AP_Motors: make a singleton

this is used by AP_ESCSerial

libraries/AP_Motors/AP_Motors_Class.cpp

@@ -26,6 +26,9 @@
 
 extern const AP_HAL::HAL& hal;
 
+// singleton instance
+AP_Motors *AP_Motors::_instance;
+
 // Constructor
 AP_Motors::AP_Motors(uint16_t loop_rate, uint16_t speed_hz) :
     _loop_rate(loop_rate),
@@ -40,6 +43,8 @@ AP_Motors::AP_Motors(uint16_t loop_rate, uint16_t speed_hz) :
     _air_density_ratio(1.0f),
     _motor_fast_mask(0)
 {
+    _instance = this;
+    
     // init other flags
     _flags.armed = false;
     _flags.interlock = false;

libraries/AP_Motors/AP_Motors_Class.h

@@ -59,6 +59,9 @@ public:
     // Constructor
     AP_Motors(uint16_t loop_rate, uint16_t speed_hz = AP_MOTORS_SPEED_DEFAULT);
 
+    // singleton support
+    static AP_Motors *get_instance(void) { return _instance; }
+
     // check initialisation succeeded
     bool                initialised_ok() const { return _flags.initialised_ok; }
 
@@ -207,10 +210,13 @@ protected:
     uint16_t            _motor_fast_mask;
 
     // pass through variables
-    float _roll_radio_passthrough = 0.0f;     // roll input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed
-    float _pitch_radio_passthrough = 0.0f;    // pitch input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed
-    float _throttle_radio_passthrough = 0.0f; // throttle/collective input from pilot in 0 ~ 1 range.  used for setup and providing servo feedback while landed
-    float _yaw_radio_passthrough = 0.0f;      // yaw input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed
+    float _roll_radio_passthrough;     // roll input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed
+    float _pitch_radio_passthrough;    // pitch input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed
+    float _throttle_radio_passthrough; // throttle/collective input from pilot in 0 ~ 1 range.  used for setup and providing servo feedback while landed
+    float _yaw_radio_passthrough;      // yaw input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed
 
     AP_Int8             _pwm_type;            // PWM output type
+
+private:
+    static AP_Motors *_instance;
 };