AP_Param: add singleton

libraries/AP_Param/AP_Param.cpp

@@ -38,6 +38,9 @@ extern const AP_HAL::HAL &hal;
 
 uint16_t AP_Param::sentinal_offset;
 
+// singleton instance
+AP_Param *AP_Param::_singleton;
+
 #define ENABLE_DEBUG 1
 
 #if ENABLE_DEBUG
@@ -379,6 +382,14 @@ bool AP_Param::get_base(const struct Info &info, ptrdiff_t &base)
     return true;
 }
 
+namespace AP {
+
+AP_Param *param()
+{
+    return AP_Param::get_singleton();
+}
+
+}
 
 // find the info structure given a header and a group_info table
 // return the Info structure and a pointer to the variables storage

libraries/AP_Param/AP_Param.h

@@ -197,6 +197,11 @@ public:
         uint16_t i;
         for (i=0; info[i].type != AP_PARAM_NONE; i++) ;
         _num_vars = i;
+
+        if (_singleton != nullptr) {
+            AP_HAL::panic("AP_Param must be singleton");
+        }
+        _singleton = this;
     }
 
     // empty constructor
@@ -479,7 +484,11 @@ public:
                              AP_HAL::BetterStream *port);
 #endif // AP_PARAM_KEY_DUMP
 
+    static AP_Param *get_singleton() { return _singleton; }
+
 private:
+    static AP_Param *_singleton;
+
     /// EEPROM header
     ///
     /// This structure is placed at the head of the EEPROM to indicate
@@ -673,6 +682,10 @@ private:
     void save_io_handler(void);
 };
 
+namespace AP {
+    AP_Param *param();
+};
+
 /// Template class for scalar variables.
 ///
 /// Objects of this type have a value, and can be treated in many ways as though they