AP_WheelEncoder: add singleton

libraries/AP_WheelEncoder/AP_WheelEncoder.cpp

@@ -151,6 +151,8 @@ const AP_Param::GroupInfo AP_WheelEncoder::var_info[] = {
 
 AP_WheelEncoder::AP_WheelEncoder(void)
 {
+    _singleton = this;
+
     AP_Param::setup_object_defaults(this, var_info);
 }
 
@@ -347,3 +349,15 @@ uint32_t AP_WheelEncoder::get_last_reading_ms(uint8_t instance) const
     }
     return state[instance].last_reading_ms;
 }
+
+// singleton instance
+AP_WheelEncoder *AP_WheelEncoder::_singleton;
+
+namespace AP {
+
+AP_WheelEncoder *wheelencoder()
+{
+    return AP_WheelEncoder::get_singleton();
+}
+
+}

libraries/AP_WheelEncoder/AP_WheelEncoder.h

@@ -39,6 +39,11 @@ public:
     AP_WheelEncoder(const AP_WheelEncoder &other) = delete;
     AP_WheelEncoder &operator=(const AP_WheelEncoder&) = delete;
 
+    // get singleton instance
+    static AP_WheelEncoder *get_singleton() {
+        return _singleton;
+    }
+
     // WheelEncoder driver types
     enum WheelEncoder_Type : uint8_t {
         WheelEncoder_TYPE_NONE             =   0,
@@ -121,4 +126,12 @@ protected:
     AP_WheelEncoder_Backend *drivers[WHEELENCODER_MAX_INSTANCES];
     uint8_t num_instances;
     Vector3f pos_offset_zero;   // allows returning position offsets of zero for invalid requests
+
+private:
+
+    static AP_WheelEncoder *_singleton;
 };
+
+namespace AP {
+    AP_WheelEncoder *wheelencoder();
+}