diff --git a/src/xtimer.rs b/src/xtimer.rs
index f81d9a3..0cb320b 100644
--- a/src/xtimer.rs
+++ b/src/xtimer.rs
@@ -244,6 +244,45 @@ impl XTimer {
         return ((self.timer_tick as usize) >> (TVR_BITS + index * TVN_BITS)) & TVN_MASK;
     }
 
+    fn fetch_work_list(&self, tick: i64) -> bool {
+        return true;
+    }
+
+    pub fn update(this: &Rc::<RefCell::<XTimer>>) {
+        let tick = (*this.borrow().get_tick_count.as_ref().unwrap())();
+        let work_list = this.borrow().work_list.clone();
+        while this.borrow().fetch_work_list(tick) {
+            while !work_list.borrow().empty() {
+                let timer = &work_list.borrow().first_entry();
+                this.borrow_mut().running_timer = timer.clone();
+                match &mut timer.upgrade().unwrap().borrow_mut().cb {
+                    Some(v) => {
+                        (*v)(TimerEvent::Exec, None);
+                    }
+                    None => {
+                    }
+                }
+                match this.borrow().running_timer.upgrade() {
+                    Some(v) => {
+                        match v.borrow().timer_type {
+                            TimerType::Timeout => {
+                                this.borrow_mut().internal_delete(Rc::downgrade(&v.borrow().wp.clone().unwrap()), false);
+                            }
+                            TimerType::Interval => {
+                                this.borrow_mut().modify(Rc::downgrade(&v.borrow().wp.clone().unwrap()),
+                                            v.borrow().expire_time);
+                            }
+                        }
+                    }
+                    None => {
+                    }
+                }
+            }
+        }
+        this.borrow_mut().running_timer = Weak::new();
+    }
+
+    /*
     pub fn update(&mut self) {
         let tick = (*self.get_tick_count.as_ref().unwrap())();
         while tick >= self.timer_tick {
@@ -290,7 +329,7 @@ impl XTimer {
             }
         }
         self.running_timer = Weak::new();
-    }
+    }*/
 
     fn internal_add(&mut self,
                     timer_type: TimerType,