Add command and code for bidirectional LF emulation of Hitag2. Should be extended for other types of tags

armsrc/Makefile

@@ -14,6 +14,7 @@ THUMBSRC = start.c \
 	iso15693.c \
 	util.c \
 	version.c \
+	hitag2.c \
 	usb.c
 
 # These are to be compiled in ARM mode

armsrc/appmain.c

@@ -645,6 +645,9 @@ void UsbPacketReceived(BYTE *packet, int len)
 		case CMD_VERSION:
 			SendVersion();
 			break;
+		case CMD_LF_SIMULATE_BIDIR:
+			SimulateTagLowFrequencyBidir(c->ext1, c->ext2);
+			break;
 #ifdef WITH_LCD
 		case CMD_LCD_RESET:
 			LCDReset();

armsrc/apps.h

@@ -74,6 +74,7 @@ void AcquireRawBitsTI(void);
 void SimulateTagLowFrequency(int period, int ledcontrol);
 void CmdHIDsimTAG(int hi, int lo, int ledcontrol);
 void CmdHIDdemodFSK(int findone, int *high, int *low, int ledcontrol);
+void SimulateTagLowFrequencyBidir(int divisor, int max_bitlen);
 
 /// iso14443.h
 void SimulateIso14443Tag(void);

armsrc/lfops.c

@@ -6,6 +6,7 @@
 //-----------------------------------------------------------------------------
 #include <proxmark3.h>
 #include "apps.h"
+#include "hitag2.h"
 #include "../common/crc16.c"
 
 void AcquireRawAdcSamples125k(BOOL at134khz)
@@ -61,6 +62,10 @@ void ModThenAcquireRawAdcSamples125k(int delay_off,int period_0,int period_1,BYT
 {
 	BOOL 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;
@@ -77,6 +82,8 @@ void ModThenAcquireRawAdcSamples125k(int delay_off,int period_0,int period_1,BYT
 
 	// 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();
@@ -95,11 +102,12 @@ void ModThenAcquireRawAdcSamples125k(int delay_off,int period_0,int period_1,BYT
 			FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_READER);
 		}
 		LED_D_ON();
-		if(*(command++) == '0')
+		if(*(command++) == '0') {
 			SpinDelayUs(period_0);
-		else
+		} else {
 			SpinDelayUs(period_1);
 		}
+		}
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
 	LED_D_OFF();
 	SpinDelayUs(delay_off);
@@ -478,6 +486,195 @@ void SimulateTagLowFrequency(int period, int ledcontrol)
 	}
 }
 
+/* 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)
+	 */
+	
+	PMC_PERIPHERAL_CLK_ENABLE = (1 << PERIPH_TC1);
+	PIO_PERIPHERAL_B_SEL = (1 << GPIO_SSC_FRAME);
+	TC1_CCR = TC_CCR_CLKDIS;
+	TC1_CMR = TC_CMR_TCCLKS_TIMER_CLOCK1 | TC_CMR_ETRGEDG_RISING | TC_CMR_ABETRG |
+		TC_CMR_LDRA_RISING | TC_CMR_LDRB_RISING;
+	TC1_CCR = TC_CCR_CLKEN | TC_CCR_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(TC1_SR & TC_SR_LDRAS) {
+			int ra = TC1_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(TC1_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(TC1_CV < t0*15);
+		OPEN_COIL();
+		while(TC1_CV < t0*31);
+		LED_A_OFF();
+	} else if(bit == 0) {
+		/* Manchester: Unloaded, then loaded */
+		LED_B_ON();
+		OPEN_COIL();
+		while(TC1_CV < t0*15);
+		SHORT_COIL();
+		while(TC1_CV < t0*31);
+		LED_B_OFF();
+	}
+	TC1_CCR = TC_CCR_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();
+	PIO_OUTPUT_ENABLE = (1 << 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(TC1_CV < t0*(fdt-8));
+
+	int saved_cmr = TC1_CMR;
+	TC1_CMR &= ~TC_CMR_ETRGEDG; /* Disable external trigger for the clock */
+	TC1_CCR = TC_CCR_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();
+	TC1_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) {
 	BYTE *dest = (BYTE *)BigBuf;

include/usb_cmd.h

@@ -50,6 +50,7 @@ typedef struct {
 #define CMD_HID_DEMOD_FSK															0x020B
 #define CMD_HID_SIM_TAG																0x020C
 #define CMD_SET_LF_DIVISOR														0x020D
+#define CMD_LF_SIMULATE_BIDIR														0x020E
 
 // For the 13.56 MHz tags
 #define CMD_ACQUIRE_RAW_ADC_SAMPLES_ISO_15693					0x0300

winsrc/command.cpp

@@ -663,6 +663,15 @@ static void CmdLosim(char *str)
 	SendCommand(&c, FALSE);
 }
 
+static void CmdLosimBidir(char *str)
+{
+	UsbCommand c;
+	c.cmd = CMD_LF_SIMULATE_BIDIR;
+	c.ext1 = 47; /* Set ADC to twice the carrier for a slight supersampling */
+	c.ext2 = 384;
+	SendCommand(&c, FALSE);
+}
+
 static void CmdLoread(char *str)
 {
 	UsbCommand c;
@@ -2834,6 +2843,7 @@ static struct {
 	{"loread",				CmdLoread,					0, "['h'] -- Read 125/134 kHz LF ID-only tag (option 'h' for 134)"},
 	{"losamples",			CmdLosamples,				0, "[128 - 16000] -- Get raw samples for LF tag"},
 	{"losim",					CmdLosim,						0, "Simulate LF tag"},
+	{"losimbidir",					CmdLosimBidir,						0, "Simulate LF tag (with bidirectional data transmission between reader and tag)"},
 	{"ltrim",					CmdLtrim,						1, "<samples> -- Trim samples from left of trace"},
 	{"mandemod",			Cmdmanchesterdemod,	1, "[i] [clock rate] -- Manchester demodulate binary stream (option 'i' to invert output)"},
 	{"manmod",				Cmdmanchestermod,		1, "[clock rate] -- Manchester modulate a binary stream"},