RC_Channel: added RC_PROTOCOLS mask

allows selection of supported protocols

libraries/RC_Channel/RC_Channel.h

@@ -419,6 +419,9 @@ public:
         return _override_timeout.get() * 1e3f;
     }
 
+    // get mask of enabled protocols
+    uint32_t enabled_protocols() const;
+
     // returns true if we have had a direct detach RC reciever, does not include overrides
     bool has_had_rc_receiver() const { return _has_had_rc_receiver; }
 
@@ -459,6 +462,7 @@ private:
 
     AP_Float _override_timeout;
     AP_Int32  _options;
+    AP_Int32  _protocols;
 
     // flight_mode_channel_number must be overridden in vehicle specific code
     virtual int8_t flight_mode_channel_number() const = 0;

libraries/RC_Channel/RC_Channels.cpp

@@ -224,6 +224,15 @@ bool RC_Channels::get_pwm(uint8_t c, uint16_t &pwm) const
     return true;
 }
 
+// return mask of enabled protocols.
+uint32_t RC_Channels::enabled_protocols() const
+{
+    if (_singleton == nullptr) {
+        // for example firmware
+        return 1U;
+    }
+    return uint32_t(_protocols.get());
+}
 
 // singleton instance
 RC_Channels *RC_Channels::_singleton;

libraries/RC_Channel/RC_Channels_VarInfo.h

@@ -92,5 +92,12 @@ const AP_Param::GroupInfo RC_Channels::var_info[] = {
     // @Bitmask: 0:Ignore RC Receiver, 1:Ignore MAVLink Overrides, 2:Ignore Receiver Failsafe, 3:FPort Pad, 4:Log RC input bytes, 5:Arming check throttle for 0 input, 6:Skip the arming check for neutral Roll/Pitch/Yay sticks, 7:Allow Switch reverse
     AP_GROUPINFO("_OPTIONS", 33, RC_CHANNELS_SUBCLASS, _options, (uint32_t)RC_Channels::Option::ARMING_CHECK_THROTTLE),
 
+    // @Param: _PROTOCOLS
+    // @DisplayName: RC protocols enabled
+    // @Description: Bitmask of enabled RC protocols. Allows narrowing the protocol detection to only specific types of RC receivers which can avoid issues with incorrect detection. Set to 1 to enable all protocols.
+    // @User: Advanced
+    // @Bitmask: 0:All,1:PPM,2:IBUS,3:SBUS,4:SBUS_NI,5:DSM,6:SUMD,7:SRXL,8:SRXL2,9:CRSF,10:ST24,11:FPORT
+    AP_GROUPINFO("_PROTOCOLS", 34, RC_CHANNELS_SUBCLASS, _protocols, 1),
+    
     AP_GROUPEND
 };