r82xx: set_dithering()

Author: keenerd

include/rtl-sdr.h

@@ -322,6 +322,17 @@ RTLSDR_API int rtlsdr_set_offset_tuning(rtlsdr_dev_t *dev, int on);
  */
 RTLSDR_API int rtlsdr_get_offset_tuning(rtlsdr_dev_t *dev);
 
+/*!
+ * Enable or disable frequency dithering for r820t tuners.
+ * Must be performed before freq_set().
+ * Fails for other tuners.
+ *
+ * \param dev the device handle given by rtlsdr_open()
+ * \param on 0 means disabled, 1 enabled
+ * \return 0 on success
+ */
+RTLSDR_API int rtlsdr_set_dithering(rtlsdr_dev_t *dev, int dither);
+
 /* streaming functions */
 
 RTLSDR_API int rtlsdr_reset_buffer(rtlsdr_dev_t *dev);

include/tuner_r82xx.h

@@ -84,6 +84,7 @@ struct r82xx_priv {
 	uint8_t				input;
 	int				has_lock;
 	int				init_done;
+	int				disable_dither;
 
 	/* Store current mode */
 	uint32_t			delsys;
@@ -116,5 +117,6 @@ int r82xx_init(struct r82xx_priv *priv);
 int r82xx_set_freq(struct r82xx_priv *priv, uint32_t freq);
 int r82xx_set_gain(struct r82xx_priv *priv, int set_manual_gain, int gain);
 int r82xx_set_nomod(struct r82xx_priv *priv);
+int r82xx_set_dither(struct r82xx_priv *priv, int dither);
 
 #endif

src/librtlsdr.c

@@ -1266,6 +1266,14 @@ int rtlsdr_get_offset_tuning(rtlsdr_dev_t *dev)
 	return (dev->offs_freq) ? 1 : 0;
 }
 
+int rtlsdr_set_dithering(rtlsdr_dev_t *dev, int dither)
+{
+	if (dev->tuner_type == RTLSDR_TUNER_R820T) {
+		return r82xx_set_dither(&dev->r82xx_p, dither);
+	}
+	return 1;
+}
+
 static rtlsdr_dongle_t *find_known_device(uint16_t vid, uint16_t pid)
 {
 	unsigned int i;

src/rtl_sdr.c

@@ -56,6 +56,7 @@ void usage(void)
 		"\t[-n number of samples to read (default: 0, infinite)]\n"
 		"\t[-S force sync output (default: async)]\n"
 		"\t[-D direct_sampling_mode, 0 (default/off), 1 (I), 2 (Q), 3 (no-mod)]\n"
+		"\t[-N no dithering (default: use dithering)]\n"
 		"\tfilename (a '-' dumps samples to stdout)\n\n");
 	exit(1);
 }
@@ -115,6 +116,7 @@ int main(int argc, char **argv)
 	int ppm_error = 0;
 	int sync_mode = 0;
 	int direct_sampling = 0;
+	int dithering = 1;
 	FILE *file;
 	uint8_t *buffer;
 	int dev_index = 0;
@@ -123,7 +125,7 @@ int main(int argc, char **argv)
 	uint32_t samp_rate = DEFAULT_SAMPLE_RATE;
 	uint32_t out_block_size = DEFAULT_BUF_LENGTH;
 
-	while ((opt = getopt(argc, argv, "d:f:g:s:b:n:p:D:S")) != -1) {
+	while ((opt = getopt(argc, argv, "d:f:g:s:b:n:p:D:SN")) != -1) {
 		switch (opt) {
 		case 'd':
 			dev_index = verbose_device_search(optarg);
@@ -153,6 +155,9 @@ int main(int argc, char **argv)
 		case 'D':
 			direct_sampling = atoi(optarg);
 			break;
+		case 'N':
+			dithering = 0;
+			break;
 		default:
 			usage();
 			break;
@@ -203,6 +208,16 @@ int main(int argc, char **argv)
 	SetConsoleCtrlHandler( (PHANDLER_ROUTINE) sighandler, TRUE );
 #endif
 
+	if (!dithering) {
+		fprintf(stderr, "Disabling dithering...  ");
+		r = rtlsdr_set_dithering(dev, dithering);
+		if (r) {
+			fprintf(stderr, "failure\n");
+		} else {
+			fprintf(stderr, "success\n");
+		}
+	}
+
 	if (direct_sampling) {
 		verbose_direct_sampling(dev, direct_sampling);
 	}

src/tuner_r82xx.c

@@ -506,7 +506,10 @@ static int r82xx_set_pll(struct r82xx_priv *priv, uint32_t freq)
 	else
 		val = 0x00;
 
-	rc = r82xx_write_reg_mask(priv, 0x12, val, 0x08);
+	if (priv->disable_dither)
+		val |= 0x10;
+
+	rc = r82xx_write_reg_mask(priv, 0x12, val, 0x18);
 	if (rc < 0)
 		return rc;
 
@@ -1142,7 +1145,11 @@ int r82xx_set_nomod(struct r82xx_priv *priv)
 	return rc;
 }
 
-
+int r82xx_set_dither(struct r82xx_priv *priv, int dither)
+{
+	priv->disable_dither = !dither;
+	return 0;
+}
 
 /*
  * r82xx standby logic