+/* 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);
+ // 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
+ FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
+ 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;
+ }
+ }
+ }