From dc30197ca7a2c605767aed9aa76e534296e24c5a Mon Sep 17 00:00:00 2001
From: Peter Barker <pbarker@barker.dropbear.id.au>
Date: Mon, 1 Jan 2018 23:03:28 +1100
Subject: [PATCH] AP_AHRS: add AP::ahrs() singleton

---
 libraries/AP_AHRS/AP_AHRS.cpp | 12 ++++++++++++
 libraries/AP_AHRS/AP_AHRS.h   | 15 +++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/libraries/AP_AHRS/AP_AHRS.cpp b/libraries/AP_AHRS/AP_AHRS.cpp
index 7c14a7ffaa..954d194535 100644
--- a/libraries/AP_AHRS/AP_AHRS.cpp
+++ b/libraries/AP_AHRS/AP_AHRS.cpp
@@ -411,3 +411,15 @@ Vector2f AP_AHRS::rotate_body_to_earth2D(const Vector2f &bf) const
     return Vector2f(bf.x * _cos_yaw - bf.y * _sin_yaw,
                     bf.x * _sin_yaw + bf.y * _cos_yaw);
 }
+
+// singleton instance
+AP_AHRS *AP_AHRS::_singleton;
+
+namespace AP {
+
+AP_AHRS &ahrs()
+{
+    return *AP_AHRS::get_singleton();
+}
+
+}
diff --git a/libraries/AP_AHRS/AP_AHRS.h b/libraries/AP_AHRS/AP_AHRS.h
index 4a61ffca9f..9acb2e07c3 100644
--- a/libraries/AP_AHRS/AP_AHRS.h
+++ b/libraries/AP_AHRS/AP_AHRS.h
@@ -76,6 +76,8 @@ public:
         _sin_yaw(0.0f),
         _active_accel_instance(0)
     {
+        _singleton = this;
+
         // load default values from var_info table
         AP_Param::setup_object_defaults(this, var_info);
 
@@ -100,6 +102,11 @@ public:
     // empty virtual destructor
     virtual ~AP_AHRS() {}
 
+    // get singleton instance
+    static AP_AHRS *get_singleton() {
+        return _singleton;
+    }
+
     // init sets up INS board orientation
     virtual void init() {
         set_orientation();
@@ -670,6 +677,10 @@ protected:
     // AOA and SSA
     float _AOA, _SSA;
     uint32_t _last_AOA_update_ms;
+
+private:
+    static AP_AHRS *_singleton;
+
 };
 
 #include "AP_AHRS_DCM.h"
@@ -680,3 +691,7 @@ protected:
 #else
 #define AP_AHRS_TYPE AP_AHRS
 #endif
+
+namespace AP {
+    AP_AHRS &ahrs();
+};