sdr/sx: implement timed transmission

The test generates a continuous carrier signal, offset by 20 kHz from
the center frequency. The generated carrier must be clean when
received by another device.

impl/CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required (VERSION 3.20)
 project (hamnet70 VERSION 0.1 LANGUAGES C)
 
 set(CMAKE_C_STANDARD 99)
-set(CMAKE_C_FLAGS "-Wall -pedantic -Wextra -DDEBUG_LIQUID")
+set(CMAKE_C_FLAGS "-Wall -pedantic -Wextra -DDEBUG_LIQUID -fsanitize=address")
 
 include_directories(src)
 
@@ -55,8 +55,8 @@ set(sources
 	src/layer2/ham64.h
 	src/layer2/connection.c
 	src/layer2/connection.h
-	src/sdr/sdr.c
-	src/sdr/sdr.h
+	src/sdr/sdr_sxceiver.c
+	src/sdr/sdr_sxceiver.h
 )
 
 include_directories(
@@ -75,7 +75,7 @@ target_link_libraries(
 	rt
 	fftw3f
 	fec
-	hackrf
+	SoapySDR
 )
 
 add_subdirectory(test)

impl/src/main.c

@@ -35,7 +35,7 @@
 
 #include "layer2/tundev.h"
 
-#include "sdr/sdr.h"
+#include "sdr/sdr_sxceiver.h"
 
 #include "config.h"
 
@@ -50,6 +50,8 @@
 static int  m_tunfd = -1;
 static bool m_running = true;
 
+static double m_tstart = 0.0;
+
 static double next_tx_switch_time = 0.0;
 
 static rx_stats_t m_rx_stats;
@@ -149,14 +151,8 @@ void cb_rx(rx_evt_t evt, const struct layer1_rx_s *rx, uint8_t *packet_data, siz
 
 static result_t transmit(sdr_ctx_t *sdr, const float complex *samples, size_t len)
 {
-	size_t to_transmit_rf = len * SDR_OVERSAMPLING;
-	float complex *rf_samples = malloc(sizeof(*rf_samples) * to_transmit_rf);
-
-	RESULT_CHECK(sdr_baseband_to_rf(sdr, samples, len, rf_samples, &to_transmit_rf));
-
-	result_t result = sdr_transmit(sdr, rf_samples, to_transmit_rf, 100000);
-
-	free(rf_samples);
+	int64_t tx_time_ns = (int64_t)((get_hires_time() - m_tstart + 0.1) * 1e9);
+	result_t result = sdr_transmit(sdr, samples, len, tx_time_ns, 100000);
 
 	fprintf(stderr, "t");
 	return result;
@@ -230,10 +226,11 @@ int main(int argc, char **argv)
 
 	// start in TX mode to work around SoapyHackRF not setting the correct frequency.
 	RESULT_CHECK(sdr_start_tx(&sdr, 1));
+	m_tstart = get_hires_time();
 
 	unsigned rx_retries = 0;
 
-	double old = get_hires_time();
+	double old = m_tstart;
 	size_t total_samples = 0;
 	double next_stats_print_time = old + 0.5;
 
@@ -256,7 +253,7 @@ int main(int argc, char **argv)
 				// there is a packet to be (re)transmitted.
 
 				// check free buffer space (50 ms required corresponding to 5000 baseband symbols)
-				size_t buffer_free_space_samples = sdr_get_tx_buffer_free_space(&sdr);
+				size_t buffer_free_space_samples = 1000000; // FIXME! sdr_get_tx_buffer_free_space(&sdr);
 
 				LOG(LVL_DEBUG, "TX buffer free: %zu", buffer_free_space_samples);
 
@@ -318,7 +315,6 @@ int main(int argc, char **argv)
 				on_air = true;
 			} else if(on_air) { // TX on, but no more bursts to send
 				LOG(LVL_INFO, "TX -> RX");
-				RESULT_CHECK(sdr_flush_tx_buffer(&sdr));
 				RESULT_CHECK(layer1_rx_reset(&rx));
 
 				RESULT_CHECK(sdr_stop_tx(&sdr));
@@ -343,7 +339,7 @@ int main(int argc, char **argv)
 			size_t n_rf_samples = CHUNKSIZE_RF;
 			size_t n_bb_samples = CHUNKSIZE_BB;
 
-			if(sdr_receive(&sdr, rf_samples, &n_rf_samples, 100000, SDR_OVERSAMPLING) != OK) {
+			if(sdr_receive(&sdr, bb_samples, &n_bb_samples, 100000) != OK) {
 				rx_retries++;
 				LOG(LVL_INFO, "sdr_receive() failed %d times.", rx_retries);
 				if(rx_retries >= 3) {
@@ -382,8 +378,6 @@ int main(int argc, char **argv)
 
 			fprintf(stderr, "r");
 
-			RESULT_CHECK(sdr_rf_to_baseband(&sdr, rf_samples, n_rf_samples, bb_samples, &n_bb_samples));
-
 			RESULT_CHECK(layer1_rx_process(&rx, bb_samples, n_bb_samples));
 		} else {
 			rx_retries = 0;

impl/src/sdr/sdr_sxceiver.c

@@ -0,0 +1,330 @@
+#include <SoapySDR/Device.h>
+#include <SoapySDR/Formats.h>
+#include <SoapySDR/Logger.h>
+#include <liquid/liquid.h>
+#include <stdio.h> //printf
+#include <stdlib.h> //free
+#include <complex.h>
+#include <math.h>
+#include <string.h>
+
+#include "logger.h"
+
+#include "config.h"
+#include "utils.h"
+#include "results.h"
+
+#include "sdr_sxceiver.h"
+
+void soapy_log_handler(const SoapySDRLogLevel logLevel, const char *message)
+{
+	int level;
+
+	switch(logLevel) {
+		case SOAPY_SDR_CRITICAL:
+		case SOAPY_SDR_FATAL:
+			level = LVL_FATAL;
+			break;
+
+		case SOAPY_SDR_ERROR:
+			level = LVL_ERR;
+			break;
+
+		case SOAPY_SDR_WARNING:
+			level = LVL_WARN;
+			break;
+
+		case SOAPY_SDR_INFO:
+			level = LVL_INFO;
+			break;
+
+		case SOAPY_SDR_DEBUG:
+			level = LVL_DEBUG;
+			break;
+
+		default:
+			level = LVL_DUMP;
+			break;
+	}
+
+	LOG(level, "soapy [%d]: %s", logLevel, message);
+}
+
+static void close_streams(sdr_ctx_t *ctx)
+{
+	if(ctx->rx_stream) {
+		SoapySDRDevice_deactivateStream(ctx->sdr, ctx->rx_stream, 0, 0);
+		SoapySDRDevice_closeStream(ctx->sdr, ctx->rx_stream);
+	}
+
+	if(ctx->tx_stream) {
+		SoapySDRDevice_deactivateStream(ctx->sdr, ctx->tx_stream, 0, 0);
+		SoapySDRDevice_closeStream(ctx->sdr, ctx->tx_stream);
+	}
+}
+
+
+result_t sdr_init(sdr_ctx_t *ctx)
+{
+	size_t length;
+
+	ctx->sdr = NULL;
+	ctx->tx_stream = NULL;
+	ctx->rx_stream = NULL;
+
+	ctx->tx_nco = nco_crcf_create(LIQUID_NCO);
+	ctx->rx_nco = nco_crcf_create(LIQUID_NCO);
+
+	nco_crcf_set_frequency(ctx->tx_nco, 2 * M_PI * SDR_TX_IF_SHIFT / SDR_TX_SAMPLING_RATE);
+	nco_crcf_set_frequency(ctx->rx_nco, 2 * M_PI * SDR_RX_IF_SHIFT / SDR_RX_SAMPLING_RATE);
+
+	// set up logging
+	SoapySDR_registerLogHandler(soapy_log_handler);
+	//SoapySDR_setLogLevel(SOAPY_SDR_DEBUG);
+
+	//enumerate devices
+	SoapySDRKwargs *results = SoapySDRDevice_enumerate(NULL, &length);
+	for (size_t i = 0; i < length; i++)
+	{
+		LOG(LVL_INFO, "Found device #%d:", (int)i);
+		for (size_t j = 0; j < results[i].size; j++)
+		{
+			LOG(LVL_INFO, "- %s=%s", results[i].keys[j], results[i].vals[j]);
+		}
+		LOG(LVL_ERR, "");
+	}
+	SoapySDRKwargsList_clear(results, length);
+
+	//create device instance
+	//args can be user defined or from the enumeration result
+	SoapySDRKwargs args;
+	memset(&args, 0, sizeof(args));
+	SoapySDRKwargs_set(&args, "driver", "sx");
+	ctx->sdr = SoapySDRDevice_make(&args);
+	SoapySDRKwargs_clear(&args);
+
+	if (ctx->sdr == NULL)
+	{
+		LOG(LVL_ERR, "SoapySDRDevice_make fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	//query device info
+	SoapySDRRange *ranges;
+	char** names = SoapySDRDevice_listAntennas(ctx->sdr, SOAPY_SDR_RX, 0, &length);
+	LOG(LVL_INFO, "Rx antennas: ");
+	for (size_t i = 0; i < length; i++) LOG(LVL_INFO, "%s, ", names[i]);
+	LOG(LVL_INFO, "");
+	SoapySDRStrings_clear(&names, length);
+
+	names = SoapySDRDevice_listGains(ctx->sdr, SOAPY_SDR_RX, 0, &length);
+	LOG(LVL_INFO, "Rx gains: ");
+	for (size_t i = 0; i < length; i++) {
+		SoapySDRRange range = SoapySDRDevice_getGainRange(ctx->sdr, SOAPY_SDR_RX, i);
+		LOG(LVL_INFO, "%s [%.3lf .. %.3lf / %.3lf], ", names[i], range.minimum, range.maximum, range.step);
+	}
+	LOG(LVL_INFO, "");
+	SoapySDRStrings_clear(&names, length);
+
+	ranges = SoapySDRDevice_getFrequencyRange(ctx->sdr, SOAPY_SDR_RX, 0, &length);
+	LOG(LVL_INFO, "Rx freq ranges: ");
+	for (size_t i = 0; i < length; i++) LOG(LVL_INFO, "[%g Hz -> %g Hz], ", ranges[i].minimum, ranges[i].maximum);
+	LOG(LVL_INFO, "");
+	free(ranges);
+
+	names = SoapySDRDevice_listAntennas(ctx->sdr, SOAPY_SDR_TX, 0, &length);
+	LOG(LVL_INFO, "Tx antennas: ");
+	for (size_t i = 0; i < length; i++) LOG(LVL_INFO, "%s, ", names[i]);
+	LOG(LVL_INFO, "");
+	SoapySDRStrings_clear(&names, length);
+
+	names = SoapySDRDevice_listGains(ctx->sdr, SOAPY_SDR_TX, 0, &length);
+	LOG(LVL_INFO, "Tx gains: ");
+	for (size_t i = 0; i < length; i++) {
+		SoapySDRRange range = SoapySDRDevice_getGainRange(ctx->sdr, SOAPY_SDR_TX, i);
+		LOG(LVL_INFO, "%s [%.3lf .. %.3lf / %.3lf], ", names[i], range.minimum, range.maximum, range.step);
+	}
+	LOG(LVL_INFO, "");
+	SoapySDRStrings_clear(&names, length);
+
+	ranges = SoapySDRDevice_getFrequencyRange(ctx->sdr, SOAPY_SDR_TX, 0, &length);
+	LOG(LVL_INFO, "Tx freq ranges: ");
+	for (size_t i = 0; i < length; i++) LOG(LVL_INFO, "[%g Hz -> %g Hz], ", ranges[i].minimum, ranges[i].maximum);
+	LOG(LVL_INFO, "");
+	free(ranges);
+
+	//setup streams
+	ctx->rx_stream = SoapySDRDevice_setupStream(ctx->sdr, SOAPY_SDR_RX, SOAPY_SDR_CF32, NULL, 0, NULL);
+
+	if(ctx->rx_stream == NULL) {
+		LOG(LVL_ERR, "setupStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	ctx->tx_stream = SoapySDRDevice_setupStream(ctx->sdr, SOAPY_SDR_TX, SOAPY_SDR_CF32, NULL, 0, NULL);
+
+	if(ctx->tx_stream == NULL) {
+		LOG(LVL_ERR, "setupStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	//apply settings
+	if (SoapySDRDevice_setSampleRate(ctx->sdr, SOAPY_SDR_RX, 0, SDR_RX_SAMPLING_RATE) != 0) {
+		LOG(LVL_ERR, "setSampleRate fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+	if (SoapySDRDevice_setFrequency(ctx->sdr, SOAPY_SDR_RX, 0, SDR_RX_FREQ - SDR_RX_IF_SHIFT, NULL) != 0) {
+		LOG(LVL_ERR, "setFrequency fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	if (SoapySDRDevice_setSampleRate(ctx->sdr, SOAPY_SDR_TX, 0, SDR_TX_SAMPLING_RATE) != 0) {
+		LOG(LVL_ERR, "setSampleRate fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+	if (SoapySDRDevice_setFrequency(ctx->sdr, SOAPY_SDR_TX, 0, SDR_TX_FREQ, NULL) != 0) {
+		LOG(LVL_ERR, "setFrequency fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+#if 0
+	// PA always on
+	if (SoapySDRDevice_writeSetting(ctx->sdr, "PA", "ON") != 0) {
+		LOG(LVL_ERR, "writeSetting fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+#endif
+
+	// set up and start RX
+
+	// set gains
+	if(SoapySDRDevice_setGainElement(ctx->sdr, SOAPY_SDR_RX, 0, "PGA", SDR_GAIN_RX_PGA) != 0) {
+		LOG(LVL_ERR, "setGainElement fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	if(SoapySDRDevice_setGainElement(ctx->sdr, SOAPY_SDR_RX, 0, "LNA", SDR_GAIN_RX_LNA) != 0) {
+		LOG(LVL_ERR, "setGainElement fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	if(SoapySDRDevice_activateStream(ctx->sdr, ctx->rx_stream, 0, 0, 0) != 0) {
+		LOG(LVL_ERR, "activateStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	// set up and start TX
+
+	// set gain
+	/*if(SoapySDRDevice_setGainElement(ctx->sdr, SOAPY_SDR_TX, 0, "DAC", SDR_GAIN_TX_DAC) != 0) {
+		LOG(LVL_ERR, "setGainElement fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	if(SoapySDRDevice_setGainElement(ctx->sdr, SOAPY_SDR_TX, 0, "MIXER", SDR_GAIN_TX_MIXER) != 0) {
+		LOG(LVL_ERR, "setGainElement fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}*/
+
+	if(SoapySDRDevice_setGain(ctx->sdr, SOAPY_SDR_TX, 0, SDR_GAIN_TX) != 0) {
+		LOG(LVL_ERR, "setGain fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	if(SoapySDRDevice_activateStream(ctx->sdr, ctx->tx_stream, 0, 0, 0) != 0) {
+		LOG(LVL_ERR, "activateStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	return OK;
+}
+
+
+result_t sdr_destroy(sdr_ctx_t *ctx)
+{
+	close_streams(ctx);
+
+	nco_crcf_destroy(ctx->rx_nco);
+	nco_crcf_destroy(ctx->tx_nco);
+
+	if(ctx->sdr) {
+		SoapySDRDevice_unmake(ctx->sdr);
+	}
+
+	return OK;
+}
+
+
+result_t sdr_start_rx(sdr_ctx_t *ctx)
+{
+
+	return OK;
+}
+
+
+result_t sdr_start_tx(sdr_ctx_t *ctx, size_t burst_size)
+{
+
+	return OK;
+}
+
+
+result_t sdr_stop_rx(sdr_ctx_t *ctx)
+{
+	return OK;
+}
+
+
+result_t sdr_stop_tx(sdr_ctx_t *ctx)
+{
+	return OK;
+}
+
+
+result_t sdr_transmit(sdr_ctx_t *ctx, const float complex *samples, size_t nsamples, int64_t time_ns, long timeout_us)
+{
+	if(ctx->tx_stream == NULL) {
+		return ERR_INVALID_STATE;
+	}
+
+	int flags = 0;
+	if(time_ns != 0) {
+		flags |= SOAPY_SDR_HAS_TIME;
+	}
+
+	void *buffs[] = {(void*)(samples)};
+
+	int ret = SoapySDRDevice_writeStream(ctx->sdr, ctx->tx_stream, (const void* const*)buffs, nsamples, &flags, time_ns, timeout_us);
+
+	if(ret <= 0) {
+		LOG(LVL_ERR, "writeStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	} else if(ret != nsamples) {
+		LOG(LVL_WARN, "writeStream() did not transmit all samples: %i/%zu", ret, nsamples);
+	}
+
+	return OK;
+}
+
+
+result_t sdr_receive(sdr_ctx_t *ctx, float complex *samples, size_t *nsamples, long timeout_us)
+{
+	if(ctx->rx_stream == NULL) {
+		return ERR_INVALID_STATE;
+	}
+
+	void *buffs[] = {(void*)samples};
+
+	long long timeNs;
+	int flags;
+	int ret = SoapySDRDevice_readStream(ctx->sdr, ctx->rx_stream, (void* const*)buffs, *nsamples, &flags, &timeNs, timeout_us);
+
+	if(ret <= 0) {
+		LOG(LVL_ERR, "readStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	*nsamples = ret;
+
+	return OK;
+}

impl/src/sdr/sdr_sxceiver.h

@@ -0,0 +1,34 @@
+#ifndef SDR_SDR_H
+#define SDR_SDR_H
+
+#include <complex.h>
+
+#include <SoapySDR/Device.h>
+
+#include <liquid/liquid.h>
+
+#include "results.h"
+
+typedef struct {
+	SoapySDRDevice *sdr;
+
+	SoapySDRStream *rx_stream;
+	SoapySDRStream *tx_stream;
+
+	nco_crcf       tx_nco;
+	nco_crcf       rx_nco;
+} sdr_ctx_t;
+
+result_t sdr_init(sdr_ctx_t *ctx);
+result_t sdr_destroy(sdr_ctx_t *ctx);
+
+result_t sdr_start_rx(sdr_ctx_t *ctx);
+result_t sdr_start_tx(sdr_ctx_t *ctx, size_t burst_size);
+
+result_t sdr_stop_rx(sdr_ctx_t *ctx);
+result_t sdr_stop_tx(sdr_ctx_t *ctx);
+
+result_t sdr_transmit(sdr_ctx_t *ctx, const float complex *samples, size_t nsamples, int64_t time_ns, long timeout_us);
+result_t sdr_receive(sdr_ctx_t *ctx, float complex *samples, size_t *nsamples, long timeout_us);
+
+#endif // SDR_SDR_H

impl/test/CMakeLists.txt

@@ -222,3 +222,24 @@ target_link_libraries(
 	test_interleaver
 	m
 )
+
+#------------------------------------
+
+add_executable(
+	test_sx
+	../src/utils.c
+	../src/utils.h
+	../src/logger.c
+	../src/logger.h
+	test_sx.c
+)
+
+target_link_libraries(
+	test_sx
+	liquid
+	m
+	rt
+	fftw3f
+	fec
+	SoapySDR
+)

impl/test/test_sx.c

@@ -0,0 +1,195 @@
+#include <SoapySDR/Device.h>
+#include <SoapySDR/Formats.h>
+#include <SoapySDR/Logger.h>
+
+#include <string.h>
+#include <math.h>
+
+#include "logger.h"
+#include "config.h"
+#include "results.h"
+#include "utils.h"
+
+void soapy_log_handler(const SoapySDRLogLevel logLevel, const char *message)
+{
+	int level;
+
+	switch(logLevel) {
+		case SOAPY_SDR_CRITICAL:
+		case SOAPY_SDR_FATAL:
+			level = LVL_FATAL;
+			break;
+
+		case SOAPY_SDR_ERROR:
+			level = LVL_ERR;
+			break;
+
+		case SOAPY_SDR_WARNING:
+			level = LVL_WARN;
+			break;
+
+		case SOAPY_SDR_INFO:
+			level = LVL_INFO;
+			break;
+
+		case SOAPY_SDR_DEBUG:
+			level = LVL_DEBUG;
+			break;
+
+		default:
+			level = LVL_DUMP;
+			break;
+	}
+
+	LOG(level, "soapy [%d]: %s", logLevel, message);
+}
+
+
+typedef struct {
+	SoapySDRDevice *sdr;
+
+	SoapySDRStream *rx_stream;
+	SoapySDRStream *tx_stream;
+} sdr_ctx_t;
+
+
+int main(void)
+{
+	sdr_ctx_t ctx;
+
+	logger_init();
+
+	// set up logging
+	SoapySDR_registerLogHandler(soapy_log_handler);
+	SoapySDR_setLogLevel(SOAPY_SDR_DEBUG);
+
+	SoapySDRKwargs args;
+	memset(&args, 0, sizeof(args));
+	SoapySDRKwargs_set(&args, "driver", "sx");
+	ctx.sdr = SoapySDRDevice_make(&args);
+	SoapySDRKwargs_clear(&args);
+
+	if (ctx.sdr == NULL)
+	{
+		LOG(LVL_ERR, "SoapySDRDevice_make fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	//setup streams
+	ctx.rx_stream = SoapySDRDevice_setupStream(ctx.sdr, SOAPY_SDR_RX, SOAPY_SDR_CF32, NULL, 0, NULL);
+
+	if(ctx.rx_stream == NULL) {
+		LOG(LVL_ERR, "setupStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	ctx.tx_stream = SoapySDRDevice_setupStream(ctx.sdr, SOAPY_SDR_TX, SOAPY_SDR_CF32, NULL, 0, NULL);
+
+	if(ctx.tx_stream == NULL) {
+		LOG(LVL_ERR, "setupStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	//apply settings
+	if (SoapySDRDevice_setSampleRate(ctx.sdr, SOAPY_SDR_RX, 0, SDR_RX_SAMPLING_RATE) != 0) {
+		LOG(LVL_ERR, "setSampleRate fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+	if (SoapySDRDevice_setFrequency(ctx.sdr, SOAPY_SDR_RX, 0, SDR_RX_FREQ - SDR_RX_IF_SHIFT, NULL) != 0) {
+		LOG(LVL_ERR, "setFrequency fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	if (SoapySDRDevice_setSampleRate(ctx.sdr, SOAPY_SDR_TX, 0, SDR_TX_SAMPLING_RATE) != 0) {
+		LOG(LVL_ERR, "setSampleRate fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+	if (SoapySDRDevice_setFrequency(ctx.sdr, SOAPY_SDR_TX, 0, SDR_TX_FREQ, NULL) != 0) {
+		LOG(LVL_ERR, "setFrequency fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+	if(SoapySDRDevice_setGain(ctx.sdr, SOAPY_SDR_TX, 0, SDR_GAIN_TX) != 0) {
+		LOG(LVL_ERR, "setGain fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+
+#define BUFSIZE 300000
+
+#if 0
+	if(SoapySDRDevice_activateStream(ctx.sdr, ctx.tx_stream, 0, 0, 0) != 0) {
+		LOG(LVL_ERR, "activateStream fail: %s", SoapySDRDevice_lastError());
+		return ERR_SOAPY;
+	}
+#endif
+
+	float complex samples[BUFSIZE];
+
+	float twopi = 6.283185307f;
+	float offset_hz = 20e3;
+	float fm_osc_freq_hz = 1.0f;
+	float fm_osc_dev_hz = 5e3;
+
+	float fm_dphi = twopi * fm_osc_freq_hz / SDR_TX_SAMPLING_RATE;
+
+	float fm_phi = 0.0f;
+	float phi = 0.0f;
+
+	int64_t timeNs = 0;
+
+	while(true) {
+
+		for(size_t i = 0; i < BUFSIZE; i++) {
+			fm_phi += fm_dphi;
+			if(fm_phi > twopi) {
+				fm_phi -= twopi;
+			}
+
+			float fm_dev_hz = fm_osc_dev_hz * sinf(fm_phi);
+
+			float dphi = twopi * (offset_hz + fm_dev_hz) / SDR_TX_SAMPLING_RATE;
+
+			phi += dphi;
+			if(phi > twopi) {
+				phi -= twopi;
+			}
+			samples[i] = cexpf(I * phi);
+		}
+
+		timeNs += 1000000000LL + 1000000000LL * BUFSIZE / SDR_TX_SAMPLING_RATE;
+
+		if(SoapySDRDevice_activateStream(ctx.sdr, ctx.tx_stream, 0, 0, 0) != 0) {
+			LOG(LVL_ERR, "activateStream fail: %s", SoapySDRDevice_lastError());
+			return ERR_SOAPY;
+		}
+
+		double tstart = get_hires_time();
+
+		int flags = 0;
+		void *buffs[] = {(void*)samples};
+		size_t timeout_us = 100000;
+		int ret = SoapySDRDevice_writeStream(ctx.sdr, ctx.tx_stream, (const void* const*)buffs, BUFSIZE, &flags, timeNs, timeout_us);
+
+		if(ret <= 0) {
+			LOG(LVL_ERR, "writeStream fail: %s", SoapySDRDevice_lastError());
+			return ERR_SOAPY;
+		}
+
+		double tend_write = get_hires_time();
+
+		if(SoapySDRDevice_deactivateStream(ctx.sdr, ctx.tx_stream, 0, 0) != 0) {
+			LOG(LVL_ERR, "deactivateStream fail: %s", SoapySDRDevice_lastError());
+			return ERR_SOAPY;
+		}
+
+		double tend = get_hires_time();
+
+		LOG(LVL_INFO, "write duration: %.3f ms", (tend_write - tstart) * 1000);
+		LOG(LVL_INFO, "total duration: %.3f ms", (tend - tstart) * 1000);
+
+
+		fsleep(1);
+	}
+
+	return OK;
+}