diff --git a/trunk/bootrom/build/libraries/os/common/os_alarm.c b/trunk/bootrom/build/libraries/os/common/os_alarm.c
index 2f37fcb..99cc1a0 100644
--- a/trunk/bootrom/build/libraries/os/common/os_alarm.c
+++ b/trunk/bootrom/build/libraries/os/common/os_alarm.c
@@ -104,7 +104,7 @@ static void i_osSetTimer(OSAlarm *alarm)
 //osPrintf( "**i_osSetTimer  alarm=%x, fire=%llx  time=%llx delta=%lld timeCount=%x \n", alarm, alarm->fire, time, delta, (int)timerCount );
 
 #ifdef SDK_ARM11
-    osStartTimer(OSi_ALARM_TIMER, timerCount, 0);
+    osStartTimer(OSi_ALARM_TIMER, timerCount, OS_TICK_PRESCALE);
 #else // SDK_ARM9
     osSetTimerCount((OSTimer)OSi_ALARM_TIMER, timerCount);
     osSetTimerControl(OSi_ALARM_TIMER, (u16)OSi_ALARM_TIMERCONTROL);
diff --git a/trunk/bootrom/build/libraries/os/common/os_tick.c b/trunk/bootrom/build/libraries/os/common/os_tick.c
index ae881ac..896efcc 100644
--- a/trunk/bootrom/build/libraries/os/common/os_tick.c
+++ b/trunk/bootrom/build/libraries/os/common/os_tick.c
@@ -73,7 +73,7 @@ void osInitTick(void)
 #ifdef SDK_ARM11
         osStopTimer(OSi_TICK_TIMER);
         osEnableTimerReload(OSi_TICK_TIMER);
-        osStartTimer(OSi_TICK_TIMER, OS_TICK_LO_LIMIT, 0);
+        osStartTimer(OSi_TICK_TIMER, OS_TICK_LO_LIMIT, OS_TICK_PRESCALE);
 #else // SDK_ARM9
         //---- setting timer
         osSetTimerControl(OSi_TICK_TIMER, 0);
@@ -130,7 +130,7 @@ static void i_osCountUpTick(void)
     {
 #ifdef SDK_ARM11
         osStopTimer(OSi_TICK_TIMER);
-        osStartTimer(OSi_TICK_TIMER, OS_TICK_LO_LIMIT, 0);
+        osStartTimer(OSi_TICK_TIMER, OS_TICK_LO_LIMIT, OS_TICK_PRESCALE);
 #else // SDK_ARM9
         osSetTimerControl(OSi_TICK_TIMER, 0);
 #ifdef OS_TICK_USE_2TIMERS
@@ -258,7 +258,7 @@ void i_osSetTick(u64 count)
     osStopTimer(OSi_TICK_TIMER);
     osClearInterruptPendingID(OSi_TICK_IE_TIMER_ID);
 
-    osStartTimer(OSi_TICK_TIMER, (u32)(count & OS_TICK_LO_MASK), 0);
+    osStartTimer(OSi_TICK_TIMER, (u32)(count & OS_TICK_LO_MASK), OS_TICK_PRESCALE);
 
 #else // SDK_ARM9
     osSetTimerControl(OSi_TICK_TIMER, 0);
diff --git a/trunk/bootrom/build/libraries/os/common/os_timer.c b/trunk/bootrom/build/libraries/os/common/os_timer.c
index fb50eb2..16648ff 100644
--- a/trunk/bootrom/build/libraries/os/common/os_timer.c
+++ b/trunk/bootrom/build/libraries/os/common/os_timer.c
@@ -138,9 +138,16 @@ void i_osUnsetTimerReserved( int timer_id )
 void osStartTimer( OSTimer id, OSTimerCount count, OSTimerPrescaler preScale )
 {
     SDK_ASSERT(OS_TIMER_0 <= id && id < OS_TIMER_NUM);
+    SDK_ASSERT(2 <= preScale && preScale <= (256*2));
     //---- check if system reserved
     SDK_ASSERT(!i_osIsTimerReserved(id));
 
+    preScale /= 2;
+    if ( preScale )
+    {
+        preScale--;
+    }
+
     osSetTimerCount(id, count);
     osSetTimerControl(id, REG_OS_TM_CNT_E_MASK | REG_OS_TM_CNT_IT_MASK |
                           i_osTimerControl[id] |