diff --git a/firmware/common/hackrf_core.h b/firmware/common/hackrf_core.h
index 912fa991..c3a47b69 100644
--- a/firmware/common/hackrf_core.h
+++ b/firmware/common/hackrf_core.h
@@ -256,7 +256,8 @@ typedef enum {
 	TRANSCEIVER_MODE_RX = 1,
 	TRANSCEIVER_MODE_TX = 2,
 	TRANSCEIVER_MODE_SS = 3,
-	TRANSCEIVER_MODE_CPLD_UPDATE = 4
+	TRANSCEIVER_MODE_CPLD_UPDATE = 4,
+	TRANSCEIVER_MODE_RX_SWEEP = 5,
 } transceiver_mode_t;
 
 typedef enum {
diff --git a/firmware/hackrf_usb/hackrf_usb.c b/firmware/hackrf_usb/hackrf_usb.c
index 364677ca..f468fc1d 100644
--- a/firmware/hackrf_usb/hackrf_usb.c
+++ b/firmware/hackrf_usb/hackrf_usb.c
@@ -252,46 +252,22 @@ int main(void) {
 	}
 	operacake_init(operacake_allow_gpio);
 
-	unsigned int phase = 0;
-	usb_bulk_buffer_offset = 0;
-
 	while(true) {
-		// Check whether we need to initiate a CPLD update
-		if (start_cpld_update)
-			cpld_update();
-
-		// Check whether we need to initiate sweep mode
-		if (start_sweep_mode) {
-			start_sweep_mode = false;
+		switch (transceiver_mode()) {
+		case TRANSCEIVER_MODE_RX:
+			rx_mode();
+			break;
+		case TRANSCEIVER_MODE_TX:
+			tx_mode();
+			break;
+		case TRANSCEIVER_MODE_RX_SWEEP:
 			sweep_mode();
-		}
-
-		// Set up IN transfer of buffer 0.
-		if ( usb_bulk_buffer_offset >= 16384
-		     && phase == 1
-		     && transceiver_mode() != TRANSCEIVER_MODE_OFF) {
-			usb_transfer_schedule_block(
-				(transceiver_mode() == TRANSCEIVER_MODE_RX)
-				? &usb_endpoint_bulk_in : &usb_endpoint_bulk_out,
-				&usb_bulk_buffer[0x0000],
-				0x4000,
-				NULL, NULL
-				);
-			phase = 0;
-		}
-
-		// Set up IN transfer of buffer 1.
-		if ( usb_bulk_buffer_offset < 16384
-		     && phase == 0
-		     && transceiver_mode() != TRANSCEIVER_MODE_OFF) {
-			usb_transfer_schedule_block(
-				(transceiver_mode() == TRANSCEIVER_MODE_RX)
-				? &usb_endpoint_bulk_in : &usb_endpoint_bulk_out,
-				&usb_bulk_buffer[0x4000],
-				0x4000,
-				NULL, NULL
-			);
-			phase = 1;
+			break;
+		case TRANSCEIVER_MODE_CPLD_UPDATE:
+			cpld_update();
+			break;
+		default:
+			break;
 		}
 	}
 
diff --git a/firmware/hackrf_usb/usb_api_cpld.c b/firmware/hackrf_usb/usb_api_cpld.c
index fc5ab51f..e6fa3784 100644
--- a/firmware/hackrf_usb/usb_api_cpld.c
+++ b/firmware/hackrf_usb/usb_api_cpld.c
@@ -33,7 +33,6 @@
 #include <stdint.h>
 #include <stdbool.h>
 
-volatile bool start_cpld_update = false;
 uint8_t cpld_xsvf_buffer[512];
 volatile bool cpld_wait = false;
 
diff --git a/firmware/hackrf_usb/usb_api_cpld.h b/firmware/hackrf_usb/usb_api_cpld.h
index a097c6a8..5b82eca5 100644
--- a/firmware/hackrf_usb/usb_api_cpld.h
+++ b/firmware/hackrf_usb/usb_api_cpld.h
@@ -28,8 +28,6 @@
 #include <usb_type.h>
 #include <usb_request.h>
 
-extern volatile bool start_cpld_update;
-
 void cpld_update(void);
 
 usb_request_status_t usb_vendor_request_cpld_checksum(
diff --git a/firmware/hackrf_usb/usb_api_sweep.c b/firmware/hackrf_usb/usb_api_sweep.c
index 5c9b5efa..a664c388 100644
--- a/firmware/hackrf_usb/usb_api_sweep.c
+++ b/firmware/hackrf_usb/usb_api_sweep.c
@@ -27,6 +27,7 @@
 #include "usb_bulk_buffer.h"
 #include "tuning.h"
 #include "usb_endpoint.h"
+#include "streaming.h"
 
 #define MIN(x,y)       ((x)<(y)?(x):(y))
 #define MAX(x,y)       ((x)>(y)?(x):(y))
@@ -34,7 +35,6 @@
 #define MAX_RANGES 10
 #define THROWAWAY_BUFFERS 2
 
-volatile bool start_sweep_mode = false;
 static uint64_t sweep_freq;
 static uint16_t frequencies[MAX_RANGES * 2];
 static unsigned char data[9 + MAX_RANGES * 2 * sizeof(frequencies[0])];
@@ -44,6 +44,7 @@ static uint32_t step_width = 0;
 static uint32_t offset = 0;
 static enum sweep_style style = LINEAR;
 
+/* Do this before starting sweep mode with set_transceiver_mode(). */
 usb_request_status_t usb_vendor_request_init_sweep(
 		usb_endpoint_t* const endpoint, const usb_transfer_stage_t stage)
 {
@@ -78,7 +79,6 @@ usb_request_status_t usb_vendor_request_init_sweep(
 		}
 		sweep_freq = (uint64_t)frequencies[0] * FREQ_GRANULARITY;
 		set_freq(sweep_freq + offset);
-		start_sweep_mode = true;
 		usb_transfer_schedule_ack(endpoint->in);
 	}
 	return USB_REQUEST_STATUS_OK;
@@ -93,7 +93,9 @@ void sweep_mode(void) {
 	uint8_t *buffer;
 	bool transfer = false;
 
-	while(transceiver_mode() != TRANSCEIVER_MODE_OFF) {
+	baseband_streaming_enable(&sgpio_config);
+
+	while (TRANSCEIVER_MODE_RX_SWEEP == transceiver_mode()) {
 		// Set up IN transfer of buffer 0.
 		if ( usb_bulk_buffer_offset >= 16384 && phase == 1) {
 			transfer = true;
diff --git a/firmware/hackrf_usb/usb_api_sweep.h b/firmware/hackrf_usb/usb_api_sweep.h
index 20c27859..11ba4395 100644
--- a/firmware/hackrf_usb/usb_api_sweep.h
+++ b/firmware/hackrf_usb/usb_api_sweep.h
@@ -26,8 +26,6 @@
 #include <usb_type.h>
 #include <usb_request.h>
 
-extern volatile bool start_sweep_mode;
-
 enum sweep_style {
 	LINEAR = 0,
 	INTERLEAVED = 1,
diff --git a/firmware/hackrf_usb/usb_api_transceiver.c b/firmware/hackrf_usb/usb_api_transceiver.c
index 90f50810..a113f2e9 100644
--- a/firmware/hackrf_usb/usb_api_transceiver.c
+++ b/firmware/hackrf_usb/usb_api_transceiver.c
@@ -36,8 +36,10 @@
 #include <usb_queue.h>
 
 #include <stddef.h>
+#include <string.h>
 
 #include "usb_endpoint.h"
+#include "usb_api_sweep.h"
 
 typedef struct {
 	uint32_t freq_mhz;
@@ -251,17 +253,22 @@ void set_transceiver_mode(const transceiver_mode_t new_transceiver_mode) {
 
 	_transceiver_mode = new_transceiver_mode;
 	
-	if( _transceiver_mode == TRANSCEIVER_MODE_RX ) {
+	switch (_transceiver_mode) {
+	case TRANSCEIVER_MODE_RX_SWEEP:
+	case TRANSCEIVER_MODE_RX:
 		led_off(LED3);
 		led_on(LED2);
 		rf_path_set_direction(&rf_path, RF_PATH_DIRECTION_RX);
 		usb_bulk_buffer_tx = false;
-	} else if (_transceiver_mode == TRANSCEIVER_MODE_TX) {
+		break;
+	case TRANSCEIVER_MODE_TX:
 		led_off(LED2);
 		led_on(LED3);
 		rf_path_set_direction(&rf_path, RF_PATH_DIRECTION_TX);
 		usb_bulk_buffer_tx = true;
-	} else {
+		break;
+	case TRANSCEIVER_MODE_OFF:
+	default:
 		led_off(LED2);
 		led_off(LED3);
 		rf_path_set_direction(&rf_path, RF_PATH_DIRECTION_OFF);
@@ -274,7 +281,7 @@ void set_transceiver_mode(const transceiver_mode_t new_transceiver_mode) {
 
         hw_sync_enable(_hw_sync_mode);
 
-		baseband_streaming_enable(&sgpio_config);
+		usb_bulk_buffer_offset = 0;
 	}
 }
 
@@ -287,11 +294,9 @@ usb_request_status_t usb_vendor_request_set_transceiver_mode(
 		case TRANSCEIVER_MODE_OFF:
 		case TRANSCEIVER_MODE_RX:
 		case TRANSCEIVER_MODE_TX:
-			set_transceiver_mode(endpoint->setup.value);
-			usb_transfer_schedule_ack(endpoint->in);
-			return USB_REQUEST_STATUS_OK;
+		case TRANSCEIVER_MODE_RX_SWEEP:
 		case TRANSCEIVER_MODE_CPLD_UPDATE:
-			start_cpld_update = true;
+			set_transceiver_mode(endpoint->setup.value);
 			usb_transfer_schedule_ack(endpoint->in);
 			return USB_REQUEST_STATUS_OK;
 		default:
@@ -314,3 +319,70 @@ usb_request_status_t usb_vendor_request_set_hw_sync_mode(
 		return USB_REQUEST_STATUS_OK;
 	}
 }
+
+void rx_mode(void) {
+	unsigned int phase = 1;
+
+	baseband_streaming_enable(&sgpio_config);
+
+	while (TRANSCEIVER_MODE_RX == _transceiver_mode) {
+		// Set up IN transfer of buffer 0.
+		if (16384 <= usb_bulk_buffer_offset && 1 == phase) {
+			usb_transfer_schedule_block(
+				&usb_endpoint_bulk_in,
+				&usb_bulk_buffer[0x0000],
+				0x4000,
+				NULL, NULL
+				);
+			phase = 0;
+		}
+		// Set up IN transfer of buffer 1.
+		if (16384 > usb_bulk_buffer_offset && 0 == phase) {
+			usb_transfer_schedule_block(
+				&usb_endpoint_bulk_in,
+				&usb_bulk_buffer[0x4000],
+				0x4000,
+				NULL, NULL
+				);
+			phase = 1;
+		}
+	}
+}
+
+void tx_mode(void) {
+	unsigned int phase = 1;
+
+	memset(&usb_bulk_buffer[0x0000], 0, 0x8000);
+	// Set up OUT transfer of buffer 1.
+	usb_transfer_schedule_block(
+		&usb_endpoint_bulk_out,
+		&usb_bulk_buffer[0x4000],
+		0x4000,
+		NULL, NULL
+		);
+	// Start transmitting zeros while the host fills buffer 1.
+	baseband_streaming_enable(&sgpio_config);
+
+	while (TRANSCEIVER_MODE_TX == _transceiver_mode) {
+		// Set up OUT transfer of buffer 0.
+		if (16384 <= usb_bulk_buffer_offset && 1 == phase) {
+			usb_transfer_schedule_block(
+				&usb_endpoint_bulk_out,
+				&usb_bulk_buffer[0x0000],
+				0x4000,
+				NULL, NULL
+				);
+			phase = 0;
+		}
+		// Set up OUT transfer of buffer 1.
+		if (16384 > usb_bulk_buffer_offset && 0 == phase) {
+			usb_transfer_schedule_block(
+				&usb_endpoint_bulk_out,
+				&usb_bulk_buffer[0x4000],
+				0x4000,
+				NULL, NULL
+				);
+			phase = 1;
+		}
+	}
+}
diff --git a/firmware/hackrf_usb/usb_api_transceiver.h b/firmware/hackrf_usb/usb_api_transceiver.h
index eb4a5c35..968bc4ed 100644
--- a/firmware/hackrf_usb/usb_api_transceiver.h
+++ b/firmware/hackrf_usb/usb_api_transceiver.h
@@ -59,5 +59,7 @@ usb_request_status_t usb_vendor_request_set_hw_sync_mode(
 transceiver_mode_t transceiver_mode(void);
 void set_transceiver_mode(const transceiver_mode_t new_transceiver_mode);
 void start_streaming_on_hw_sync();
+void rx_mode(void);
+void tx_mode(void);
 
 #endif/*__USB_API_TRANSCEIVER_H__*/
diff --git a/host/hackrf-tools/src/hackrf_sweep.c b/host/hackrf-tools/src/hackrf_sweep.c
index 3d4fd043..4ab3e72f 100644
--- a/host/hackrf-tools/src/hackrf_sweep.c
+++ b/host/hackrf-tools/src/hackrf_sweep.c
@@ -664,13 +664,6 @@ int main(int argc, char** argv) {
 		ifftwPlan = fftwf_plan_dft_1d(fftSize * step_count, ifftwIn, ifftwOut, FFTW_BACKWARD, FFTW_MEASURE);
 	}
 
-	result |= hackrf_start_rx(device, rx_callback, NULL);
-	if (result != HACKRF_SUCCESS) {
-		fprintf(stderr, "hackrf_start_rx() failed: %s (%d)\n", hackrf_error_name(result), result);
-		usage();
-		return EXIT_FAILURE;
-	}
-
 	result = hackrf_init_sweep(device, frequencies, num_ranges, num_samples * 2,
 			TUNE_STEP * FREQ_ONE_MHZ, OFFSET, INTERLEAVED);
 	if( result != HACKRF_SUCCESS ) {
@@ -679,6 +672,13 @@ int main(int argc, char** argv) {
 		return EXIT_FAILURE;
 	}
 
+	result |= hackrf_start_rx_sweep(device, rx_callback, NULL);
+	if (result != HACKRF_SUCCESS) {
+		fprintf(stderr, "hackrf_start_rx_sweep() failed: %s (%d)\n", hackrf_error_name(result), result);
+		usage();
+		return EXIT_FAILURE;
+	}
+
 	if (amp) {
 		fprintf(stderr, "call hackrf_set_amp_enable(%u)\n", amp_enable);
 		result = hackrf_set_amp_enable(device, (uint8_t)amp_enable);
diff --git a/host/libhackrf/src/hackrf.c b/host/libhackrf/src/hackrf.c
index 12c8bcc2..bc1d5fe8 100644
--- a/host/libhackrf/src/hackrf.c
+++ b/host/libhackrf/src/hackrf.c
@@ -96,6 +96,7 @@ typedef enum {
 	HACKRF_TRANSCEIVER_MODE_TRANSMIT = 2,
 	HACKRF_TRANSCEIVER_MODE_SS = 3,
 	TRANSCEIVER_MODE_CPLD_UPDATE = 4,
+	TRANSCEIVER_MODE_RX_SWEEP = 5,
 } hackrf_transceiver_mode;
 
 typedef enum {
@@ -215,6 +216,8 @@ static int allocate_transfers(hackrf_device* const device)
 			return HACKRF_ERROR_NO_MEM;
 		}
 
+		memset(device->buffer, 0, TRANSFER_COUNT * TRANSFER_BUFFER_SIZE);
+
 		for(transfer_index=0; transfer_index<TRANSFER_COUNT; transfer_index++)
 		{
 			device->transfers[transfer_index] = libusb_alloc_transfer(0);
@@ -2162,6 +2165,20 @@ int ADDCALL hackrf_set_ui_enable(hackrf_device* device, const uint8_t value)
 	}
 }
 
+int ADDCALL hackrf_start_rx_sweep(hackrf_device* device, hackrf_sample_block_cb_fn callback, void* rx_ctx)
+{
+	USB_API_REQUIRED(device, 0x0104)
+	int result;
+	const uint8_t endpoint_address = LIBUSB_ENDPOINT_IN | 1;
+	result = hackrf_set_transceiver_mode(device, TRANSCEIVER_MODE_RX_SWEEP);
+	if (HACKRF_SUCCESS == result)
+	{
+		device->rx_ctx = rx_ctx;
+		result = create_transfer_thread(device, endpoint_address, callback);
+	}
+	return result;
+}
+
 #ifdef __cplusplus
 } // __cplusplus defined.
 #endif
diff --git a/host/libhackrf/src/hackrf.h b/host/libhackrf/src/hackrf.h
index 9cdf2c48..2cbac532 100644
--- a/host/libhackrf/src/hackrf.h
+++ b/host/libhackrf/src/hackrf.h
@@ -259,6 +259,7 @@ extern ADDAPI int ADDCALL hackrf_cpld_checksum(hackrf_device* device,
 #endif /* HACKRF_ISSUE_609_IS_FIXED */
 
 extern ADDAPI int ADDCALL hackrf_set_ui_enable(hackrf_device* device, const uint8_t value);
+extern ADDAPI int ADDCALL hackrf_start_rx_sweep(hackrf_device* device, hackrf_sample_block_cb_fn callback, void* rx_ctx);
 
 #ifdef __cplusplus
 } // __cplusplus defined.