drivers/rc_input: ensure RC inversion is disabled initially and latch RC_INPUT_PROTO conservatively

- this allows jumping straight to a non-SBUS RC protocol
 - increased the scan time per protocol 300->500 ms, which the newer DSM parser seems to need in some cases.
 - only set RC_INPUT_PROTO if we've had a successful RC lock for > 3 seconds

src/drivers/rc_input/RCInput.cpp

@@ -48,12 +48,6 @@ RCInput::RCInput(const char *device) :
 	_cycle_perf(perf_alloc(PC_ELAPSED, MODULE_NAME": cycle time")),
 	_publish_interval_perf(perf_alloc(PC_INTERVAL, MODULE_NAME": publish interval"))
 {
-	// rc input, published to ORB
-	_rc_in.input_source = input_rc_s::RC_INPUT_SOURCE_PX4FMU_PPM;
-
-	// initialize it as RC lost
-	_rc_in.rc_lost = true;
-
 	// initialize raw_rc values and count
 	for (unsigned i = 0; i < input_rc_s::RC_INPUT_MAX_CHANNELS; i++) {
 		_raw_rc_values[i] = UINT16_MAX;
@@ -116,6 +110,8 @@ RCInput::init()
 	px4_arch_unconfiggpio(GPIO_PPM_IN);
 #endif // GPIO_PPM_IN
 
+	rc_io_invert(false);
+
 	return 0;
 }
 
@@ -271,8 +267,6 @@ void RCInput::set_rc_scan_state(RC_SCAN newState)
 
 	_rc_scan_begin = 0;
 	_rc_scan_locked = false;
-
-	_report_lock = true;
 }
 
 void RCInput::rc_io_invert(bool invert)
@@ -417,8 +411,8 @@ void RCInput::Run()
 		bool rc_updated = false;
 
 		// This block scans for a supported serial RC input and locks onto the first one found
-		// Scan for 300 msec, then switch protocol
-		constexpr hrt_abstime rc_scan_max = 300_ms;
+		// Scan for 500 msec, then switch protocol
+		constexpr hrt_abstime rc_scan_max = 500_ms;
 
 		unsigned frame_drops = 0;
 
@@ -434,6 +428,8 @@ void RCInput::Run()
 			_bytes_rx += newBytes;
 		}
 
+		const bool rc_scan_locked = _rc_scan_locked;
+
 		switch (_rc_scan_state) {
 		case RC_SCAN_NONE:
 			// do nothing
@@ -754,15 +750,18 @@ void RCInput::Run()
 			_rc_scan_locked = false;
 		}
 
-		if (_report_lock && _rc_scan_locked) {
-			_report_lock = false;
+		if (!rc_scan_locked && _rc_scan_locked) {
 			PX4_INFO("RC scan: %s RC input locked", RC_SCAN_STRING[_rc_scan_state]);
+		}
 
-			if (!_armed && (_param_rc_input_proto.get() < 0)) {
-				// RC_INPUT_PROTO auto => locked selection
-				_param_rc_input_proto.set(_rc_scan_state);
-				_param_rc_input_proto.commit();
-			}
+		// set RC_INPUT_PROTO if RC successfully locked for > 3 seconds
+		if (!_armed && rc_updated && _rc_scan_locked
+		    && ((_rc_scan_begin != 0) && hrt_elapsed_time(&_rc_scan_begin) > 3_s)
+		    && (_param_rc_input_proto.get() < 0)
+		   ) {
+			// RC_INPUT_PROTO auto => locked selection
+			_param_rc_input_proto.set(_rc_scan_state);
+			_param_rc_input_proto.commit();
 		}
 	}
 }

src/drivers/rc_input/RCInput.hpp

@@ -131,7 +131,6 @@ private:
 
 	bool _initialized{false};
 	bool _rc_scan_locked{false};
-	bool _report_lock{true};
 
 	static constexpr unsigned	_current_update_interval{4000}; // 250 Hz