C-Netz: Make demodulation algorithm (slope or leve) slectable via option

By default (auto), the algorithm is selected, depending on sound card
or SDR usage. For testing and debugging purpose, the algorithm can be
forced.

1 files changed, 37 insertions, 2 deletions

diff --git a/src/cnetz/main.c b/src/cnetz/main.c
index 0d4ee87..b4578e8 100644
--- a/src/cnetz/main.c
+++ b/src/cnetz/main.c
@@ -47,6 +47,7 @@ int set_clock_speed = 0;
 const char *flip_polarity = "auto";
 int ms_power = 0; /* 0..3 */
 int auth = 0;
+enum demod_type demod = FSK_DEMOD_AUTO;
 
 void print_help(const char *arg0)
 {
@@ -75,6 +76,15 @@ void print_help(const char *arg0)
 	printf("        Enable authentication on the base station. Since we cannot\n");
 	printf("	authenticate, because we don't know the secret key and the algorithm,\n");
 	printf("	we just accept any card. With this we get the vendor IDs of the phone.\n");
+	printf(" -D --demod auto | slope | level\n");
+	printf("        Adjust demodulation algorithm. Use 'slope' to detect a level change\n");
+	printf("        by finding the highest slope of a bit transition. It is useful, if\n");
+	printf("        the receiver drifts to 0 after a while, due to DC decoupling. This\n");
+	printf("        happens in every analog receiver and in every sound card input.\n");
+	printf("        Use 'level' to detect a level change by passing zero level. This\n");
+	printf("        requires a DC coupled signal, which is produced by SDR.\n");
+	printf("        Use 'auto' to select 'slope' for sound card input and 'level' for SDR\n");
+	printf("        input. (default = '%s')\n", (demod == FSK_DEMOD_LEVEL) ? "level" : (demod == FSK_DEMOD_SLOPE) ? "slope" : "auto");
 	printf("\nstation-id: Give 7 digit station-id, you don't need to enter it for every\n");
 	printf("        start of this program.\n");
 	print_hotkeys_common();
@@ -94,10 +104,11 @@ static int handle_options(int argc, char **argv)
 		{"flip-polarity", 1, 0, 'F'},
 		{"ms-power", 1, 0, 'P'},
 		{"authentication", 0, 0, 'A'},
+		{"demod", 1, 0, 'D'},
 		{0, 0, 0, 0}
 	};
 
-	set_options_common("T:MS:F:N:P:AV", long_options_special);
+	set_options_common("T:MS:F:N:P:AD:", long_options_special);
 
 	while (1) {
 		int option_index = 0, c;
@@ -161,6 +172,19 @@ static int handle_options(int argc, char **argv)
 			auth = 1;
 			skip_args += 1;
 			break;
+		case 'D':
+			if (!strcasecmp(optarg, "auto"))
+				demod = FSK_DEMOD_AUTO;
+			else if (!strcasecmp(optarg, "slope"))
+				demod = FSK_DEMOD_SLOPE;
+			else if (!strcasecmp(optarg, "level"))
+				demod = FSK_DEMOD_LEVEL;
+			else {
+				fprintf(stderr, "Given demodulation type '%s' is illegal, see help!\n", optarg);
+				exit(0);
+			}
+			skip_args += 2;
+			break;
 		default:
 			opt_switch_common(c, argv[0], &skip_args);
 		}
@@ -299,9 +323,20 @@ int main(int argc, char *argv[])
 	if (use_sdr && polarity == 0)
 		polarity = 1; /* SDR is always positive */
 
+	/* demodulation algorithm */
+	if (demod == FSK_DEMOD_AUTO)
+		demod = (use_sdr) ? FSK_DEMOD_LEVEL : FSK_DEMOD_SLOPE;
+	if (demod == FSK_DEMOD_LEVEL && !use_sdr) {
+		fprintf(stderr, "*******************************************************************************\n");
+		fprintf(stderr, "I strongly suggest to use 'slope' demodulation algorithm!!!\n");
+		fprintf(stderr, "Using sound card will cause the DC levels to return to 0. Using 'level' assumes\n");
+		fprintf(stderr, "that a frequency offset never returns to 0. (Use this only with SDR.)\n");
+		fprintf(stderr, "*******************************************************************************\n");
+	}
+
 	/* create transceiver instance */
 	for (i = 0; i < num_kanal; i++) {
-		rc = cnetz_create(kanal[i], chan_type[i], audiodev[i], use_sdr, samplerate, rx_gain, auth, ms_power, (i == 0) ? measure_speed : 0, clock_speed, polarity, do_pre_emphasis, do_de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback);
+		rc = cnetz_create(kanal[i], chan_type[i], audiodev[i], use_sdr, demod, samplerate, rx_gain, auth, ms_power, (i == 0) ? measure_speed : 0, clock_speed, polarity, do_pre_emphasis, do_de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback);
 		if (rc < 0) {
 			fprintf(stderr, "Failed to create \"Sender\" instance. Quitting!\n");
 			goto fail;