direct sampling mode switching depending on center_frequency

added API function rtlsdr_set_ds_mode(dev, enum rtlsdr_ds_mode, freq_threshold)
added CLI option '-D' to rtl_(fm|power|tcp) for mode and threshold frequency

Signed-off-by: hayati ayguen <[email protected]>

include/rtl-sdr.h

@@ -342,6 +342,25 @@ RTLSDR_API int rtlsdr_set_direct_sampling(rtlsdr_dev_t *dev, int on);
  */
 RTLSDR_API int rtlsdr_get_direct_sampling(rtlsdr_dev_t *dev);
 
+enum rtlsdr_ds_mode {
+	RTLSDR_DS_IQ = 0,	/* I/Q quadrature sampling of tuner output */
+	RTLSDR_DS_I,		/* 1: direct sampling on I branch: usually not connected */
+	RTLSDR_DS_Q,		/* 2: direct sampling on Q branch: HF on rtl-sdr v3 dongle */
+	RTLSDR_DS_I_BELOW,	/* 3: direct sampling on I branch when frequency below 'DS threshold frequency' */
+	RTLSDR_DS_Q_BELOW	/* 4: direct sampling on Q branch when frequency below 'DS threshold frequency' */
+};
+
+/*!
+ * Set direct sampling mode with threshold
+ *
+ * \param dev the device handle given by rtlsdr_open()
+ * \param mode static modes 0 .. 2 as in rtlsdr_set_direct_sampling(). other modes do automatic switching
+ * \param freq_threshold direct sampling is used below this frequency, else quadrature mode through tuner
+ *   set 0 for using default setting per tuner - not fully implemented yet!
+ * \return negative on error, 0 on success
+ */
+RTLSDR_API int rtlsdr_set_ds_mode(rtlsdr_dev_t *dev, enum rtlsdr_ds_mode mode, uint32_t freq_threshold);
+
 /*!
  * Enable or disable offset tuning for zero-IF tuners, which allows to avoid
  * problems caused by the DC offset of the ADCs and 1/f noise.

src/librtlsdr.c

@@ -119,6 +119,8 @@ struct rtlsdr_dev {
 	uint32_t offs_freq; /* Hz */
 	int corr; /* ppm */
 	int gain; /* tenth dB */
+	enum rtlsdr_ds_mode direct_sampling_mode;
+	uint32_t direct_sampling_threshold; /* Hz */
 	struct e4k_state e4k_s;
 	struct r82xx_config r82xx_c;
 	struct r82xx_priv r82xx_p;
@@ -131,6 +133,7 @@ struct rtlsdr_dev {
 
 void rtlsdr_set_gpio_bit(rtlsdr_dev_t *dev, uint8_t gpio, int val);
 static int rtlsdr_set_if_freq(rtlsdr_dev_t *dev, uint32_t freq);
+static int rtlsdr_update_ds(rtlsdr_dev_t *dev, uint32_t freq);
 
 /* generic tuner interface functions, shall be moved to the tuner implementations */
 int e4000_init(void *dev) {
@@ -996,6 +999,9 @@ int rtlsdr_set_center_freq(rtlsdr_dev_t *dev, uint32_t freq)
 	if (!dev || !dev->tuner)
 		return -1;
 
+	if (dev->direct_sampling_mode > RTLSDR_DS_Q)
+		rtlsdr_update_ds(dev, freq);
+
 	if (dev->direct_sampling) {
 		r = rtlsdr_set_if_freq(dev, freq);
 	} else if (dev->tuner && dev->tuner->set_freq) {
@@ -1485,6 +1491,59 @@ int rtlsdr_get_direct_sampling(rtlsdr_dev_t *dev)
 	return dev->direct_sampling;
 }
 
+int rtlsdr_set_ds_mode(rtlsdr_dev_t *dev, enum rtlsdr_ds_mode mode, uint32_t freq_threshold)
+{
+	if (!dev)
+		return -1;
+
+	uint32_t center_freq = rtlsdr_get_center_freq(dev);
+	if ( !center_freq )
+		return -2;
+
+	if (!freq_threshold) {
+		switch(dev->tuner_type) {
+		default:
+		case RTLSDR_TUNER_UNKNOWN:	freq_threshold = 28800000; break; /* no idea!!! */
+		case RTLSDR_TUNER_E4000:	freq_threshold = 50*1000000; break; /* E4K_FLO_MIN_MHZ */
+		case RTLSDR_TUNER_FC0012:	freq_threshold = 28800000; break; /* no idea!!! */
+		case RTLSDR_TUNER_FC0013:	freq_threshold = 28800000; break; /* no idea!!! */
+		case RTLSDR_TUNER_FC2580:	freq_threshold = 28800000; break; /* no idea!!! */
+		case RTLSDR_TUNER_R820T:	freq_threshold = 24000000; break; /* ~ */
+		case RTLSDR_TUNER_R828D:	freq_threshold = 28800000; break; /* no idea!!! */
+		}
+	}
+
+	dev->direct_sampling_mode = mode;
+	dev->direct_sampling_threshold = freq_threshold;
+
+	if (mode <= RTLSDR_DS_Q)
+		rtlsdr_set_direct_sampling(dev, mode);
+
+	return rtlsdr_set_center_freq(dev, center_freq);
+}
+
+static int rtlsdr_update_ds(rtlsdr_dev_t *dev, uint32_t freq)
+{
+	int curr_ds = rtlsdr_get_direct_sampling(dev);
+	if ( curr_ds < 0 )
+		return -1;
+
+	int new_ds = 0;
+	switch (dev->direct_sampling_mode) {
+	default:
+	case RTLSDR_DS_IQ:		break;
+	case RTLSDR_DS_I:		new_ds = 1; break;
+	case RTLSDR_DS_Q:		new_ds = 2; break;
+	case RTLSDR_DS_I_BELOW:	new_ds = (freq < dev->direct_sampling_threshold) ? 1 : 0; break;
+	case RTLSDR_DS_Q_BELOW:	new_ds = (freq < dev->direct_sampling_threshold) ? 2 : 0; break;
+	}
+
+	if ( curr_ds != new_ds )
+		return rtlsdr_set_direct_sampling(dev, new_ds);
+
+	return 0;
+}
+
 int rtlsdr_set_offset_tuning(rtlsdr_dev_t *dev, int on)
 {
 	int r = 0;

src/rtl_fm.c

@@ -209,6 +209,8 @@ void usage(void)
 		"\t[-s sample_rate (default: 24k)]\n"
 		"\t[-d device_index (default: 0)]\n"
 		"\t[-T enable bias-T on GPIO PIN 0 (works for rtl-sdr.com v3 dongles)]\n"
+		"\t[-D direct_sampling_mode (default: 0, 1 = I, 2 = Q, 3 = I below threshold, 4 = Q below threshold)]\n"
+		"\t[-D direct_sampling_threshold_frequency (default: 0 use tuner specific frequency threshold for 3 and 4)]\n"
 		"\t[-g tuner_gain (default: automatic)]\n"
 		"\t[-w tuner_bandwidth (default: automatic. enables offset tuning)]\n"
 		"\t[-l squelch_level (default: 0/off)]\n"
@@ -1166,14 +1168,16 @@ int main(int argc, char **argv)
 	int dev_given = 0;
 	int custom_ppm = 0;
 	int enable_biastee = 0;
+	enum rtlsdr_ds_mode ds_mode = RTLSDR_DS_IQ;
+	uint32_t ds_temp, ds_threshold = 0;
 	int timeConstant = 75; /* default: U.S. 75 uS */
 	int rtlagc = 0;
 	dongle_init(&dongle);
 	demod_init(&demod);
 	output_init(&output);
 	controller_init(&controller);
 
-	while ((opt = getopt(argc, argv, "d:f:g:s:b:l:L:o:t:r:p:E:q:F:A:M:c:h:w:Tv")) != -1) {
+	while ((opt = getopt(argc, argv, "d:f:g:s:b:l:L:o:t:r:p:E:q:F:A:M:c:h:w:D:Tv")) != -1) {
 		switch (opt) {
 		case 'd':
 			dongle.dev_index = verbose_device_search(optarg);
@@ -1289,6 +1293,13 @@ int main(int argc, char **argv)
 		case 'T':
 			enable_biastee = 1;
 			break;
+		case 'D':
+			ds_temp = (uint32_t)( atofs(optarg) + 0.5 );
+			if (ds_temp <= RTLSDR_DS_Q_BELOW)
+				ds_mode = (enum rtlsdr_ds_mode)ds_temp;
+			else
+				ds_threshold = ds_temp;
+			break;
 		case 'v':
 			++verbosity;
 			break;
@@ -1375,6 +1386,9 @@ int main(int argc, char **argv)
 
 	verbose_ppm_set(dongle.dev, dongle.ppm_error);
 
+	/* Set direct sampling with threshold */
+	rtlsdr_set_ds_mode(dongle.dev, ds_mode, ds_threshold);
+
  	verbose_set_bandwidth(dongle.dev, dongle.bandwidth);
 
 	if (verbosity && dongle.bandwidth)

src/rtl_power.c

@@ -137,6 +137,8 @@ void usage(void)
 		"\t[-g tuner_gain (default: automatic)]\n"
 		"\t[-p ppm_error (default: 0)]\n"
 		"\t[-T enable bias-T on GPIO PIN 0 (works for rtl-sdr.com v3 dongles)]\n"
+		"\t[-D direct_sampling_mode (default: 0, 1 = I, 2 = Q, 3 = I below threshold, 4 = Q below threshold)]\n"
+		"\t[-D direct_sampling_threshold_frequency (default: 0 use tuner specific frequency threshold for 3 and 4)]\n"
 		"\tfilename (a '-' dumps samples to stdout)\n"
 		"\t (omitting the filename also uses stdout)\n"
 		"\n"
@@ -776,6 +778,8 @@ int main(int argc, char **argv)
 	int direct_sampling = 0;
 	int offset_tuning = 0;
 	int enable_biastee = 0;
+	enum rtlsdr_ds_mode ds_mode = RTLSDR_DS_IQ;
+	uint32_t ds_temp, ds_threshold = 0;
 	double crop = 0.0;
 	char *freq_optarg;
 	time_t next_tick;
@@ -786,7 +790,7 @@ int main(int argc, char **argv)
 	double (*window_fn)(int, int) = rectangle;
 	freq_optarg = "";
 
-	while ((opt = getopt(argc, argv, "f:i:s:t:d:g:p:e:w:c:F:1PDOTh")) != -1) {
+	while ((opt = getopt(argc, argv, "f:i:s:t:d:g:p:e:w:c:F:D:1POTh")) != -1) {
 		switch (opt) {
 		case 'f': // lower:upper:bin_size
 			freq_optarg = strdup(optarg);
@@ -845,7 +849,15 @@ int main(int argc, char **argv)
 			peak_hold = 1;
 			break;
 		case 'D':
-			direct_sampling = 1;
+			if(!optarg) {
+				direct_sampling = 1;
+			} else {
+				ds_temp = (uint32_t)( atofs(optarg) + 0.5 );
+				if (ds_temp <= RTLSDR_DS_Q_BELOW)
+					ds_mode = (enum rtlsdr_ds_mode)ds_temp;
+				else
+					ds_threshold = ds_temp;
+			}
 			break;
 		case 'O':
 			offset_tuning = 1;
@@ -919,6 +931,9 @@ int main(int argc, char **argv)
 		verbose_direct_sampling(dev, 1);
 	}
 
+	/* Set direct sampling with threshold */
+	rtlsdr_set_ds_mode(dev, ds_mode, ds_threshold);
+
 	if (offset_tuning) {
 		verbose_offset_tuning(dev);
 	}

src/rtl_tcp.c

@@ -107,6 +107,8 @@ void usage(void)
 		"\t[-d device index (default: 0)]\n"
 		"\t[-P ppm_error (default: 0)]\n"
 		"\t[-T enable bias-T on GPIO PIN 0 (works for rtl-sdr.com v3 dongles)]\n"
+		"\t[-D direct_sampling_mode (default: 0, 1 = I, 2 = Q, 3 = I below threshold, 4 = Q below threshold)]\n"
+		"\t[-D direct_sampling_threshold_frequency (default: 0 use tuner specific frequency threshold for 3 and 4)]\n"
 		"\t[-v increase verbosity (default: 0)]\n");
 	exit(1);
 }
@@ -470,6 +472,8 @@ int main(int argc, char **argv)
 	int wait_ir = 10000;
 	pthread_t thread_ir;
 	uint32_t frequency = 100000000, samp_rate = 2048000;
+	enum rtlsdr_ds_mode ds_mode = RTLSDR_DS_IQ;
+	uint32_t ds_temp, ds_threshold = 0;
 	struct sockaddr_in local, remote;
 	uint32_t buf_num = 0;
 	/* buf_len:
@@ -506,7 +510,7 @@ int main(int argc, char **argv)
 	struct sigaction sigact, sigign;
 #endif
 
-	while ((opt = getopt(argc, argv, "a:p:I:W:f:g:s:b:l:n:d:P:w:vT")) != -1) {
+	while ((opt = getopt(argc, argv, "a:p:I:W:f:g:s:b:l:n:d:P:w:D:vT")) != -1) {
 		switch (opt) {
 		case 'd':
 			dev_index = verbose_device_search(optarg);
@@ -554,6 +558,13 @@ int main(int argc, char **argv)
 		case 'T':
 			enable_biastee = 1;
 			break;
+		case 'D':
+			ds_temp = (uint32_t)( atofs(optarg) + 0.5 );
+			if (ds_temp <= RTLSDR_DS_Q_BELOW)
+				ds_mode = (enum rtlsdr_ds_mode)ds_temp;
+			else
+				ds_threshold = ds_temp;
+			break;
 		default:
 			usage();
 			break;
@@ -601,6 +612,9 @@ int main(int argc, char **argv)
 	if (r < 0)
 		fprintf(stderr, "WARNING: Failed to set sample rate.\n");
 
+	/* Set direct sampling with threshold */
+	rtlsdr_set_ds_mode(dev, ds_mode, ds_threshold);
+
 	/* Set the frequency */
 	r = rtlsdr_set_center_freq(dev, frequency);
 	if (r < 0)