AP_Mission: added last_change_time_ms() call

will be used by terrain lib for scanning waypoints

libraries/AP_Mission/AP_Mission.cpp

@@ -42,6 +42,8 @@ void AP_Mission::init()
     if (sizeof(union Content) != 12) {
         hal.scheduler->panic(PSTR("AP_Mission Content must be 12 bytes"));
     }
+
+    _last_change_time_ms = hal.scheduler->millis();
 }
 
 /// start - resets current commands to point to the beginning of the mission
@@ -423,6 +425,9 @@ bool AP_Mission::write_cmd_to_storage(uint16_t index, Mission_Command& cmd)
     hal.storage->write_word(pos_in_storage+1, cmd.p1);
     hal.storage->write_block(pos_in_storage+3, cmd.content.bytes, 12);
 
+    // remember when the mission last changed
+    _last_change_time_ms = hal.scheduler->millis();
+
     // return success
     return true;
 }

libraries/AP_Mission/AP_Mission.h

@@ -189,7 +189,8 @@ public:
         _cmd_start_fn(cmd_start_fn),
         _cmd_verify_fn(cmd_verify_fn),
         _mission_complete_fn(mission_complete_fn),
-        _prev_nav_cmd_index(AP_MISSION_CMD_INDEX_NONE)
+        _prev_nav_cmd_index(AP_MISSION_CMD_INDEX_NONE),
+        _last_change_time_ms(0)
     {
         // load parameter defaults
         AP_Param::setup_object_defaults(this, var_info);
@@ -320,6 +321,9 @@ public:
     //  return true on success, false on failure
     static bool mission_cmd_to_mavlink(const AP_Mission::Mission_Command& cmd, mavlink_mission_item_t& packet);
 
+    // return the last time the mission changed in milliseconds
+    uint32_t last_change_time_ms(void) const { return _last_change_time_ms; }
+
     // user settable parameters
     static const struct AP_Param::GroupInfo var_info[];
 
@@ -403,6 +407,9 @@ private:
         uint16_t index;                 // index of do-jump commands in mission
         int16_t num_times_run;          // number of times this jump command has been run
     } _jump_tracking[AP_MISSION_MAX_NUM_DO_JUMP_COMMANDS];
+
+    // last time that mission changed
+    uint32_t _last_change_time_ms;
 };
 
 #endif