AP_Arming: add accessor to retrieve last disarm method

libraries/AP_Arming/AP_Arming.cpp

@@ -1171,6 +1171,7 @@ bool AP_Arming::disarm(const AP_Arming::Method method)
         return false;
     }
     armed = false;
+    _last_disarm_method = method;
 
     Log_Write_Disarm(method); // should be able to pass through force here?
 

libraries/AP_Arming/AP_Arming.h

@@ -72,6 +72,7 @@ public:
         PILOT_INPUT_FAILSAFE = 29, // only disarm uses this...
         TOYMODELANDTHROTTLE = 30, // only disarm uses this...
         TOYMODELANDFORCE = 31, // only disarm uses this...
+        UNKNOWN = 100,
     };
 
     enum class Required {
@@ -118,6 +119,10 @@ public:
 
     static const struct AP_Param::GroupInfo        var_info[];
 
+    // method that was last used for disarm; invalid unless the
+    // vehicle has been disarmed at least once.
+    Method last_disarm_method() const { return _last_disarm_method; } 
+
 protected:
 
     // Parameters
@@ -224,6 +229,10 @@ private:
     char* aux_auth_fail_msg;    // buffer for holding failure messages
     bool aux_auth_error;        // true if too many auxiliary authorisers
     HAL_Semaphore aux_auth_sem; // semaphore for accessing the aux_auth_state and aux_auth_fail_msg
+
+    // method that was last used for disarm; invalid unless the
+    // vehicle has been disarmed at least once.
+    Method _last_disarm_method = Method::UNKNOWN;
 };
 
 namespace AP {