint32_t idlo, uint16_t crc)
{
        if(crc == 0) {
                crc = update_crc16(crc, (idlo)&0xff);
                crc = update_crc16(crc, (idlo>>8)&0xff);
                crc = update_crc16(crc, (idlo>>16)&0xff);
                crc = update_crc16(crc, (idlo>>24)&0xff);
                crc = update_crc16(crc, (idhi)&0xff);
                crc = update_crc16(crc, (idhi>>8)&0xff);
                crc = update_crc16(crc, (idhi>>16)&0xff);
                crc = update_crc16(crc, (idhi>>24)&0xff);
        }
        Dbprintf("Writing to tag: %x%08x, crc=%x",
                (unsigned int) idhi, (unsigned int) idlo, crc);

        // TI tags charge at 134.2Khz
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 88); //134.8Khz
        // Place FPGA in passthrough mode, in this mode the CROSS_LO line
        // connects to SSP_DIN and the SSP_DOUT logic level controls
        // whether we're modulating the antenna (high)
        // or listening to the antenna (low)
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_PASSTHRU);
        LED_A_ON();

        // steal this pin from the SSP and use it to control the modulation
        AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
        AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;

        // writing algorithm:
        // a high bit consists of a field off for 1ms and field on for 1ms
        // a low bit consists of a field off for 0.3ms and field on for 1.7ms
        // initiate a charge time of 50ms (field on) then immediately start writing bits
        // start by writing 0xBB (keyword) and 0xEB (password)
        // then write 80 bits of data (or 64 bit data + 16 bit crc if you prefer)
        // finally end with 0x0300 (write frame)
        // all data is sent lsb firts
        // finish with 15ms programming time

        // modulate antenna
        HIGH(GPIO_SSC_DOUT);
        SpinDelay(50);  // charge time

        WriteTIbyte(0xbb); // keyword
        WriteTIbyte(0xeb); // password
        WriteTIbyte( (idlo    )&0xff );
        WriteTIbyte( (idlo>>8 )&0xff );
        WriteTIbyte( (idlo>>16)&0xff );
        WriteTIbyte( (idlo>>24)&0xff );
        WriteTIbyte( (idhi    )&0xff );
        WriteTIbyte( (idhi>>8 )&0xff );
        WriteTIbyte( (idhi>>16)&0xff );
        WriteTIbyte( (idhi>>24)&0xff ); // data hi to lo
        WriteTIbyte( (crc     )&0xff ); // crc lo
        WriteTIbyte( (crc>>8  )&0xff ); // crc hi
        WriteTIbyte(0x00); // write frame lo
        WriteTIbyte(0x03); // write frame hi
        HIGH(GPIO_SSC_DOUT);
        SpinDelay(50);  // programming time

        LED_A_OFF();

        // get TI tag data into the buffer
        AcquireTiType();

        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        DbpString("Now use tiread to check");
}

void SimulateTagLowFrequency(int period, int gap, int ledcontrol)
{
        int i;
        uint8_t *tab = (uint8_t *)BigBuf;
    
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_EDGE_DETECT);
    
        AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT | GPIO_SSC_CLK;
    
        AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
        AT91C_BASE_PIOA->PIO_ODR = GPIO_SSC_CLK;
    
#define SHORT_COIL()    LOW(GPIO_SSC_DOUT)
#define OPEN_COIL()             HIGH(GPIO_SSC_DOUT)
    
        i = 0;
        for(;;) {
                while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)) {
                        if(BUTTON_PRESS()) {
                                DbpString("Stopped");
                                return;
                        }
                        WDT_HIT();
                }
        
                if (ledcontrol)
                        LED_D_ON();
        
                if(tab[i])
                        OPEN_COIL();
                else
                        SHORT_COIL();
        
                if (ledcontrol)
                        LED_D_OFF();
        
                while(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK) {
                        if(BUTTON_PRESS()) {
                                DbpString("Stopped");
                                return;
                        }
                        WDT_HIT();
                }
        
                i++;
                if(i == period) {
                        i = 0;
                        if (gap) {
                                SHORT_COIL();
                                SpinDelayUs(gap);
                        }
                }
        }
}

#define DEBUG_FRAME_CONTENTS 1
void SimulateTagLowFrequencyBidir(int divisor, int t0)
{
}

// compose fc/8 fc/10 waveform
static void fc(int c, int *n) {
        uint8_t *dest = (uint8_t *)BigBuf;
        int idx;

        // for when we want an fc8 pattern every 4 logical bits
        if(c==0) {
                dest[((*n)++)]=1;
                dest[((*n)++)]=1;
                dest[((*n)++)]=0;
                dest[((*n)++)]=0;
                dest[((*n)++)]=0;
                dest[((*n)++)]=0;
                dest[((*n)++)]=0;
                dest[((*n)++)]=0;
        }
        //      an fc/8  encoded bit is a bit pattern of  11000000  x6 = 48 samples
        if(c==8) {
                for (idx=0; idx<6; idx++) {
                        dest[((*n)++)]=1;
                        dest[((*n)++)]=1;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                }
        }

        //      an fc/10 encoded bit is a bit pattern of 1110000000 x5 = 50 samples
        if(c==10) {
                for (idx=0; idx<5; idx++) {
                        dest[((*n)++)]=1;
                        dest[((*n)++)]=1;
                        dest[((*n)++)]=1;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                        dest[((*n)++)]=0;
                }
        }
}

// prepare a waveform pattern in the buffer based on the ID given then
// simulate a HID tag until the button is pressed
void CmdHIDsimTAG(int hi, int lo, int ledcontrol)
{
        int n=0, i=0;
        /*
         HID tag bitstream format
         The tag contains a 44bit unique code. This is sent out MSB first in sets of 4 bits
         A 1 bit is represented as 6 fc8 and 5 fc10 patterns
         A 0 bit is represented as 5 fc10 and 6 fc8 patterns
         A fc8 is inserted before every 4 bits
         A special start of frame pattern is used consisting a0b0 where a and b are neither 0
         nor 1 bits, they are special patterns (a = set of 12 fc8 and b = set of 10 fc10)
        */

        if (hi>0xFFF) {
                DbpString("Tags can only have 44 bits.");
                return;
        }
        fc(0,&n);
        // special start of frame marker containing invalid bit sequences
        fc(8,  &n);     fc(8,  &n);     // invalid
        fc(8,  &n);     fc(10, &n); // logical 0
        fc(10, &n);     fc(10, &n); // invalid
        fc(8,  &n);     fc(10, &n); // logical 0

        WDT_HIT();
        // manchester encode bits 43 to 32
        for (i=11; i>=0; i--) {
                if ((i%4)==3) fc(0,&n);
                if ((hi>>i)&1) {
                        fc(10, &n);     fc(8,  &n);             // low-high transition
                } else {
                        fc(8,  &n);     fc(10, &n);             // high-low transition
                }
        }

        WDT_HIT();
        // manchester encode bits 31 to 0
        for (i=31; i>=0; i--) {
                if ((i%4)==3) fc(0,&n);
                if ((lo>>i)&1) {
                        fc(10, &n);     fc(8,  &n);             // low-high transition
                } else {
                        fc(8,  &n);     fc(10, &n);             // high-low transition
                }
        }

        if (ledcontrol)
                LED_A_ON();
        SimulateTagLowFrequency(n, 0, ledcontrol);

        if (ledcontrol)
                LED_A_OFF();
}


// loop to capture raw HID waveform then FSK demodulate the TAG ID from it
void CmdHIDdemodFSK(int findone, int *high, int *low, int ledcontrol)
{
        uint8_t *dest = (uint8_t *)BigBuf;
        int m=0, n=0, i=0, idx=0, found=0, lastval=0;
  uint32_t hi2=0, hi=0, lo=0;

        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);

        // Connect the A/D to the peak-detected low-frequency path.
        SetAdcMuxFor(GPIO_MUXSEL_LOPKD);

        // Give it a bit of time for the resonant antenna to settle.
        SpinDelay(50);

        // Now set up the SSC to get the ADC samples that are now streaming at us.
        FpgaSetupSsc();

        for(;;) {
                WDT_HIT();
                if (ledcontrol)
                        LED_A_ON();
                if(BUTTON_PRESS()) {
                        DbpString("Stopped");
                        if (ledcontrol)
                                LED_A_OFF();
                        return;
                }

                i = 0;
                m = sizeof(BigBuf);
                memset(dest,128,m);
                for(;;) {
                        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
                                AT91C_BASE_SSC->SSC_THR = 0x43;
                                if (ledcontrol)
                                        LED_D_ON();
                        }
                        if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
                                dest[i] = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                                // we don't care about actual value, only if it's more or less than a
                                // threshold essentially we capture zero crossings for later analysis
                                if(dest[i] < 127) dest[i] = 0; else dest[i] = 1;
                                i++;
                                if (ledcontrol)
                                        LED_D_OFF();
                                if(i >= m) {
                                        break;
                                }
                        }
                }

                // FSK demodulator

                // sync to first lo-hi transition
                for( idx=1; idx<m; idx++) {
                        if (dest[idx-1]<dest[idx])
                                lastval=idx;
                                break;
                }
                WDT_HIT();

                // 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( i=0; idx<m; idx++) {
                        if (dest[idx-1]<dest[idx]) {
                                dest[i]=idx-lastval;
                                if (dest[i] <= 8) {
                                                dest[i]=1;
                                } else {
                                                dest[i]=0;
                                }

                                lastval=idx;
                                i++;
                        }
                }
                m=i;
                WDT_HIT();

                // we now have a set of cycle counts, loop over previous results and aggregate data into bit patterns
                lastval=dest[0];
                idx=0;
                i=0;
                n=0;
                for( idx=0; idx<m; idx++) {
                        if (dest[idx]==lastval) {
                                n++;
                        } else {
                                // a bit time is five fc/10 or six fc/8 cycles so figure out how many bits a pattern width represents,
                                // an extra fc/8 pattern preceeds every 4 bits (about 200 cycles) just to complicate things but it gets
                                // swallowed up by rounding
                                // expected results are 1 or 2 bits, any more and it's an invalid manchester encoding
                                // special start of frame markers use invalid manchester states (no transitions) by using sequences
                                // like 111000
                                if (dest[idx-1]) {
                                        n=(n+1)/6;                      // fc/8 in sets of 6
                                } else {
                                        n=(n+1)/5;                      // fc/10 in sets of 5
                                }
                                switch (n) {                    // stuff appropriate bits in buffer
                                        case 0:
                                        case 1: // one bit
                                                dest[i++]=dest[idx-1];
                                                break;
                                        case 2: // two bits
                                                dest[i++]=dest[idx-1];
                                                dest[i++]=dest[idx-1];
                                                break;
                                        case 3: // 3 bit start of frame markers
                                                dest[i++]=dest[idx-1];
                                                dest[i++]=dest[idx-1];
                                                dest[i++]=dest[idx-1];
                                                break;
                                        // When a logic 0 is immediately followed by the start of the next transmisson
                                        // (special pattern) a pattern of 4 bit duration lengths is created.
                                        case 4:
                                                dest[i++]=dest[idx-1];
                                                dest[i++]=dest[idx-1];
                                                dest[i++]=dest[idx-1];
                                                dest[i++]=dest[idx-1];
                                                break;
                                        default:        // this shouldn't happen, don't stuff any bits
                                                break;
                                }
                                n=0;
                                lastval=dest[idx];
                        }
                }
                m=i;
                WDT_HIT();

                // final loop, go over previously decoded manchester data and decode into usable tag ID
                // 111000 bit pattern represent start of frame, 01 pattern represents a 1 and 10 represents a 0
                for( idx=0; idx<m-6; idx++) {
                        // search for a start of frame marker
                        if ( dest[idx] && dest[idx+1] && dest[idx+2] && (!dest[idx+3]) && (!dest[idx+4]) && (!dest[idx+5]) )
                        {
                                found=1;
                                idx+=6;
        if (found && (hi2|hi|lo)) {
          if (hi2 != 0){
            Dbprintf("TAG ID: %x%08x%08x (%d)",
                     (unsigned int) hi2, (unsigned int) hi, (unsigned int) lo, (unsigned int) (lo>>1) & 0xFFFF);
          }
          else {
            Dbprintf("TAG ID: %x%08x (%d)",
                     (unsigned int) hi, (unsigned int) lo, (unsigned int) (lo>>1) & 0xFFFF);
          }
                                        /* if we're only looking for one tag */
                                        if (findone)
                                        {
                                                *high = hi;
                                                *low = lo;
                                                return;
                                        }
          hi2=0;
                                        hi=0;
                                        lo=0;
                                        found=0;
                                }
                        }
                        if (found) {
                                if (dest[idx] && (!dest[idx+1]) ) {
          hi2=(hi2<<1)|(hi>>31);
                                        hi=(hi<<1)|(lo>>31);
                                        lo=(lo<<1)|0;
                                } else if ( (!dest[idx]) && dest[idx+1]) {
          hi2=(hi2<<1)|(hi>>31);
                                        hi=(hi<<1)|(lo>>31);
                                        lo=(lo<<1)|1;
                                } else {
                                        found=0;
          hi2=0;
                                        hi=0;
                                        lo=0;
                                }
                                idx++;
                        }
                        if ( dest[idx] && dest[idx+1] && dest[idx+2] && (!dest[idx+3]) && (!dest[idx+4]) && (!dest[idx+5]) )
                        {
                                found=1;
                                idx+=6;
                                if (found && (hi|lo)) {
          if (hi2 != 0){
            Dbprintf("TAG ID: %x%08x%08x (%d)",
                     (unsigned int) hi2, (unsigned int) hi, (unsigned int) lo, (unsigned int) (lo>>1) & 0xFFFF);
          }
          else {
            Dbprintf("TAG ID: %x%08x (%d)",
                     (unsigned int) hi, (unsigned int) lo, (unsigned int) (lo>>1) & 0xFFFF);
          }
                                        /* if we're only looking for one tag */
                                        if (findone)
                                        {
                                                *high = hi;
                                                *low = lo;
                                                return;
                                        }
          hi2=0;
                                        hi=0;
                                        lo=0;
                                        found=0;
                                }
                        }
                }
                WDT_HIT();
        }
}

/*------------------------------
 * T5555/T5557/T5567 routines
 *------------------------------
 */

/* T55x7 configuration register definitions */
#define T55x7_POR_DELAY                 0x00000001
#define T55x7_ST_TERMINATOR             0x00000008
#define T55x7_PWD                       0x00000010
#define T55x7_MAXBLOCK_SHIFT            5
#define T55x7_AOR                       0x00000200
#define T55x7_PSKCF_RF_2                0
#define T55x7_PSKCF_RF_4                0x00000400
#define T55x7_PSKCF_RF_8                0x00000800
#define T55x7_MODULATION_DIRECT         0
#define T55x7_MODULATION_PSK1           0x00001000
#define T55x7_MODULATION_PSK2           0x00002000
#define T55x7_MODULATION_PSK3           0x00003000
#define T55x7_MODULATION_FSK1           0x00004000
#define T55x7_MODULATION_FSK2           0x00005000
#define T55x7_MODULATION_FSK1a          0x00006000
#define T55x7_MODULATION_FSK2a          0x00007000
#define T55x7_MODULATION_MANCHESTER     0x00008000
#define T55x7_MODULATION_BIPHASE        0x00010000
#define T55x7_BITRATE_RF_8              0
#define T55x7_BITRATE_RF_16             0x00040000
#define T55x7_BITRATE_RF_32             0x00080000
#define T55x7_BITRATE_RF_40             0x000C0000
#define T55x7_BITRATE_RF_50             0x00100000
#define T55x7_BITRATE_RF_64             0x00140000
#define T55x7_BITRATE_RF_100            0x00180000
#define T55x7_BITRATE_RF_128            0x001C0000

/* T5555 (Q5) configuration register definitions */
#define T5555_ST_TERMINATOR             0x00000001
#define T5555_MAXBLOCK_SHIFT            0x00000001
#define T5555_MODULATION_MANCHESTER     0
#define T5555_MODULATION_PSK1           0x00000010
#define T5555_MODULATION_PSK2           0x00000020
#define T5555_MODULATION_PSK3           0x00000030
#define T5555_MODULATION_FSK1           0x00000040
#define T5555_MODULATION_FSK2           0x00000050
#define T5555_MODULATION_BIPHASE        0x00000060
#define T5555_MODULATION_DIRECT         0x00000070
#define T5555_INVERT_OUTPUT             0x00000080
#define T5555_PSK_RF_2                  0
#define T5555_PSK_RF_4                  0x00000100
#define T5555_PSK_RF_8                  0x00000200
#define T5555_USE_PWD                   0x00000400
#define T5555_USE_AOR                   0x00000800
#define T5555_BITRATE_SHIFT             12
#define T5555_FAST_WRITE                0x00004000
#define T5555_PAGE_SELECT               0x00008000

/*
 * Relevant times in microsecond
 * To compensate antenna falling times shorten the write times
 * and enlarge the gap ones.
 */
#define START_GAP 250
#define WRITE_GAP 160
#define WRITE_0   144 // 192
#define WRITE_1   400 // 432 for T55x7; 448 for E5550

// Write one bit to card
void T55xxWriteBit(int bit)
{
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
        if (bit == 0)
                SpinDelayUs(WRITE_0);
        else
                SpinDelayUs(WRITE_1);
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelayUs(WRITE_GAP);
}

// Write one card block in page 0, no lock
void T55xxWriteBlock(uint32_t Data, uint32_t Block, uint32_t Pwd, uint8_t PwdMode)
{
        unsigned int i;

        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);

        // Give it a bit of time for the resonant antenna to settle.
        // And for the tag to fully power up
        SpinDelay(150);

        // Now start writting
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelayUs(START_GAP);

        // Opcode
        T55xxWriteBit(1);
        T55xxWriteBit(0); //Page 0
  if (PwdMode == 1){
    // Pwd
    for (i = 0x80000000; i != 0; i >>= 1)
      T55xxWriteBit(Pwd & i);
  }
        // Lock bit
        T55xxWriteBit(0);

        // Data
        for (i = 0x80000000; i != 0; i >>= 1)
                T55xxWriteBit(Data & i);

        // Block
        for (i = 0x04; i != 0; i >>= 1)
                T55xxWriteBit(Block & i);

        // Now perform write (nominal is 5.6 ms for T55x7 and 18ms for E5550,
        // so wait a little more)
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
        SpinDelay(20);
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
}

// Read one card block in page 0
void T55xxReadBlock(uint32_t Block, uint32_t Pwd, uint8_t PwdMode)
{
        uint8_t *dest = (uint8_t *)BigBuf;
        int m=0, i=0;
  
        m = sizeof(BigBuf);
  // Clear destination buffer before sending the command
        memset(dest, 128, m);
        // Connect the A/D to the peak-detected low-frequency path.
        SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
        // Now set up the SSC to get the ADC samples that are now streaming at us.
        FpgaSetupSsc();
  
        LED_D_ON();
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
  
        // Give it a bit of time for the resonant antenna to settle.
        // And for the tag to fully power up
        SpinDelay(150);
  
        // Now start writting
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelayUs(START_GAP);
  
        // Opcode
        T55xxWriteBit(1);
        T55xxWriteBit(0); //Page 0
        if (PwdMode == 1){
                // Pwd
                for (i = 0x80000000; i != 0; i >>= 1)
                        T55xxWriteBit(Pwd & i);
        }
        // Lock bit
        T55xxWriteBit(0);
        // Block
        for (i = 0x04; i != 0; i >>= 1)
                T55xxWriteBit(Block & i);
  
  // Turn field on to read the response
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
  
        // Now do the acquisition
        i = 0;
        for(;;) {
                if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
                        AT91C_BASE_SSC->SSC_THR = 0x43;
                }
                if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY) {
                        dest[i] = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        // we don't care about actual value, only if it's more or less than a
                        // threshold essentially we capture zero crossings for later analysis
      //                        if(dest[i] < 127) dest[i] = 0; else dest[i] = 1;
                        i++;
                        if (i >= m) break;
                }
        }
  
  FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF); // field off
        LED_D_OFF();
        DbpString("DONE!");
}

// Read card traceability data (page 1)
void T55xxReadTrace(void){
        uint8_t *dest = (uint8_t *)BigBuf;
        int m=0, i=0;
  
        m = sizeof(BigBuf);
  // Clear destination buffer before sending the command
        memset(dest, 128, m);
        // Connect the A/D to the peak-detected low-frequency path.
        SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
        // Now set up the SSC to get the ADC samples that are now streaming at us.
        FpgaSetupSsc();
  
        LED_D_ON();
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
  
        // Give it a bit of time for the resonant antenna to settle.
        // And for the tag to fully power up
        SpinDelay(150);
  
        // Now start writting
        FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
        SpinDelayUs(START_GAP);
  
        // Opcode
        T55xxWriteBit(1);
        T55xxWriteBit(1); //Page 1
  
  // Turn field on to read the response
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
  
        // Now do the acquisition
        i = 0;
        for(;;) {
                if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
                        AT91C_BASE_SSC->SSC_THR = 0x43;
                }
                if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY) {
                        dest[i] = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
                        i++;
                        if (i >= m) break;
                }
        }
  
  FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF); // field off
        LED_D_OFF();
        DbpString("DONE!");
}

/*-------------- Cloning routines -----------*/
// Copy HID id to card and setup block 0 config
void CopyHIDtoT55x7(uint32_t hi2, uint32_t hi, uint32_t lo, uint8_t longFMT)
{
        int data1=0, data2=0, data3=0, data4=0, data5=0, data6=0; //up to six blocks for long format
        int last_block = 0;
  
  if (longFMT){
          // Ensure no more than 84 bits supplied
          if (hi2>0xFFFFF) {
                  DbpString("Tags can only have 84 bits.");
                  return;
          }
    // Build the 6 data blocks for supplied 84bit ID
    last_block = 6;
    data1 = 0x1D96A900; // load preamble (1D) & long format identifier (9E manchester encoded)
          for (int i=0;i<4;i++) {
                  if (hi2 & (1<<(19-i)))
                          data1 |= (1<<(((3-i)*2)+1)); // 1 -> 10
                  else
                          data1 |= (1<<((3-i)*2)); // 0 -> 01
          }
    
        data2 = 0;
        for (int i=0;i<16;i++) {
                if (hi2 & (1<<(15-i)))
                        data2 |= (1<<(((15-i)*2)+1)); // 1 -> 10
                else
                        data2 |= (1<<((15-i)*2)); // 0 -> 01
    }
    
        data3 = 0;
        for (int i=0;i<16;i++) {
                if (hi & (1<<(31-i)))
                        data3 |= (1<<(((15-i)*2)+1)); // 1 -> 10
                else
                        data3 |= (1<<((15-i)*2)); // 0 -> 01
        }
    
        data4 = 0;
        for (int i=0;i<16;i++) {
                if (hi & (1<<(15-i)))
                        data4 |= (1<<(((15-i)*2)+1)); // 1 -> 10
                else
                        data4 |= (1<<((15-i)*2)); // 0 -> 01
    }
    
        data5 = 0;
        for (int i=0;i<16;i++) {
                if (lo & (1<<(31-i)))
                        data5 |= (1<<(((15-i)*2)+1)); // 1 -> 10
                else
                        data5 |= (1<<((15-i)*2)); // 0 -> 01
        }
    
        data6 = 0;
        for (int i=0;i<16;i++) {
                if (lo & (1<<(15-i)))
                        data6 |= (1<<(((15-i)*2)+1)); // 1 -> 10
                else
                        data6 |= (1<<((15-i)*2)); // 0 -> 01
    }
  }
  else {
          // Ensure no more than 44 bits supplied
          if (hi>0xFFF) {
                  DbpString("Tags can only have 44 bits.");
                  return;
          }
    
        // Build the 3 data blocks for supplied 44bit ID
        last_block = 3;
        
        data1 = 0x1D000000; // load preamble
    
    for (int i=0;i<12;i++) {
      if (hi & (1<<(11-i)))
        data1 |= (1<<(((11-i)*2)+1)); // 1 -> 10
      else
        data1 |= (1<<((11-i)*2)); // 0 -> 01
    }
    
        data2 = 0;
        for (int i=0;i<16;i++) {
                if (lo & (1<<(31-i)))
                        data2 |= (1<<(((15-i)*2)+1)); // 1 -> 10
                else
                        data2 |= (1<<((15-i)*2)); // 0 -> 01
        }
    
        data3 = 0;
        for (int i=0;i<16;i++) {
                if (lo & (1<<(15-i)))
                        data3 |= (1<<(((15-i)*2)+1)); // 1 -> 10
                else
                        data3 |= (1<<((15-i)*2)); // 0 -> 01
        }
  }
  
        LED_D_ON();
        // Program the data blocks for supplied ID
        // and the block 0 for HID format
        T55xxWriteBlock(data1,1,0,0);
        T55xxWriteBlock(data2,2,0,0);
        T55xxWriteBlock(data3,3,0,0);
        
        if (longFMT) { // if long format there are 6 blocks
          T55xxWriteBlock(data4,4,0,0);
          T55xxWriteBlock(data5,5,0,0);
          T55xxWriteBlock(data6,6,0,0);
  }
  
        // Config for HID (RF/50, FSK2a, Maxblock=3 for short/6 for long)
        T55xxWriteBlock(T55x7_BITRATE_RF_50    |
                  T55x7_MODULATION_FSK2a |
                  last_block << T55x7_MAXBLOCK_SHIFT,
                  0,0,0);
  
        LED_D_OFF();
        
        DbpString("DONE!");
}

// Define 9bit header for EM410x tags
#define EM410X_HEADER           0x1FF
#define EM410X_ID_LENGTH        40

void WriteEM410x(uint32_t card, uint32_t id_hi, uint32_t id_lo)
{
        int i, id_bit;
        uint64_t id = EM410X_HEADER;
        uint64_t rev_id = 0;    // reversed ID
        int c_parity[4];        // column parity
        int r_parity = 0;       // row parity

        // Reverse ID bits given as parameter (for simpler operations)
        for (i = 0; i < EM410X_ID_LENGTH; ++i) {
                if (i < 32) {
                        rev_id = (rev_id << 1) | (id_lo & 1);
                        id_lo >>= 1;
                } else {
                        rev_id = (rev_id << 1) | (id_hi & 1);
                        id_hi >>= 1;
                }
        }

        for (i = 0; i < EM410X_ID_LENGTH; ++i) {
                id_bit = rev_id & 1;

                if (i % 4 == 0) {
                        // Don't write row parity bit at start of parsing
                        if (i)
                                id = (id << 1) | r_parity;
                        // Start counting parity for new row
                        r_parity = id_bit;
                } else {
                        // Count row parity
                        r_parity ^= id_bit;
                }

                // First elements in column?
                if (i < 4)
                        // Fill out first elements
                        c_parity[i] = id_bit;
                else
                        // Count column parity
                        c_parity[i % 4] ^= id_bit;

                // Insert ID bit
                id = (id << 1) | id_bit;
                rev_id >>= 1;
        }

        // Insert parity bit of last row
        id = (id << 1) | r_parity;

        // Fill out column parity at the end of tag
        for (i = 0; i < 4; ++i)
                id = (id << 1) | c_parity[i];

        // Add stop bit
        id <<= 1;

        Dbprintf("Started writing %s tag ...", card ? "T55x7":"T5555");
        LED_D_ON();

        // Write EM410x ID
        T55xxWriteBlock((uint32_t)(id >> 32), 1, 0, 0);
        T55xxWriteBlock((uint32_t)id, 2, 0, 0);

        // Config for EM410x (RF/64, Manchester, Maxblock=2)
        if (card)
                // Writing configuration for T55x7 tag
                T55xxWriteBlock(T55x7_BITRATE_RF_64         |
                                T55x7_MODULATION_MANCHESTER |
                                2 << T55x7_MAXBLOCK_SHIFT,
                                0, 0, 0);
        else
                // Writing configuration for T5555(Q5) tag
                T55xxWriteBlock(0x1F << T5555_BITRATE_SHIFT |
                                T5555_MODULATION_MANCHESTER   |
                                2 << T5555_MAXBLOCK_SHIFT,
                                0, 0, 0);

        LED_D_OFF();
        Dbprintf("Tag %s written with 0x%08x%08x\n", card ? "T55x7":"T5555",
                                        (uint32_t)(id >> 32), (uint32_t)id);
}

// Clone Indala 64-bit tag by UID to T55x7
void CopyIndala64toT55x7(int hi, int lo)
{

        //Program the 2 data blocks for supplied 64bit UID
        // and the block 0 for Indala64 format
        T55xxWriteBlock(hi,1,0,0);
        T55xxWriteBlock(lo,2,0,0);
        //Config for Indala (RF/32;PSK1 with RF/2;Maxblock=2)
        T55xxWriteBlock(T55x7_BITRATE_RF_32    |
                        T55x7_MODULATION_PSK1 |
                        2 << T55x7_MAXBLOCK_SHIFT,
                        0, 0, 0);
        //Alternative config for Indala (Extended mode;RF/32;PSK1 with RF/2;Maxblock=2;Inverse data)
//      T5567WriteBlock(0x603E1042,0);

        DbpString("DONE!");

}       

void CopyIndala224toT55x7(int uid1, int uid2, int uid3, int uid4, int uid5, int uid6, int uid7)
{

        //Program the 7 data blocks for supplied 224bit UID
        // and the block 0 for Indala224 format
        T55xxWriteBlock(uid1,1,0,0);
        T55xxWriteBlock(uid2,2,0,0);
        T55xxWriteBlock(uid3,3,0,0);
        T55xxWriteBlock(uid4,4,0,0);
        T55xxWriteBlock(uid5,5,0,0);
        T55xxWriteBlock(uid6,6,0,0);
        T55xxWriteBlock(uid7,7,0,0);
        //Config for Indala (RF/32;PSK1 with RF/2;Maxblock=7)
        T55xxWriteBlock(T55x7_BITRATE_RF_32    |
                        T55x7_MODULATION_PSK1 |
                        7 << T55x7_MAXBLOCK_SHIFT,
                        0,0,0);
        //Alternative config for Indala (Extended mode;RF/32;PSK1 with RF/2;Maxblock=7;Inverse data)
//      T5567WriteBlock(0x603E10E2,0);

        DbpString("DONE!");

}


#define abs(x) ( ((x)<0) ? -(x) : (x) )
#define max(x,y) ( x<y ? y:x)

int DemodPCF7931(uint8_t **outBlocks) {
        uint8_t BitStream[256];
        uint8_t Blocks[8][16];
        uint8_t *GraphBuffer = (uint8_t *)BigBuf;
        int GraphTraceLen = sizeof(BigBuf);
        int i, j, lastval, bitidx, half_switch;
        int clock = 64;
        int tolerance = clock / 8;
        int pmc, block_done;
        int lc, warnings = 0;
        int num_blocks = 0;
        int lmin=128, lmax=128;
        uint8_t dir;
        
        AcquireRawAdcSamples125k(0);
        
        lmin = 64;
        lmax = 192;
        
        i = 2;
        
        /* Find first local max/min */
        if(GraphBuffer[1] > GraphBuffer[0]) {
    while(i < GraphTraceLen) {
      if( !(GraphBuffer[i] > GraphBuffer[i-1]) && GraphBuffer[i] > lmax)
        break;
      i++;
    }
    dir = 0;
        }
        else {
    while(i < GraphTraceLen) {
      if( !(GraphBuffer[i] < GraphBuffer[i-1]) && GraphBuffer[i] < lmin)
        break;
      i++;
    }
    dir = 1;
        }
        
        lastval = i++;
        half_switch = 0;
        pmc = 0;
        block_done = 0;
        
        for (bitidx = 0; i < GraphTraceLen; i++)
        {
    if ( (GraphBuffer[i-1] > GraphBuffer[i] && dir == 1 && GraphBuffer[i] > lmax) || (GraphBuffer[i-1] < GraphBuffer[i] && dir == 0 && GraphBuffer[i] < lmin))
    {
      lc = i - lastval;
      lastval = i;
      
      // Switch depending on lc length:
      // Tolerance is 1/8 of clock rate (arbitrary)
      if (abs(lc-clock/4) < tolerance) {
        // 16T0
        if((i - pmc) == lc) { /* 16T0 was previous one */
          /* It's a PMC ! */
          i += (128+127+16+32+33+16)-1;
          lastval = i;
          pmc = 0;
          block_done = 1;
        }
        else {
          pmc = i;
        }
      } else if (abs(lc-clock/2) < tolerance) {
        // 32TO
        if((i - pmc) == lc) { /* 16T0 was previous one */
          /* It's a PMC ! */
          i += (128+127+16+32+33)-1;
          lastval = i;
          pmc = 0;
          block_done = 1;
        }
        else if(half_switch == 1) {
          BitStream[bitidx++] = 0;
          half_switch = 0;
        }
        else
          half_switch++;
      } else if (abs(lc-clock) < tolerance) {
        // 64TO
        BitStream[bitidx++] = 1;
      } else {
        // Error
        warnings++;
        if (warnings > 10)
        {
          Dbprintf("Error: too many detection errors, aborting.");
          return 0;
        }
      }
      
      if(block_done == 1) {
        if(bitidx == 128) {
          for(j=0; j<16; j++) {
            Blocks[num_blocks][j] = 128*BitStream[j*8+7]+
            64*BitStream[j*8+6]+
            32*BitStream[j*8+5]+
            16*BitStream[j*8+4]+
            8*BitStream[j*8+3]+
            4*BitStream[j*8+2]+
            2*BitStream[j*8+1]+
            BitStream[j*8];
          }
          num_blocks++;
        }
        bitidx = 0;
        block_done = 0;
        half_switch = 0;
      }
      if (GraphBuffer[i-1] > GraphBuffer[i]) dir=0;
      else dir = 1;
    }
    if(bitidx==255)
      bitidx=0;
    warnings = 0;
    if(num_blocks == 4) break;
        }
        memcpy(outBlocks, Blocks, 16*num_blocks);
        return num_blocks;
}

int IsBlock0PCF7931(uint8_t *Block) {
        // Assume RFU means 0 :)
        if((memcmp(Block, "\x00\x00\x00\x00\x00\x00\x00\x01", 8) == 0) && memcmp(Block+9, "\x00\x00\x00\x00\x00\x00\x00", 7) == 0) // PAC enabled
    return 1;
        if((memcmp(Block+9, "\x00\x00\x00\x00\x00\x00\x00", 7) == 0) && Block[7] == 0) // PAC disabled, can it *really* happen ?
    return 1;
        return 0;
}

int IsBlock1PCF7931(uint8_t *Block) {
        // Assume RFU means 0 :)
        if(Block[10] == 0 && Block[11] == 0 && Block[12] == 0 && Block[13] == 0)
    if((Block[14] & 0x7f) <= 9 && Block[15] <= 9)
      return 1;
        
        return 0;
}

#define ALLOC 16

void ReadPCF7931() {
        uint8_t Blocks[8][17];
        uint8_t tmpBlocks[4][16];
        int i, j, ind, ind2, n;
        int num_blocks = 0;
        int max_blocks = 8;
        int ident = 0;
        int error = 0;
        int tries = 0;
        
        memset(Blocks, 0, 8*17*sizeof(uint8_t));
        
        do {
    memset(tmpBlocks, 0, 4*16*sizeof(uint8_t));
    n = DemodPCF7931((uint8_t**)tmpBlocks);
    if(!n)
      error++;
    if(error==10 && num_blocks == 0) {
      Dbprintf("Error, no tag or bad tag");
      return;
    }
    else if (tries==20 || error==10) {
      Dbprintf("Error reading the tag");
      Dbprintf("Here is the partial content");
      goto end;
    }
    
    for(i=0; i<n; i++)
      Dbprintf("(dbg) %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x",
               tmpBlocks[i][0], tmpBlocks[i][1], tmpBlocks[i][2], tmpBlocks[i][3], tmpBlocks[i][4], tmpBlocks[i][5], tmpBlocks[i][6], tmpBlocks[i][7],
               tmpBlocks[i][8], tmpBlocks[i][9], tmpBlocks[i][10], tmpBlocks[i][11], tmpBlocks[i][12], tmpBlocks[i][13], tmpBlocks[i][14], tmpBlocks[i][15]);
    if(!ident) {
      for(i=0; i<n; i++) {
        if(IsBlock0PCF7931(tmpBlocks[i])) {
          // Found block 0 ?
          if(i < n-1 && IsBlock1PCF7931(tmpBlocks[i+1])) {
            // Found block 1!
            // \o/
            ident = 1;
            memcpy(Blocks[0], tmpBlocks[i], 16);
            Blocks[0][ALLOC] = 1;
            memcpy(Blocks[1], tmpBlocks[i+1], 16);
            Blocks[1][ALLOC] = 1;
            max_blocks = max((Blocks[1][14] & 0x7f), Blocks[1][15]) + 1;
            // Debug print
            Dbprintf("(dbg) Max blocks: %d", max_blocks);
            num_blocks = 2;
            // Handle following blocks
            for(j=i+2, ind2=2; j!=i; j++, ind2++, num_blocks++) {
              if(j==n) j=0;
              if(j==i) break;
              memcpy(Blocks[ind2], tmpBlocks[j], 16);
              Blocks[ind2][ALLOC] = 1;
            }
            break;
          }
        }
      }
    }
    else {
      for(i=0; i<n; i++) { // Look for identical block in known blocks
        if(memcmp(tmpBlocks[i], "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 16)) { // Block is not full of 00
          for(j=0; j<max_blocks; j++) {
            if(Blocks[j][ALLOC] == 1 && !memcmp(tmpBlocks[i], Blocks[j], 16)) {
              // Found an identical block
              for(ind=i-1,ind2=j-1; ind >= 0; ind--,ind2--) {
                if(ind2 < 0)
                  ind2 = max_blocks;
                if(!Blocks[ind2][ALLOC]) { // Block ind2 not already found
                  // Dbprintf("Tmp %d -> Block %d", ind, ind2);
                  memcpy(Blocks[ind2], tmpBlocks[ind], 16);
                  Blocks[ind2][ALLOC] = 1;
                  num_blocks++;
                  if(num_blocks == max_blocks) goto end;
                }
              }
              for(ind=i+1,ind2=j+1; ind < n; ind++,ind2++) {
                if(ind2 > max_blocks)
                  ind2 = 0;
                if(!Blocks[ind2][ALLOC]) { // Block ind2 not already found
                  // Dbprintf("Tmp %d -> Block %d", ind, ind2);
                  memcpy(Blocks[ind2], tmpBlocks[ind], 16);
                  Blocks[ind2][ALLOC] = 1;
                  num_blocks++;
                  if(num_blocks == max_blocks) goto end;
                }
              }
            }
          }
        }
      }
    }
    tries++;
    if (BUTTON_PRESS()) return;
        } while (num_blocks != max_blocks);
end:
        Dbprintf("-----------------------------------------");
        Dbprintf("Memory content:");
        Dbprintf("-----------------------------------------");
        for(i=0; i<max_blocks; i++) {
    if(Blocks[i][ALLOC]==1)
      Dbprintf("%02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x",
               Blocks[i][0], Blocks[i][1], Blocks[i][2], Blocks[i][3], Blocks[i][4], Blocks[i][5], Blocks[i][6], Blocks[i][7],
               Blocks[i][8], Blocks[i][9], Blocks[i][10], Blocks[i][11], Blocks[i][12], Blocks[i][13], Blocks[i][14], Blocks[i][15]);
    else
      Dbprintf("<missing block %d>", i);
        }
        Dbprintf("-----------------------------------------");
        
        return ;
}


//-----------------------------------
// EM4469 / EM4305 routines
//-----------------------------------
#define FWD_CMD_LOGIN 0xC //including the even parity, binary mirrored
#define FWD_CMD_WRITE 0xA
#define FWD_CMD_READ 0x9
#define FWD_CMD_DISABLE 0x5


uint8_t forwardLink_data[64]; //array of forwarded bits
uint8_t * forward_ptr; //ptr for forward message preparation
uint8_t fwd_bit_sz; //forwardlink bit counter
uint8_t * fwd_write_ptr; //forwardlink bit pointer

//====================================================================
// prepares command bits
// see EM4469 spec
//====================================================================
//--------------------------------------------------------------------
uint8_t Prepare_Cmd( uint8_t cmd ) {
  //--------------------------------------------------------------------
  
  *forward_ptr++ = 0; //start bit
  *forward_ptr++ = 0; //second pause for 4050 code
  
  *forward_ptr++ = cmd;
  cmd >>= 1;
  *forward_ptr++ = cmd;
  cmd >>= 1;
  *forward_ptr++ = cmd;
  cmd >>= 1;
  *forward_ptr++ = cmd;
  
  return 6; //return number of emited bits
}

//====================================================================
// prepares address bits
// see EM4469 spec
//====================================================================

//--------------------------------------------------------------------
uint8_t Prepare_Addr( uint8_t addr ) {
  //--------------------------------------------------------------------
  
  register uint8_t line_parity;
  
  uint8_t i;
  line_parity = 0;
  for(i=0;i<6;i++) {
    *forward_ptr++ = addr;
    line_parity ^= addr;
    addr >>= 1;
  }
  
  *forward_ptr++ = (line_parity & 1);
  
  return 7; //return number of emited bits
}

//====================================================================
// prepares data bits intreleaved with parity bits
// see EM4469 spec
//====================================================================

//--------------------------------------------------------------------
uint8_t Prepare_Data( uint16_t data_low, uint16_t data_hi) {
  //--------------------------------------------------------------------
  
  register uint8_t line_parity;
  register uint8_t column_parity;
  register uint8_t i, j;
  register uint16_t data;
  
  data = data_low;
  column_parity = 0;
  
  for(i=0; i<4; i++) {
    line_parity = 0;
    for(j=0; j<8; j++) {
      line_parity ^= data;
      column_parity ^= (data & 1) << j;
      *forward_ptr++ = data;
      data >>= 1;
    }
    *forward_ptr++ = line_parity;
    if(i == 1)
      data = data_hi;
  }
  
  for(j=0; j<8; j++) {
    *forward_ptr++ = column_parity;
    column_parity >>= 1;
  }
  *forward_ptr = 0;
  
  return 45; //return number of emited bits
}

//====================================================================
// Forward Link send function
// Requires: forwarLink_data filled with valid bits (1 bit per byte)
// fwd_bit_count set with number of bits to be sent
//====================================================================
void SendForward(uint8_t fwd_bit_count) {
  
  fwd_write_ptr = forwardLink_data;
  fwd_bit_sz = fwd_bit_count;
  
  LED_D_ON();
  
  //Field on
  FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
  FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
  
  // Give it a bit of time for the resonant antenna to settle.
  // And for the tag to fully power up
  SpinDelay(150);
  
  // force 1st mod pulse (start gap must be longer for 4305)
  fwd_bit_sz--; //prepare next bit modulation
  fwd_write_ptr++;
  FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF); // field off
  SpinDelayUs(55*8); //55 cycles off (8us each)for 4305
  FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
  FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);//field on
  SpinDelayUs(16*8); //16 cycles on (8us each)
  
  // now start writting
  while(fwd_bit_sz-- > 0) { //prepare next bit modulation
    if(((*fwd_write_ptr++) & 1) == 1)
      SpinDelayUs(32*8); //32 cycles at 125Khz (8us each)
    else {
      //These timings work for 4469/4269/4305 (with the 55*8 above)
      FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF); // field off
      SpinDelayUs(23*8); //16-4 cycles off (8us each)
      FpgaSendCommand(FPGA_CMD_SET_DIVISOR, 95); //125Khz
      FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);//field on
      SpinDelayUs(9*8); //16 cycles on (8us each)
    }
  }
}

void EM4xLogin(uint32_t Password) {
  
  uint8_t fwd_bit_count;
  
  forward_ptr = forwardLink_data;
  fwd_bit_count = Prepare_Cmd( FWD_CMD_LOGIN );
  fwd_bit_count += Prepare_Data( Password&0xFFFF, Password>>16 );
  
  SendForward(fwd_bit_count);
  
  //Wait for command to complete
  SpinDelay(20);
  
}

void EM4xReadWord(uint8_t Address, uint32_t Pwd, uint8_t PwdMode) {
  
  uint8_t fwd_bit_count;
  uint8_t *dest = (uint8_t *)BigBuf;
  int m=0, i=0;
  
  //If password mode do login
  if (PwdMode == 1) EM4xLogin(Pwd);
  
  forward_ptr = forwardLink_data;
  fwd_bit_count = Prepare_Cmd( FWD_CMD_READ );
  fwd_bit_count += Prepare_Addr( Address );
  
  m = sizeof(BigBuf);
  // Clear destination buffer before sending the command
  memset(dest, 128, m);
  // Connect the A/D to the peak-detected low-frequency path.
  SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
  // Now set up the SSC to get the ADC samples that are now streaming at us.
  FpgaSetupSsc();
  
  SendForward(fwd_bit_count);
  
  // Now do the acquisition
  i = 0;
  for(;;) {
    if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
      AT91C_BASE_SSC->SSC_THR = 0x43;
    }
    if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY) {
      dest[i] = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
      i++;
      if (i >= m) break;
    }
  }
  FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF); // field off
  LED_D_OFF();
}

void EM4xWriteWord(uint32_t Data, uint8_t Address, uint32_t Pwd, uint8_t PwdMode) {
  
  uint8_t fwd_bit_count;
  
  //If password mode do login
  if (PwdMode == 1) EM4xLogin(Pwd);
  
  forward_ptr = forwardLink_data;
  fwd_bit_count = Prepare_Cmd( FWD_CMD_WRITE );
  fwd_bit_count += Prepare_Addr( Address );
  fwd_bit_count += Prepare_Data( Data&0xFFFF, Data>>16 );
  
  SendForward(fwd_bit_count);
  
  //Wait for write to complete
  SpinDelay(20);
  FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF); // field off
  LED_D_OFF();
}