rtl_fm: fix auto/manual gain

Signed-off-by: Steve Markgraf <steve@steve-m.de>

src/rtl_fm.c

@@ -60,6 +60,7 @@
 #define MINIMAL_BUF_LENGTH		512
 #define MAXIMAL_BUF_LENGTH		(256 * 16384)
 #define CONSEQ_SQUELCH			4
+#define AUTO_GAIN			-100
 
 static pthread_t demod_thread;
 static sem_t data_ready;
@@ -103,7 +104,7 @@ void usage(void)
 		"\t (use multiple -f for scanning)\n"
 		"\t[-s samplerate (default: 24000 Hz)]\n"
 		"\t[-d device_index (default: 0)]\n"
-		"\t[-g tuner_gain (default: -1dB)]\n"
+		"\t[-g tuner_gain (default: automatic)]\n"
 		"\t[-l squelch_level (default: 150)]\n"
 		"\t[-E freq sets lower edge (default: center)]\n"
 		"\tfilename (a '-' dumps samples to stdout)\n\n"
@@ -439,7 +440,7 @@ int main(int argc, char **argv)
 	char *filename = NULL;
 	int n_read;
 	int r, opt;
-	int i, gain = -10; // tenths of a dB
+	int i, gain = AUTO_GAIN; // tenths of a dB
 	uint8_t *buffer;
 	uint32_t dev_index = 0;
 	int device_count;
@@ -538,11 +539,19 @@ int main(int argc, char **argv)
 	build_fir(&fm);
 
 	/* Set the tuner gain */
+	if (gain == AUTO_GAIN) {
+		r = rtlsdr_set_tuner_gain_mode(dev, 0);
+	} else {
+		r = rtlsdr_set_tuner_gain_mode(dev, 1);
 		r = rtlsdr_set_tuner_gain(dev, gain);
-	if (r < 0)
+	}
+	if (r != 0) {
 		fprintf(stderr, "WARNING: Failed to set tuner gain.\n");
-	else
+	} else if (gain == AUTO_GAIN) {
+		fprintf(stderr, "Tuner gain set to automatic.\n");
+	} else {
 		fprintf(stderr, "Tuner gain set to %0.2f dB.\n", gain/10.0);
+	}
 
 	if(strcmp(filename, "-") == 0) { /* Write samples to stdout */
 		fm.file = stdout;