From 4d944da530fe162d8dcd58fce3594bd9ec5ab98c Mon Sep 17 00:00:00 2001
From: Peter Barker <pbarker@barker.dropbear.id.au>
Date: Fri, 6 Apr 2018 22:17:04 +1000
Subject: [PATCH] AP_AHRS: add a singleton-getter cast into AP_AHRS_NavEKF

This will allow libraries which absolutely require the EKF to easily get
a cast copy of the singleton.
---
 libraries/AP_AHRS/AP_AHRS.h          | 6 ++++++
 libraries/AP_AHRS/AP_AHRS_NavEKF.cpp | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/libraries/AP_AHRS/AP_AHRS.h b/libraries/AP_AHRS/AP_AHRS.h
index c1a8d62f0d..d6fd37fe4d 100644
--- a/libraries/AP_AHRS/AP_AHRS.h
+++ b/libraries/AP_AHRS/AP_AHRS.h
@@ -686,4 +686,10 @@ private:
 
 namespace AP {
     AP_AHRS &ahrs();
+
+    // use ahrs_navekf() only where the AHRS interface doesn't expose the
+    // functionality you require:
+#if AP_AHRS_NAVEKF_AVAILABLE
+    AP_AHRS_NavEKF &ahrs_navekf();
+#endif
 };
diff --git a/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp b/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
index a68bb8a464..9383e308f4 100644
--- a/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
+++ b/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
@@ -1642,5 +1642,11 @@ uint8_t AP_AHRS_NavEKF::get_primary_gyro_index(void) const
     return AP::ins().get_primary_gyro();
 }
 
+
+AP_AHRS_NavEKF &AP::ahrs_navekf()
+{
+    return static_cast<AP_AHRS_NavEKF&>(*AP_AHRS::get_singleton());
+}
+
 #endif // AP_AHRS_NAVEKF_AVAILABLE