B-Netz / NMT: minor changes at signal detection

src/bnetz/bnetz.c

@@ -505,11 +505,11 @@ void bnetz_receive_telegramm(bnetz_t *bnetz, uint16_t telegramm, double quality,
 {
 	int digit = 0;
 	int i;
-	int quality_percent = quality * 100;
-	int level_percent = level * 100;
+
+	PDEBUG(DFRAME, DEBUG_INFO, "RX Level: %.0f%% Quality=%.0f\n", level * 100.0 + 0.5, quality * 100.0 + 0.5);
 
 	/* drop any telegramm that is too bad */
-	if (quality_percent < 20)
+	if (quality < 0.2)
 		return;
 
 	for (i = 0; impulstelegramme[i].digit; i++) {
@@ -519,9 +519,9 @@ void bnetz_receive_telegramm(bnetz_t *bnetz, uint16_t telegramm, double quality,
 		}
 	}
 	if (digit == 0)
-		PDEBUG(DBNETZ, DEBUG_DEBUG, "Received unknown telegramm '0x%04x'. (quality=%d%% level=%d%%)\n", telegramm, quality_percent, level_percent);
+		PDEBUG(DBNETZ, DEBUG_DEBUG, "Received unknown telegramm '0x%04x'.\n", telegramm);
 	else
-		PDEBUG(DBNETZ, (bnetz->sender.loopback) ? DEBUG_NOTICE : DEBUG_DEBUG, "Received telegramm '%s'. (quality=%d%% level=%d%%)\n", impulstelegramme[i].description, quality_percent, level_percent);
+		PDEBUG(DBNETZ, (bnetz->sender.loopback) ? DEBUG_NOTICE : DEBUG_DEBUG, "Received telegramm '%s'.\n", impulstelegramme[i].description);
 
 	if (bnetz->sender.loopback) {
 		if (digit >= '0' && digit <= '9') {
@@ -661,7 +661,7 @@ void bnetz_receive_telegramm(bnetz_t *bnetz, uint16_t telegramm, double quality,
 		break;
 	case BNETZ_GESPRAECH:
 		/* only good telegramms shall pass */
-		if (quality_percent < 70)
+		if (quality < 0.7)
 			return;
 		if (digit == 't') {
 			PDEBUG(DBNETZ, DEBUG_NOTICE, "Received 'Schlusssignal' from mobile station\n");

src/nmt/dsp.c

@@ -303,41 +303,45 @@ static inline void fsk_decode_step(nmt_t *nmt, int pos)
 	nmt->rx_sample_count += nmt->fsk_filter_step;
 
 	level = audio_level(spl, max);
+	/* limit level to prevent division by zero */
+	if (level < 0.01)
+		level = 0.01;
 //	level = 0.63662 / 2.0;
 
 	audio_goertzel(spl, max, pos, nmt->fsk_coeff, result, 2);
 
 	/* calculate soft bit from both frequencies */
 	softbit = (result[1] / level - result[0] / level + 1.0) / 2.0;
+//printf("%.3f: %.3f\n", level, softbit);
 	/* scale it, since both filters overlap by some percent */
 #define MIN_QUALITY 0.33
 	softbit = (softbit - MIN_QUALITY) / (1.0 - MIN_QUALITY - MIN_QUALITY);
-	if (softbit > 1)
-		softbit = 1;
-	if (softbit < 0)
-		softbit = 0;
 #ifdef DEBUG_FILTER
 //	printf("|%s", show_level(result[0]/level*100));
 //	printf("|%s| low=%.3f high=%.3f level=%d\n", show_level(result[1]/level*100), result[0]/level, result[1]/level, (int)level);
 	printf("|%s| softbit=%.3f\n", show_level(softbit * 100), softbit);
 #endif
+	if (softbit > 1)
+		softbit = 1;
+	if (softbit < 0)
+		softbit = 0;
 	if (softbit > 0.5)
 		bit = 1;
 	else
 		bit = 0;
 
 	if (nmt->fsk_filter_bit != bit) {
+		/* if we have a bit change, reset sample counter to one half bit duration */
 #ifdef DEBUG_FILTER
 		puts("bit change");
 #endif
-		/* if we have a bit change, reset sample counter to one half bit duration */
 		nmt->fsk_filter_bit = bit;
 		nmt->fsk_filter_sample = 5;
 	} else if (--nmt->fsk_filter_sample == 0) {
+		/* if sample counter bit reaches 0, we reset sample counter to one bit duration */
 #ifdef DEBUG_FILTER
 		puts("sample");
 #endif
-		/* if sample counter bit reaches 0, we reset sample counter to one bit duration */
 //		quality = result[bit] / level;
 		if (softbit > 0.5)
 			quality = softbit * 2.0 - 1.0;

src/nmt/nmt.c

@@ -1124,9 +1124,10 @@ void nmt_receive_frame(nmt_t *nmt, const char *bits, double quality, double leve
 	frame_t frame;
 	int rc;
 
+	PDEBUG(DFRAME, DEBUG_INFO, "RX Level: %.0f%% Quality=%.0f\n", level * 100.0 + 0.5, quality * 100.0 + 0.5);
+
 	rc = decode_frame(&frame, bits, (nmt->sender.loopback) ? MTX_TO_XX : XX_TO_MTX, (nmt->state == STATE_MT_PAGING));
 	if (rc < 0) {
-		PDEBUG(DFRAME, DEBUG_INFO, "RX Level: %.0f%% Quality=%.0f\n", level * 100.0, quality * 100.0);
 		PDEBUG(DNMT, (nmt->sender.loopback) ? DEBUG_NOTICE : DEBUG_DEBUG, "Received invalid frame.\n");
 		return;
 	}
@@ -1134,7 +1135,6 @@ void nmt_receive_frame(nmt_t *nmt, const char *bits, double quality, double leve
 	/* frame counter */
 	nmt->rx_frame_count += (int)(frames_elapsed + 0.5);
 
-	PDEBUG(DFRAME, DEBUG_INFO, "RX Level: %.0f%% Quality=%.0f\n", level * 100.0, quality * 100.0);
 	PDEBUG(DNMT, (nmt->sender.loopback) ? DEBUG_NOTICE : DEBUG_DEBUG, "Received frame %s\n", nmt_frame_name(frame.index));
 
 	if (nmt->sender.loopback)