AMPS: Add option to be more tollerant to sync detection

Also it detects more false syncs, but this is ignored if decoding fails.

src/amps/amps.c

@@ -340,7 +340,7 @@ static amps_t *search_pc(void)
 static void amps_go_idle(amps_t *amps);
 
 /* Create transceiver instance and link to a list. */
-int amps_create(int channel, enum amps_chan_type chan_type, const char *sounddev, int samplerate, int cross_channels, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_wave, const char *read_wave, amps_si *si, uint16_t sid, uint8_t sat, int polarity, int loopback)
+int amps_create(int channel, enum amps_chan_type chan_type, const char *sounddev, int samplerate, int cross_channels, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_wave, const char *read_wave, amps_si *si, uint16_t sid, uint8_t sat, int polarity, int tolerant, int loopback)
 {
 	sender_t *sender;
 	amps_t *amps;
@@ -407,7 +407,7 @@ int amps_create(int channel, enum amps_chan_type chan_type, const char *sounddev
 	}
 
 	/* init audio processing */
-	rc = dsp_init_sender(amps, (de_emphasis == 0));
+	rc = dsp_init_sender(amps, (de_emphasis == 0), tolerant);
 	if (rc < 0) {
 		PDEBUG(DAMPS, DEBUG_ERROR, "Failed to init audio processing!\n");
 		goto error;

src/amps/amps.h

@@ -77,6 +77,7 @@ typedef struct amps {
 	double			fsk_rx_elapsed;		/* bit duration since last level change */
 	enum fsk_rx_sync	fsk_rx_sync;		/* sync state */
 	uint16_t		fsk_rx_sync_register;	/* shift register to detect sync word */
+	int			fsk_rx_sync_tolerant;	/* be more tolerant to sync */
 	/* the dotting buffer stores the elapsed samples, so we can calculate
 	 * an average time of zero-crossings during dotting sequence.
 	 * this buffer wrapps every 256 values */
@@ -160,7 +161,7 @@ const char *amps_min12number(uint32_t min1);
 void amps_number2min(const char *number, uint32_t *min1, uint16_t *min2);
 const char *amps_min2number(uint32_t min1, uint16_t min2);
 const char *amps_scm(uint8_t scm);
-int amps_create(int channel, enum amps_chan_type chan_type, const char *sounddev, int samplerate, int cross_channels, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_wave, const char *read_wave, amps_si *si, uint16_t sid, uint8_t sat, int polarity, int loopback);
+int amps_create(int channel, enum amps_chan_type chan_type, const char *sounddev, int samplerate, int cross_channels, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_wave, const char *read_wave, amps_si *si, uint16_t sid, uint8_t sat, int polarity, int tolerant, int loopback);
 void amps_destroy(sender_t *sender);
 void amps_rx_signaling_tone(amps_t *amps, int tone, double quality);
 void amps_rx_sat(amps_t *amps, int tone, double quality);

src/amps/dsp.c

@@ -125,6 +125,8 @@ static double sat_freq[5] = {
 
 static int dsp_sine_sat[256];
 
+static uint8_t dsp_sync_check[0x800];
+
 /* global init for FSK */
 void dsp_init(void)
 {
@@ -136,6 +138,17 @@ void dsp_init(void)
 		s = sin((double)i / 256.0 * 2.0 * PI);
 		dsp_sine_sat[i] = (int)(s * SAT_DEVIATION);
 	}
+
+	/* sync checker */
+	for (i = 0; i < 0x800; i++) {
+		dsp_sync_check[i] = 0xff; /* no sync */
+	}
+	for (i = 0; i < 11; i++) {
+		dsp_sync_check[0x712 ^ (1 << i)] = 0x01; /* one bit error */
+		dsp_sync_check[0x0ed ^ (1 << i)] = 0x81; /* one bit error */
+	}
+	dsp_sync_check[0x712] = 0x00; /* no bit error */
+	dsp_sync_check[0x0ed] = 0x80; /* no bit error */
 }
 
 static void dsp_init_ramp(amps_t *amps)
@@ -160,7 +173,7 @@ static void dsp_init_ramp(amps_t *amps)
 static void sat_reset(amps_t *amps, const char *reason);
 
 /* Init FSK of transceiver */
-int dsp_init_sender(amps_t *amps, int high_pass)
+int dsp_init_sender(amps_t *amps, int high_pass, int tolerant)
 {
 	double coeff;
 	int16_t *spl;
@@ -240,6 +253,9 @@ int dsp_init_sender(amps_t *amps, int high_pass)
 		amps->highpass_factor = RC / (RC + dt);
 	}
 
+	/* be more tolerant when syncing */
+	amps->fsk_rx_sync_tolerant = tolerant;
+
 	return 0;
 
 error:
@@ -508,7 +524,11 @@ static void fsk_rx_bit(amps_t *amps, int16_t *spl, int len, int pos, int begin,
 	if (amps->fsk_rx_sync != FSK_SYNC_POSITIVE && amps->fsk_rx_sync != FSK_SYNC_NEGATIVE) {
 		amps->fsk_rx_sync_register = (amps->fsk_rx_sync_register << 1) | bit;
 		/* check if we received a sync */
-		if ((amps->fsk_rx_sync_register & 0x7ff) == 0x712) {
+		switch (dsp_sync_check[amps->fsk_rx_sync_register & 0x7ff]) {
+		case 0x01:
+			if (!amps->fsk_rx_sync_tolerant)
+				break;
+		case 0x00:
 #ifdef DEBUG_DECODER
 			printf("Sync word detected (positive)\n");
 #endif
@@ -520,8 +540,10 @@ prepare_frame:
 			amps->fsk_rx_sync_register = 0x555;
 			amps->when_received = get_time() - (21.0 / (double)BITRATE);
 			return;
-		}
+		case 0x81:
-		if ((amps->fsk_rx_sync_register & 0x7ff) == 0x0ed) {
+			if (!amps->fsk_rx_sync_tolerant)
+				break;
+		case 0x80:
 #ifdef DEBUG_DECODER
 			printf("Sync word detected (negative)\n");
 #endif

src/amps/dsp.h

@@ -1,6 +1,6 @@
 
 void dsp_init(void);
-int dsp_init_sender(amps_t *amps, int high_pass);
+int dsp_init_sender(amps_t *amps, int high_pass, int tolerant);
 void dsp_cleanup_sender(amps_t *amps);
 void amps_set_dsp_mode(amps_t *amps, enum dsp_mode mode, int frame_length);
 

src/amps/main.c

@@ -45,6 +45,7 @@ int num_chan_type = 0;
 enum amps_chan_type chan_type[MAX_SENDER] = { CHAN_TYPE_CC_PC_VC };
 const char *flip_polarity = "";
 int ms_power = 4, dcc = 0, scc = 0, sid = 40, regh = 1, regr = 1, pureg = 1, pdreg = 1, locaid = -1, regincr = 300, bis = 0;
+int tolerant = 0;
 
 void print_help(const char *arg0)
 {
@@ -86,6 +87,8 @@ void print_help(const char *arg0)
 	printf(" -S --sysinfo bis=0 | bis=1\n");
 	printf("        If 0, phone ignores BUSY/IDLE bit on FOCC (default = '%d')\n", bis);
 	printf("        If 1, be sure to have a round-trip delay (latency) not more than 5 ms\n");
+	printf(" -T --tolerant\n");
+	printf("        Be more tolerant when hunting for sync sequence\n");
 	printf("\nstation-id: Give 10 digit station-id, you don't need to enter it for every\n");
 	printf("        start of this program.\n");
 }
@@ -101,10 +104,11 @@ static int handle_options(int argc, char **argv)
 		{"flip-polarity", 1, 0, 'F'},
 		{"ms-power", 1, 0, 'P'},
 		{"sysinfo", 1, 0, 'S'},
+		{"tolerant", 0, 0, 'T'},
 		{0, 0, 0, 0}
 	};
 
-	set_options_common("t:F:P:S:", long_options_special);
+	set_options_common("t:F:P:S:T", long_options_special);
 
 	while (1) {
 		int option_index = 0, c;
@@ -207,6 +211,10 @@ static int handle_options(int argc, char **argv)
 			}
 			skip_args += 2;
 			break;
+		case 'T':
+			tolerant = 1;
+			skip_args += 1;
+			break;
 		default:
 			opt_switch_common(c, argv[0], &skip_args);
 		}
@@ -341,7 +349,7 @@ int main(int argc, char *argv[])
 		amps_si si;
 
 		init_sysinfo(&si, ms_power, ms_power, dcc, sid >> 1, regh, regr, pureg, pdreg, locaid, regincr, bis);
-		rc = amps_create(kanal[i], chan_type[i], sounddev[i], samplerate, cross_channels, rx_gain, do_pre_emphasis, do_de_emphasis, write_wave, read_wave, &si, sid, scc, polarity, loopback);
+		rc = amps_create(kanal[i], chan_type[i], sounddev[i], samplerate, cross_channels, rx_gain, do_pre_emphasis, do_de_emphasis, write_wave, read_wave, &si, sid, scc, polarity, tolerant, loopback);
 		if (rc < 0) {
 			fprintf(stderr, "Failed to create \"Sender\" instance. Quitting!\n");
 			goto fail;