setting svn:eol-style=native on files, part 1

[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_SIMULATOR);

        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);
                        }
                }
        }
}

/* Provides a framework for bidirectional LF tag communication
 * Encoding is currently Hitag2, but the general idea can probably
 * be transferred to other encodings.
 *
 * The new FPGA code will, for the LF simulator mode, give on SSC_FRAME
 * (PA15) a thresholded version of the signal from the ADC. Setting the
 * ADC path to the low frequency peak detection signal, will enable a
 * somewhat reasonable receiver for modulation on the carrier signal
 * that is generated by the reader. The signal is low when the reader
 * field is switched off, and high when the reader field is active. Due
 * to the way that the signal looks like, mostly only the rising edge is
 * useful, your mileage may vary.
 *
 * Neat perk: PA15 can not only be used as a bit-banging GPIO, but is also
 * TIOA1, which can be used as the capture input for timer 1. This should
 * make it possible to measure the exact edge-to-edge time, without processor
 * intervention.
 *
 * Arguments: divisor is the divisor to be sent to the FPGA (e.g. 95 for 125kHz)
 * t0 is the carrier frequency cycle duration in terms of MCK (384 for 125kHz)
 *
 * The following defines are in carrier periods:
 */
#define HITAG_T_0_MIN 15 /* T[0] should be 18..22 */
#define HITAG_T_1_MIN 24 /* T[1] should be 26..30 */
#define HITAG_T_EOF   40 /* T_EOF should be > 36 */
#define HITAG_T_WRESP 208 /* T_wresp should be 204..212 */

static void hitag_handle_frame(int t0, int frame_len, char *frame);
//#define DEBUG_RA_VALUES 1
#define DEBUG_FRAME_CONTENTS 1
void SimulateTagLowFrequencyBidir(int divisor, int t0)
{
#if DEBUG_RA_VALUES || DEBUG_FRAME_CONTENTS
        int i = 0;
#endif
        char frame[10];
        int frame_pos=0;

        DbpString("Starting Hitag2 emulator, press button to end");
        hitag2_init();

        /* Set up simulator mode, frequency divisor which will drive the FPGA
         * and analog mux selection.
         */
        FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_SIMULATOR);
        FpgaSendCommand(FPGA_CMD_SET_DIVISOR, divisor);
        SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
        RELAY_OFF();

        /* Set up Timer 1:
         * Capture mode, timer source MCK/2 (TIMER_CLOCK1), TIOA is external trigger,
         * external trigger rising edge, load RA on rising edge of TIOA, load RB on rising
         * edge of TIOA. Assign PA15 to TIOA1 (peripheral B)
         */

        AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC1);
        AT91C_BASE_PIOA->PIO_BSR = GPIO_SSC_FRAME;
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
        AT91C_BASE_TC1->TC_CMR =        TC_CMR_TCCLKS_TIMER_CLOCK1 |
                                                                AT91C_TC_ETRGEDG_RISING |
                                                                AT91C_TC_ABETRG |
                                                                AT91C_TC_LDRA_RISING |
                                                                AT91C_TC_LDRB_RISING;
        AT91C_BASE_TC1->TC_CCR =        AT91C_TC_CLKEN |
                                                                AT91C_TC_SWTRG;

        /* calculate the new value for the carrier period in terms of TC1 values */
        t0 = t0/2;

        int overflow = 0;
        while(!BUTTON_PRESS()) {
                WDT_HIT();
                if(AT91C_BASE_TC1->TC_SR & AT91C_TC_LDRAS) {
                        int ra = AT91C_BASE_TC1->TC_RA;
                        if((ra > t0*HITAG_T_EOF) | overflow) ra = t0*HITAG_T_EOF+1;
#if DEBUG_RA_VALUES
                        if(ra > 255 || overflow) ra = 255;
                        ((char*)BigBuf)[i] = ra;
                        i = (i+1) % 8000;
#endif

                        if(overflow || (ra > t0*HITAG_T_EOF) || (ra < t0*HITAG_T_0_MIN)) {
                                /* Ignore */
                        } else if(ra >= t0*HITAG_T_1_MIN ) {
                                /* '1' bit */
                                if(frame_pos < 8*sizeof(frame)) {
                                        frame[frame_pos / 8] |= 1<<( 7-(frame_pos%8) );
                                        frame_pos++;
                                }
                        } else if(ra >= t0*HITAG_T_0_MIN) {
                                /* '0' bit */
                                if(frame_pos < 8*sizeof(frame)) {
                                        frame[frame_pos / 8] |= 0<<( 7-(frame_pos%8) );
                                        frame_pos++;
                                }
                        }

                        overflow = 0;
                        LED_D_ON();
                } else {
                        if(AT91C_BASE_TC1->TC_CV > t0*HITAG_T_EOF) {
                                /* Minor nuisance: In Capture mode, the timer can not be
                                 * stopped by a Compare C. There's no way to stop the clock
                                 * in software, so we'll just have to note the fact that an
                                 * overflow happened and the next loaded timer value might
                                 * have wrapped. Also, this marks the end of frame, and the
                                 * still running counter can be used to determine the correct
                                 * time for the start of the reply.
                                 */
                                overflow = 1;

                                if(frame_pos > 0) {
                                        /* Have a frame, do something with it */
#if DEBUG_FRAME_CONTENTS
                                        ((char*)BigBuf)[i++] = frame_pos;
                                        memcpy( ((char*)BigBuf)+i, frame, 7);
                                        i+=7;
                                        i = i % sizeof(BigBuf);
#endif
                                        hitag_handle_frame(t0, frame_pos, frame);
                                        memset(frame, 0, sizeof(frame));
                                }
                                frame_pos = 0;

                        }
                        LED_D_OFF();
                }
        }
        DbpString("All done");
}

static void hitag_send_bit(int t0, int bit) {
        if(bit == 1) {
                /* Manchester: Loaded, then unloaded */
                LED_A_ON();
                SHORT_COIL();
                while(AT91C_BASE_TC1->TC_CV < t0*15);
                OPEN_COIL();
                while(AT91C_BASE_TC1->TC_CV < t0*31);
                LED_A_OFF();
        } else if(bit == 0) {
                /* Manchester: Unloaded, then loaded */
                LED_B_ON();
                OPEN_COIL();
                while(AT91C_BASE_TC1->TC_CV < t0*15);
                SHORT_COIL();
                while(AT91C_BASE_TC1->TC_CV < t0*31);
                LED_B_OFF();
        }
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_SWTRG; /* Reset clock for the next bit */

}
static void hitag_send_frame(int t0, int frame_len, const char const * frame, int fdt)
{
        OPEN_COIL();
        AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;

        /* Wait for HITAG_T_WRESP carrier periods after the last reader bit,
         * not that since the clock counts since the rising edge, but T_wresp is
         * with respect to the falling edge, we need to wait actually (T_wresp - T_g)
         * periods. The gap time T_g varies (4..10).
         */
        while(AT91C_BASE_TC1->TC_CV < t0*(fdt-8));

        int saved_cmr = AT91C_BASE_TC1->TC_CMR;
        AT91C_BASE_TC1->TC_CMR &= ~AT91C_TC_ETRGEDG; /* Disable external trigger for the clock */
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_SWTRG; /* Reset the clock and use it for response timing */

        int i;
        for(i=0; i<5; i++)
                hitag_send_bit(t0, 1); /* Start of frame */

        for(i=0; i<frame_len; i++) {
                hitag_send_bit(t0, !!(frame[i/ 8] & (1<<( 7-(i%8) ))) );
        }

        OPEN_COIL();
        AT91C_BASE_TC1->TC_CMR = saved_cmr;
}

/* Callback structure to cleanly separate tag emulation code from the radio layer. */
static int hitag_cb(const char* response_data, const int response_length, const int fdt, void *cb_cookie)
{
        hitag_send_frame(*(int*)cb_cookie, response_length, response_data, fdt);
        return 0;
}
/* Frame length in bits, frame contents in MSBit first format */
static void hitag_handle_frame(int t0, int frame_len, char *frame)
{
        hitag2_handle_command(frame, frame_len, hitag_cb, &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 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 && (hi|lo)) {
                                        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;
                                        }
                                        hi=0;
                                        lo=0;
                                        found=0;
                                }
                        }
                        if (found) {
                                if (dest[idx] && (!dest[idx+1]) ) {
                                        hi=(hi<<1)|(lo>>31);
                                        lo=(lo<<1)|0;
                                } else if ( (!dest[idx]) && dest[idx+1]) {
                                        hi=(hi<<1)|(lo>>31);
                                        lo=(lo<<1)|1;
                                } else {
                                        found=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)) {
                                        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;
                                        }
                                        hi=0;
                                        lo=0;
                                        found=0;
                                }
                        }
                }
                WDT_HIT();
        }
}