diff --git a/.gitignore b/.gitignore
index 320f0b71..0c016b75 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,7 @@
 *.hex
 *.srec
 host/build/
+host/**/build
 
 # Operating system spew
 .DS_Store
diff --git a/firmware/blinky/blinky.c b/firmware/blinky/blinky.c
index 143c9940..d3aeea0a 100644
--- a/firmware/blinky/blinky.c
+++ b/firmware/blinky/blinky.c
@@ -36,15 +36,13 @@ int main(void)
 		led_on(LED2);
 		led_on(LED3);
 
-		for (i = 0; i < 2000000; i++)	/* Wait a bit. */
-			__asm__("nop");
+		delay(2000000);
 		
 		led_off(LED1);
 		led_off(LED2);
 		led_off(LED3);
 		
-		for (i = 0; i < 2000000; i++)	/* Wait a bit. */
-			__asm__("nop");
+		delay(2000000);
 	}
 
 	return 0;
diff --git a/firmware/common/hackrf_core.c b/firmware/common/hackrf_core.c
index 6e116bc8..6212c974 100644
--- a/firmware/common/hackrf_core.c
+++ b/firmware/common/hackrf_core.c
@@ -85,6 +85,17 @@ static struct gpio_t gpio_rffc5072_select	= GPIO(2, 13);
 static struct gpio_t gpio_rffc5072_clock	= GPIO(5,  6);
 static struct gpio_t gpio_rffc5072_data		= GPIO(3,  3);
 static struct gpio_t gpio_rffc5072_reset	= GPIO(2, 14);
+
+/*
+static struct gpio_t gpio_sync_in_a		= GPIO(3,  8);
+static struct gpio_t gpio_sync_in_b		= GPIO(3,  9);
+static struct gpio_t gpio_sync_out_a		= GPIO(3, 10);
+static struct gpio_t gpio_sync_out_b		= GPIO(3, 11);
+*/
+static struct gpio_t gpio_sync_in_a		= GPIO(3,  10);
+static struct gpio_t gpio_sync_in_b		= GPIO(3,  11);
+static struct gpio_t gpio_sync_out_a		= GPIO(3, 8);
+static struct gpio_t gpio_sync_out_b		= GPIO(3, 9);
 #endif
 
 /* RF LDO control */
@@ -841,6 +852,15 @@ void pin_setup(void) {
 
 	/* Safe state: start with VAA turned off: */
 	disable_rf_power();
+
+	scu_pinmux(SCU_PINMUX_GPIO3_10, SCU_GPIO_PDN | SCU_CONF_FUNCTION0);
+	scu_pinmux(SCU_PINMUX_GPIO3_11, SCU_GPIO_PDN | SCU_CONF_FUNCTION0);
+
+	gpio_input(&gpio_sync_in_a);
+	gpio_input(&gpio_sync_in_b);
+
+	gpio_output(&gpio_sync_out_a);
+	gpio_output(&gpio_sync_out_b);
 #endif
 
 	/* enable input on SCL and SDA pins */
@@ -886,3 +906,34 @@ void led_off(const led_t led) {
 void led_toggle(const led_t led) {
 	gpio_toggle(&gpio_led[led]);
 }
+
+void hw_sync_syn() {
+	gpio_set(&gpio_sync_out_a);
+}
+
+void hw_sync_stop() {
+	gpio_clear(&gpio_sync_out_a);
+	gpio_clear(&gpio_sync_out_b);
+}
+
+void hw_sync_ack() {
+	gpio_set(&gpio_sync_out_b);
+}
+
+void hw_sync_copy_state() {
+	if(gpio_read(&gpio_sync_in_a)) {
+		gpio_set(&gpio_sync_out_a);
+	} else {
+		gpio_clear(&gpio_sync_out_a);
+	}
+	if(gpio_read(&gpio_sync_in_b)) {
+		gpio_set(&gpio_sync_out_b);
+	} else {
+		gpio_clear(&gpio_sync_out_b);
+	}
+}
+
+bool hw_sync_ready() {
+	return (gpio_read(&gpio_sync_in_a) && gpio_read(&gpio_sync_in_b));
+}
+
diff --git a/firmware/common/hackrf_core.h b/firmware/common/hackrf_core.h
index 974fa5ee..8b4e8316 100644
--- a/firmware/common/hackrf_core.h
+++ b/firmware/common/hackrf_core.h
@@ -225,6 +225,11 @@ typedef enum {
 	TRANSCEIVER_MODE_CPLD_UPDATE = 4
 } transceiver_mode_t;
 
+typedef enum {
+	HW_SYNC_MODE_OFF = 0,
+	HW_SYNC_MODE_ON = 1,
+} hw_sync_mode_t;
+
 void delay(uint32_t duration);
 
 /* TODO: Hide these configurations */
@@ -272,6 +277,13 @@ void led_on(const led_t led);
 void led_off(const led_t led);
 void led_toggle(const led_t led);
 
+void hw_sync_syn();
+void hw_sync_stop();
+void hw_sync_ack();
+bool hw_sync_ready();
+void hw_sync_copy_state();
+
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/firmware/common/streaming.c b/firmware/common/streaming.c
index 07db7b64..61105f76 100644
--- a/firmware/common/streaming.c
+++ b/firmware/common/streaming.c
@@ -37,4 +37,4 @@ void baseband_streaming_disable(sgpio_config_t* const sgpio_config) {
 	sgpio_cpld_stream_disable(sgpio_config);
 
 	nvic_disable_irq(NVIC_SGPIO_IRQ);
-}
\ No newline at end of file
+}
diff --git a/firmware/hackrf_usb/hackrf_usb.c b/firmware/hackrf_usb/hackrf_usb.c
index 046934c7..c82bf179 100644
--- a/firmware/hackrf_usb/hackrf_usb.c
+++ b/firmware/hackrf_usb/hackrf_usb.c
@@ -43,7 +43,6 @@
 #include "usb_api_operacake.h"
 #include "operacake.h"
 #include "usb_api_sweep.h"
-
 #include "usb_api_transceiver.h"
 #include "usb_bulk_buffer.h"
  
@@ -80,7 +79,8 @@ static const usb_request_handler_fn vendor_request_handler[] = {
 	usb_vendor_request_read_wcid,  // USB_WCID_VENDOR_REQ
 	usb_vendor_request_init_sweep,
 	usb_vendor_request_operacake_get_boards,
-	usb_vendor_request_operacake_set_ports
+	usb_vendor_request_operacake_set_ports,
+	usb_vendor_request_set_hw_sync_mode
 };
 
 static const uint32_t vendor_request_handler_count =
@@ -193,6 +193,8 @@ int main(void) {
 			sweep_mode();
 		}
 
+		start_streaming_on_hw_sync();
+
 		// Set up IN transfer of buffer 0.
 		if ( usb_bulk_buffer_offset >= 16384
 		     && phase == 1
diff --git a/firmware/hackrf_usb/usb_api_transceiver.c b/firmware/hackrf_usb/usb_api_transceiver.c
index d86de7db..19178473 100644
--- a/firmware/hackrf_usb/usb_api_transceiver.c
+++ b/firmware/hackrf_usb/usb_api_transceiver.c
@@ -230,7 +230,11 @@ usb_request_status_t usb_vendor_request_set_freq_explicit(
 }
 
 static volatile transceiver_mode_t _transceiver_mode = TRANSCEIVER_MODE_OFF;
+static volatile hw_sync_mode_t _hw_sync_mode = HW_SYNC_MODE_OFF;
 
+void set_hw_sync_mode(const hw_sync_mode_t new_hw_sync_mode) {
+	_hw_sync_mode = new_hw_sync_mode;
+}
 
 transceiver_mode_t transceiver_mode(void) {
 	return _transceiver_mode;
@@ -261,18 +265,27 @@ void set_transceiver_mode(const transceiver_mode_t new_transceiver_mode) {
 		led_off(LED3);
 		rf_path_set_direction(&rf_path, RF_PATH_DIRECTION_OFF);
 		vector_table.irq[NVIC_SGPIO_IRQ] = sgpio_isr_rx;
+
+		hw_sync_stop();
 	}
 
+	hw_sync_stop();
+
 	if( _transceiver_mode != TRANSCEIVER_MODE_OFF ) {
 		si5351c_activate_best_clock_source(&clock_gen);
-		baseband_streaming_enable(&sgpio_config);
+
+		if( _hw_sync_mode != HW_SYNC_MODE_OFF) {
+			hw_sync_syn();
+		} else {
+			baseband_streaming_enable(&sgpio_config);
+		}
 	}
 }
 
 usb_request_status_t usb_vendor_request_set_transceiver_mode(
 	usb_endpoint_t* const endpoint,
-	const usb_transfer_stage_t stage
-) {
+	const usb_transfer_stage_t stage)
+{
 	if( stage == USB_TRANSFER_STAGE_SETUP ) {
 		switch( endpoint->setup.value ) {
 		case TRANSCEIVER_MODE_OFF:
@@ -292,4 +305,28 @@ usb_request_status_t usb_vendor_request_set_transceiver_mode(
 	} else {
 		return USB_REQUEST_STATUS_OK;
 	}
-}
\ No newline at end of file
+}
+
+usb_request_status_t usb_vendor_request_set_hw_sync_mode(
+	usb_endpoint_t* const endpoint,
+	const usb_transfer_stage_t stage)
+{
+	if( stage == USB_TRANSFER_STAGE_SETUP ) {
+		set_hw_sync_mode(endpoint->setup.value);
+		usb_transfer_schedule_ack(endpoint->in);
+		return USB_REQUEST_STATUS_OK;
+	} else {
+		return USB_REQUEST_STATUS_OK;
+	}
+}
+
+void start_streaming_on_hw_sync()
+{
+	if( _hw_sync_mode != HW_SYNC_MODE_OFF) {
+		while(!hw_sync_ready()) { }
+		hw_sync_ack();
+		led_on(LED3);
+
+		baseband_streaming_enable(&sgpio_config);
+	}
+}
diff --git a/firmware/hackrf_usb/usb_api_transceiver.h b/firmware/hackrf_usb/usb_api_transceiver.h
index 59f85778..eb4a5c35 100644
--- a/firmware/hackrf_usb/usb_api_transceiver.h
+++ b/firmware/hackrf_usb/usb_api_transceiver.h
@@ -27,6 +27,7 @@
 #include <usb_type.h>
 #include <usb_request.h>
 
+void set_hw_sync_mode(const hw_sync_mode_t new_hw_sync_mode);
 usb_request_status_t usb_vendor_request_set_transceiver_mode(
 	usb_endpoint_t* const endpoint,
 	const usb_transfer_stage_t stage);
@@ -52,10 +53,11 @@ usb_request_status_t usb_vendor_request_set_antenna_enable(
 	usb_endpoint_t* const endpoint, const usb_transfer_stage_t stage);
 usb_request_status_t usb_vendor_request_set_freq_explicit(
 	usb_endpoint_t* const endpoint, const usb_transfer_stage_t stage);
+usb_request_status_t usb_vendor_request_set_hw_sync_mode(
+	usb_endpoint_t* const endpoint,	const usb_transfer_stage_t stage);
 
 transceiver_mode_t transceiver_mode(void);
 void set_transceiver_mode(const transceiver_mode_t new_transceiver_mode);
-usb_request_status_t usb_vendor_request_set_transceiver_mode(
-	usb_endpoint_t* const endpoint,	const usb_transfer_stage_t stage);
+void start_streaming_on_hw_sync();
 
 #endif/*__USB_API_TRANSCEIVER_H__*/
diff --git a/host/hackrf-tools/src/hackrf_transfer.c b/host/hackrf-tools/src/hackrf_transfer.c
index f38f7ba9..c08889cd 100644
--- a/host/hackrf-tools/src/hackrf_transfer.c
+++ b/host/hackrf-tools/src/hackrf_transfer.c
@@ -114,6 +114,11 @@ typedef enum {
         TRANSCEIVER_MODE_SS = 3,
 } transceiver_mode_t;
 
+typedef enum {
+	HW_SYNC_MODE_OFF = 0,
+	HW_SYNC_MODE_ON = 1,
+} hw_sync_mode_t;
+
 /* WAVE or RIFF WAVE file format containing IQ 2x8bits data for HackRF compatible with SDR# Wav IQ file */
 typedef struct 
 {
@@ -303,6 +308,8 @@ volatile uint32_t byte_count = 0;
 bool signalsource = false;
 uint32_t amplitude = 0;
 
+bool hw_sync = false;
+
 bool receive = false;
 bool receive_wav = false;
 
@@ -463,6 +470,7 @@ static void usage() {
         printf("\t[-R] # Repeat TX mode (default is off) \n");
 	printf("\t[-b baseband_filter_bw_hz] # Set baseband filter bandwidth in Hz.\n\tPossible values: 1.75/2.5/3.5/5/5.5/6/7/8/9/10/12/14/15/20/24/28MHz, default < sample_rate_hz.\n" );
 	printf("\t[-C ppm] # Set Internal crystal clock error in ppm.\n");
+	printf("\t[-H] # Synchronise USB transfer using GPIO pins.\n");
 }
 
 static hackrf_device* device = NULL;
@@ -506,11 +514,14 @@ int main(int argc, char** argv) {
 	float time_diff;
 	unsigned int lna_gain=8, vga_gain=20, txvga_gain=0;
   
-	while( (opt = getopt(argc, argv, "wr:t:f:i:o:m:a:p:s:n:b:l:g:x:c:d:C:R")) != EOF )
+	while( (opt = getopt(argc, argv, "Hwr:t:f:i:o:m:a:p:s:n:b:l:g:x:c:d:C:R")) != EOF )
 	{
 		result = HACKRF_SUCCESS;
 		switch( opt ) 
 		{
+		case 'H':
+			hw_sync = true;
+			break;
 		case 'w':
 			receive_wav = true;
 			break;
@@ -917,6 +928,15 @@ int main(int argc, char** argv) {
 		return EXIT_FAILURE;
 	}
 
+	fprintf(stderr, "call hackrf_set_hw_sync_mode(%d)\n",
+			hw_sync);
+	result = hackrf_set_hw_sync_mode(device, hw_sync ? HW_SYNC_MODE_ON : HW_SYNC_MODE_OFF);
+	if( result != HACKRF_SUCCESS ) {
+		fprintf(stderr, "hackrf_set_hw_sync_mode() failed: %s (%d)\n", hackrf_error_name(result), result);
+		usage();
+		return EXIT_FAILURE;
+	}
+
 	if( transceiver_mode == TRANSCEIVER_MODE_RX ) {
 		result = hackrf_set_vga_gain(device, vga_gain);
 		result |= hackrf_set_lna_gain(device, lna_gain);
diff --git a/host/libhackrf/src/hackrf.c b/host/libhackrf/src/hackrf.c
index 3b57a5a6..59b7eee3 100644
--- a/host/libhackrf/src/hackrf.c
+++ b/host/libhackrf/src/hackrf.c
@@ -71,6 +71,7 @@ typedef enum {
 	HACKRF_VENDOR_REQUEST_INIT_SWEEP = 26,
 	HACKRF_VENDOR_REQUEST_OPERACAKE_GET_BOARDS = 27,
 	HACKRF_VENDOR_REQUEST_OPERACAKE_SET_PORTS = 28,
+	HACKRF_VENDOR_REQUEST_SET_HW_SYNC_MODE = 29,
 } hackrf_vendor_request;
 
 typedef enum {
@@ -86,6 +87,11 @@ typedef enum {
 	TRANSCEIVER_MODE_CPLD_UPDATE = 4,
 } hackrf_transceiver_mode;
 
+typedef enum {
+	HACKRF_HW_SYNC_MODE_OFF = 0,
+	HACKRF_HW_SYNC_MODE_ON = 1,
+} hackrf_hw_sync_mode;
+
 struct hackrf_device {
 	libusb_device_handle* usb_device;
 	struct libusb_transfer** transfers;
@@ -390,7 +396,7 @@ hackrf_device_list_t* ADDCALL hackrf_device_list()
 					serial_number_length = libusb_get_string_descriptor_ascii(usb_device, serial_descriptor_index, (unsigned char*)serial_number, sizeof(serial_number));
 					if( serial_number_length == 32 ) {
 						serial_number[32] = 0;
-						list->serial_numbers[idx] = strdup(serial_number);
+						list->serial_numbers[idx] = strndup(serial_number, serial_number_length);
 					}
 					
 					libusb_close(usb_device);
@@ -1553,6 +1559,26 @@ int ADDCALL hackrf_close(hackrf_device* device)
 	return result1;
 }
 
+int ADDCALL hackrf_set_hw_sync_mode(hackrf_device* device, const uint8_t value) {
+	int result = libusb_control_transfer(
+		device->usb_device,
+ 		LIBUSB_ENDPOINT_OUT | LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_RECIPIENT_DEVICE,
+		HACKRF_VENDOR_REQUEST_SET_HW_SYNC_MODE,
+		value,
+		0,
+		NULL,
+		0,
+		0
+	);
+
+	if( result != 0 )
+	{
+		return HACKRF_ERROR_LIBUSB;
+	} else {
+		return HACKRF_SUCCESS;
+	}
+}
+
 const char* ADDCALL hackrf_error_name(enum hackrf_error errcode)
 {
 	switch(errcode)
diff --git a/host/libhackrf/src/hackrf.h b/host/libhackrf/src/hackrf.h
index 584dd292..296be3d8 100644
--- a/host/libhackrf/src/hackrf.h
+++ b/host/libhackrf/src/hackrf.h
@@ -198,6 +198,9 @@ extern ADDAPI int ADDCALL hackrf_set_txvga_gain(hackrf_device* device, uint32_t
 /* antenna port power control */
 extern ADDAPI int ADDCALL hackrf_set_antenna_enable(hackrf_device* device, const uint8_t value);
 
+/* set hardware sync mode  */
+extern ADDAPI int ADDCALL hackrf_set_hw_sync_mode(hackrf_device* device, const uint8_t value);
+
 extern ADDAPI const char* ADDCALL hackrf_error_name(enum hackrf_error errcode);
 extern ADDAPI const char* ADDCALL hackrf_board_id_name(enum hackrf_board_id board_id);
 extern ADDAPI const char* ADDCALL hackrf_usb_board_id_name(enum hackrf_usb_board_id usb_board_id);