From 0e2b3781aec055be6b7ad6fd562b0c03a4c9033e Mon Sep 17 00:00:00 2001
From: Peter Barker <pbarker@barker.dropbear.id.au>
Date: Fri, 18 Nov 2016 18:52:15 +1100
Subject: [PATCH] AP_Gripper: a valid() method

---
 libraries/AP_Gripper/AP_Gripper.cpp       | 1 +
 libraries/AP_Gripper/AP_Gripper.h         | 3 +++
 libraries/AP_Gripper/AP_Gripper_Backend.h | 3 +++
 3 files changed, 7 insertions(+)

diff --git a/libraries/AP_Gripper/AP_Gripper.cpp b/libraries/AP_Gripper/AP_Gripper.cpp
index 30411405b6..7392c01030 100644
--- a/libraries/AP_Gripper/AP_Gripper.cpp
+++ b/libraries/AP_Gripper/AP_Gripper.cpp
@@ -125,6 +125,7 @@ PASS_TO_BACKEND(update)
         return false;                         \
     }
 
+PASS_TO_BACKEND(valid)
 PASS_TO_BACKEND(released)
 PASS_TO_BACKEND(grabbed)
 
diff --git a/libraries/AP_Gripper/AP_Gripper.h b/libraries/AP_Gripper/AP_Gripper.h
index 68fb5792a7..fde973abf7 100644
--- a/libraries/AP_Gripper/AP_Gripper.h
+++ b/libraries/AP_Gripper/AP_Gripper.h
@@ -44,6 +44,9 @@ public:
     // update - should be called at at least 10hz
     void update();
 
+    // valid - returns true if we have a gripper and it should work
+    bool valid() const;
+
     static const struct AP_Param::GroupInfo        var_info[];
 
     // parameters
diff --git a/libraries/AP_Gripper/AP_Gripper_Backend.h b/libraries/AP_Gripper/AP_Gripper_Backend.h
index 868f4b9be4..06b68d51fb 100644
--- a/libraries/AP_Gripper/AP_Gripper_Backend.h
+++ b/libraries/AP_Gripper/AP_Gripper_Backend.h
@@ -34,6 +34,9 @@ public:
     // release - move the servo output to the release position
     virtual void release() = 0;
 
+    // valid - returns true if the backend should be working
+    bool valid() const { return true; };
+
     // released - returns true if currently in released position
     virtual bool released() const = 0;