fix the next timeout issue in soft timer

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2484 bbd45198-f89e-11dd-88c7-29a3b14d5316

src/timer.c

@@ -17,6 +17,7 @@
  * 2009-11-11     LiJin        add soft timer
  * 2010-05-12     Bernard      fix the timer check bug.
  * 2010-11-02     Charlie      re-implement tick overflow issue
+ * 2012-12-15     Bernard      fix the next timeout issue in soft timer
  */
 
 #include <rtthread.h>
@@ -26,6 +27,14 @@
 static rt_list_t rt_timer_list = RT_LIST_OBJECT_INIT(rt_timer_list);
 
 #ifdef RT_USING_TIMER_SOFT
+#ifndef RT_TIMER_THREAD_STACK_SIZE
+#define RT_TIMER_THREAD_STACK_SIZE 512
+#endif
+
+#ifndef RT_TIMER_THREAD_PRIO
+#define RT_TIMER_THREAD_PRIO        0
+#endif
+
 /* soft timer list */
 static rt_list_t rt_soft_timer_list;
 static struct rt_thread timer_thread;
@@ -506,16 +515,28 @@ static void rt_thread_timer_entry(void *parameter)
     
     while (1)
     {
+        /* get the next timeout tick */
         next_timeout = rt_timer_list_next_timeout(&rt_soft_timer_list);
         if (next_timeout == RT_TICK_MAX)
         {
+            /* no software timer exist, suspend self. */
             rt_thread_suspend(rt_thread_self());
             rt_schedule();
         }
         else
         {
+            rt_tick_t current_tick;
+
+            /* get current tick */
+            current_tick = rt_tick_get();
+
+            if ((next_timeout - current_tick) < RT_TICK_MAX/2)
+            {
+                /* get the delta timeout tick */
+                next_timeout = next_timeout - current_tick;
                 rt_thread_delay(next_timeout);
             }
+        }
 
         /* lock scheduler */
         rt_enter_critical();