Fixed overflowing tslc.

src/modules/mavlink/mavlink_receiver.cpp

@@ -2295,12 +2295,30 @@ MavlinkReceiver::handle_message_utm_global_position(mavlink_message_t *msg)
 	t.lon = utm_pos.lon * 1e-7;
 	t.altitude = utm_pos.alt / 1000.0f;
 	t.altitude_type = ADSB_ALTITUDE_TYPE_GEOMETRIC;
+	// UTM_GLOBAL_POSIION uses NED (north, east, down) coordinates for velocity, in cm / s.
 	t.heading = atan2f(vy, vx);
 	t.hor_velocity = sqrtf(vy * vy + vx * vx);
 	t.ver_velocity = -vz;
 	// TODO: Callsign
+	// For now, set it to all 0s. This is a null-terminated string, so not explicitly giving it a null
+	// terminator could cause problems.
+	memset(&t.callsign[0], 0, sizeof(t.callsign));
 	t.emitter_type = ADSB_EMITTER_TYPE_NO_INFO;  // TODO: Is this correct?
-	t.tslc = _last_utm_global_pos_com == 0 ? 0 : (t.timestamp - _last_utm_global_pos_com) / 1000000;
+
+	// The Mavlink docs do not specify what to do if tslc (time since last communication) is out of range of
+	// an 8-bit int, or if this is the first communication.
+	// Here, I assume that if this is the first communication, tslc = 0.
+	// If tslc > 255, then tslc = 255.
+	unsigned long time_passed = (t.timestamp - _last_utm_global_pos_com) / 1000000;
+
+	if (_last_utm_global_pos_com == 0) {
+		time_passed = 0;
+
+	} else if (time_passed > UINT8_MAX) {
+		time_passed = UINT8_MAX;
+	}
+
+	t.tslc = (uint8_t) time_passed;
 
 	t.flags = 0;
 
@@ -2320,6 +2338,13 @@ MavlinkReceiver::handle_message_utm_global_position(mavlink_message_t *msg)
 	// Note: t.flags has deliberately NOT set VALID_CALLSIGN or VALID_SQUAWK, because UTM_GLOBAL_POSITION does not
 	// provide these.
 
+	if (_transponder_report_pub == nullptr) {
+		_transponder_report_pub = orb_advertise_queue(ORB_ID(transponder_report), &t, transponder_report_s::ORB_QUEUE_LENGTH);
+
+	} else {
+		orb_publish(ORB_ID(transponder_report), _transponder_report_pub, &t);
+	}
+
 	_last_utm_global_pos_com = t.timestamp;
 }