px4iofirmware: guard against parsing multiple RC protocols

It was for example possible that DSM got parsed, and in the next iteration
SBUS got parsed, leading to multiple PX4IO_P_STATUS_FLAGS_RC_ flags set.
input_rc::input_source was then incorrectly set to DSM.

Partially guarding was already done: if SBUS got parsed, DSM and others
were skipped.

The IO will still clear all PX4IO_P_STATUS_FLAGS_RC_* flags on RC loss.

src/modules/px4iofirmware/controls.c

@@ -133,11 +133,13 @@ bool dsm_port_input(uint16_t *rssi, bool *dsm_updated, bool *st24_updated, bool
 
 	*st24_updated = false;
 
-	for (unsigned i = 0; i < n_bytes; i++) {
-		/* set updated flag if one complete packet was parsed */
-		st24_rssi = RC_INPUT_RSSI_MAX;
-		*st24_updated |= (OK == st24_decode(bytes[i], &st24_rssi, &lost_count,
-						    &st24_channel_count, r_raw_rc_values, PX4IO_RC_INPUT_CHANNELS));
+	if (!(r_status_flags & (PX4IO_P_STATUS_FLAGS_RC_DSM | PX4IO_P_STATUS_FLAGS_RC_SUMD))) {
+		for (unsigned i = 0; i < n_bytes; i++) {
+			/* set updated flag if one complete packet was parsed */
+			st24_rssi = RC_INPUT_RSSI_MAX;
+			*st24_updated |= (OK == st24_decode(bytes[i], &st24_rssi, &lost_count,
+							    &st24_channel_count, r_raw_rc_values, PX4IO_RC_INPUT_CHANNELS));
+		}
 	}
 
 	if (*st24_updated && lost_count == 0) {
@@ -161,11 +163,13 @@ bool dsm_port_input(uint16_t *rssi, bool *dsm_updated, bool *st24_updated, bool
 
 	*sumd_updated = false;
 
-	for (unsigned i = 0; i < n_bytes; i++) {
-		/* set updated flag if one complete packet was parsed */
-		sumd_rssi = RC_INPUT_RSSI_MAX;
-		*sumd_updated |= (OK == sumd_decode(bytes[i], &sumd_rssi, &sumd_rx_count,
-						    &sumd_channel_count, r_raw_rc_values, PX4IO_RC_INPUT_CHANNELS, &sumd_failsafe_state));
+	if (!(r_status_flags & (PX4IO_P_STATUS_FLAGS_RC_DSM | PX4IO_P_STATUS_FLAGS_RC_ST24))) {
+		for (unsigned i = 0; i < n_bytes; i++) {
+			/* set updated flag if one complete packet was parsed */
+			sumd_rssi = RC_INPUT_RSSI_MAX;
+			*sumd_updated |= (OK == sumd_decode(bytes[i], &sumd_rssi, &sumd_rx_count,
+							    &sumd_channel_count, r_raw_rc_values, PX4IO_RC_INPUT_CHANNELS, &sumd_failsafe_state));
+		}
 	}
 
 	if (*sumd_updated) {
@@ -263,35 +267,39 @@ controls_tick()
 	perf_begin(c_gather_sbus);
 #endif
 
-	bool sbus_failsafe, sbus_frame_drop;
-	bool sbus_updated = sbus_input(_sbus_fd, r_raw_rc_values, &r_raw_rc_count, &sbus_failsafe, &sbus_frame_drop,
-				       PX4IO_RC_INPUT_CHANNELS);
+	bool sbus_updated = false;
 
-	if (sbus_updated) {
-		atomic_modify_or(&r_status_flags, PX4IO_P_STATUS_FLAGS_RC_SBUS);
+	if (!(r_status_flags & (PX4IO_P_STATUS_FLAGS_RC_DSM | PX4IO_P_STATUS_FLAGS_RC_ST24 | PX4IO_P_STATUS_FLAGS_RC_SUMD))) {
+		bool sbus_failsafe, sbus_frame_drop;
+		sbus_updated = sbus_input(_sbus_fd, r_raw_rc_values, &r_raw_rc_count, &sbus_failsafe, &sbus_frame_drop,
+					  PX4IO_RC_INPUT_CHANNELS);
 
-		unsigned sbus_rssi = RC_INPUT_RSSI_MAX;
+		if (sbus_updated) {
+			atomic_modify_or(&r_status_flags, PX4IO_P_STATUS_FLAGS_RC_SBUS);
 
-		if (sbus_frame_drop) {
-			r_raw_rc_flags |= PX4IO_P_RAW_RC_FLAGS_FRAME_DROP;
-			sbus_rssi = RC_INPUT_RSSI_MAX / 2;
+			unsigned sbus_rssi = RC_INPUT_RSSI_MAX;
 
-		} else {
-			r_raw_rc_flags &= ~(PX4IO_P_RAW_RC_FLAGS_FRAME_DROP);
-		}
+			if (sbus_frame_drop) {
+				r_raw_rc_flags |= PX4IO_P_RAW_RC_FLAGS_FRAME_DROP;
+				sbus_rssi = RC_INPUT_RSSI_MAX / 2;
 
-		if (sbus_failsafe) {
-			r_raw_rc_flags |= PX4IO_P_RAW_RC_FLAGS_FAILSAFE;
+			} else {
+				r_raw_rc_flags &= ~(PX4IO_P_RAW_RC_FLAGS_FRAME_DROP);
+			}
 
-		} else {
-			r_raw_rc_flags &= ~(PX4IO_P_RAW_RC_FLAGS_FAILSAFE);
-		}
+			if (sbus_failsafe) {
+				r_raw_rc_flags |= PX4IO_P_RAW_RC_FLAGS_FAILSAFE;
 
-		/* set RSSI to an emulated value if ADC RSSI is off */
-		if (!(r_setup_features & PX4IO_P_SETUP_FEATURES_ADC_RSSI)) {
-			_rssi = sbus_rssi;
-		}
+			} else {
+				r_raw_rc_flags &= ~(PX4IO_P_RAW_RC_FLAGS_FAILSAFE);
+			}
 
+			/* set RSSI to an emulated value if ADC RSSI is off */
+			if (!(r_setup_features & PX4IO_P_SETUP_FEATURES_ADC_RSSI)) {
+				_rssi = sbus_rssi;
+			}
+
+		}
 	}
 
 #if defined(PX4IO_PERF)
@@ -321,7 +329,7 @@ controls_tick()
 
 	bool dsm_updated = false, st24_updated = false, sumd_updated = false;
 
-	if (!((r_status_flags & PX4IO_P_STATUS_FLAGS_RC_SBUS) || (r_status_flags & PX4IO_P_STATUS_FLAGS_RC_PPM))) {
+	if (!(r_status_flags & (PX4IO_P_STATUS_FLAGS_RC_SBUS | PX4IO_P_STATUS_FLAGS_RC_PPM))) {
 #if defined(PX4IO_PERF)
 		perf_begin(c_gather_dsm);
 #endif