From faf49934362187575f976bf31b5aba764b7d5325 Mon Sep 17 00:00:00 2001
From: Hwurzburg <hwurzburg@yahoo.com>
Date: Tue, 18 May 2021 10:20:49 -0500
Subject: [PATCH] AP_Fence: add pre-arm check for fence enabled but none
 selected

---
 libraries/AC_Fence/AC_Fence.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libraries/AC_Fence/AC_Fence.cpp b/libraries/AC_Fence/AC_Fence.cpp
index 04fd0992f7..47b4f5e102 100644
--- a/libraries/AC_Fence/AC_Fence.cpp
+++ b/libraries/AC_Fence/AC_Fence.cpp
@@ -282,6 +282,12 @@ bool AC_Fence::pre_arm_check(const char* &fail_msg) const
 {
     fail_msg = nullptr;
 
+    // if fences are enabled but none selected fail pre-arm check
+    if (enabled() && !present()) {
+        fail_msg = "Fences enabled, but none selected";
+        return false;
+    }
+
     // if not enabled or not fence set-up always return true
     if ((!_enabled && !_auto_enabled) || !_enabled_fences) {
         return true;