diff --git a/Ubiquitous/XiZi/arch/arm/cortex-m23/pendsv.S b/Ubiquitous/XiZi/arch/arm/cortex-m23/pendsv.S
index 4fcd6ee24..1c1fe65dc 100644
--- a/Ubiquitous/XiZi/arch/arm/cortex-m23/pendsv.S
+++ b/Ubiquitous/XiZi/arch/arm/cortex-m23/pendsv.S
@@ -76,7 +76,6 @@ PendSV_Handler:
     MOV     R7, R11
     STMIA   R1!, {R4 - R7}          /* push thread {R8 - R11} high register to thread stack */
 switch_to_task:
-    BL       UpdateRunningTask
 
     LDR     R1, =InterruptToKtask
     LDR     R1, [R1]
diff --git a/Ubiquitous/XiZi/arch/arm/shared/pendsv.S b/Ubiquitous/XiZi/arch/arm/shared/pendsv.S
index 561778f77..3461f4808 100644
--- a/Ubiquitous/XiZi/arch/arm/shared/pendsv.S
+++ b/Ubiquitous/XiZi/arch/arm/shared/pendsv.S
@@ -70,9 +70,6 @@ PendSV_Handler:
 
 switch_to_task:
 
-    PUSH    {lr}
-    BL      UpdateRunningTask
-    POP     {lr}
 
 #ifdef TASK_ISOLATION
     PUSH    {lr}
diff --git a/Ubiquitous/XiZi/kernel/thread/CriticalArea.c b/Ubiquitous/XiZi/kernel/thread/CriticalArea.c
index f313e30e8..2cc850ec5 100644
--- a/Ubiquitous/XiZi/kernel/thread/CriticalArea.c
+++ b/Ubiquitous/XiZi/kernel/thread/CriticalArea.c
@@ -95,7 +95,7 @@ uint16 GetOsAssignLockLevel(void)
 
 #include <xs_hook.h>
 
-static int16 KTaskOsAssignLockNest;
+static uint16 KTaskOsAssignLockNest;
 
 /**
  * This function will get critical lock  level.
diff --git a/Ubiquitous/XiZi/kernel/thread/assign.c b/Ubiquitous/XiZi/kernel/thread/assign.c
index 2bef0fe53..776b61f6a 100644
--- a/Ubiquitous/XiZi/kernel/thread/assign.c
+++ b/Ubiquitous/XiZi/kernel/thread/assign.c
@@ -87,6 +87,7 @@ SWITCH:
 
         Assign.ready_vector_done->remove(new_task);
         KTaskStatSetAsRunning(new_task);
+        Assign.os_running_task = new_task;
 
         SYS_KDEBUG_LOG(KDBG_SCHED,
                 ("[%d]switch to priority#%d "
@@ -162,6 +163,7 @@ SWITCH:
 
         Assign.ready_vector_done->remove(new_task);
         KTaskStatSetAsRunning(new_task);
+        Assign.os_running_task = new_task;
 
         SYS_KDEBUG_LOG(KDBG_SCHED,
                 ("[%d]switch to priority#%d "
@@ -327,6 +329,7 @@ x_err_t YieldOsAssign(void)
 
         Assign.ready_vector_done->remove(new_task);
         KTaskStatSetAsRunning(new_task);
+        Assign.os_running_task = new_task;
 
         SYS_KDEBUG_LOG(KDBG_SCHED,
                 ("[%d]switch to priority#%d "
diff --git a/Ubiquitous/XiZi/tool/shell/letter-shell/shell.c b/Ubiquitous/XiZi/tool/shell/letter-shell/shell.c
index 6a923ece8..201178a12 100644
--- a/Ubiquitous/XiZi/tool/shell/letter-shell/shell.c
+++ b/Ubiquitous/XiZi/tool/shell/letter-shell/shell.c
@@ -1647,9 +1647,17 @@ void shellTask(void *param)
     while(RET_TRUE)
     {
         if (shell->read) {
+            memset(data, 0, KEY_LENGTH);
+            data_len = 0;
+            x_base lock;
+
             data_len = shell->read(data);
-            for (i = 0; i < data_len; i++) {
-                shellHandler(shell, data[i]);
+            if(data_len > 0) {
+                int lock = CriticalAreaLock();
+                for (i = 0; i < data_len; i++) {
+                    shellHandler(shell, data[i]);
+                }
+                CriticalAreaUnLock(lock);
             }
         }
     }
diff --git a/Ubiquitous/XiZi/tool/shell/letter-shell/shell_port.c b/Ubiquitous/XiZi/tool/shell/letter-shell/shell_port.c
index 661cfb604..8f315ebdd 100644
--- a/Ubiquitous/XiZi/tool/shell/letter-shell/shell_port.c
+++ b/Ubiquitous/XiZi/tool/shell/letter-shell/shell_port.c
@@ -48,10 +48,13 @@ signed char userShellRead(char *data)
 {
     char read_length = 0;
     struct BusBlockReadParam read_param;
-    read_param.read_length = 0;
-    read_param.size = 1;
-    read_param.buffer = data;
 
+    memset(&read_param,0, sizeof(read_param));
+
+    read_param.read_length = 0;
+    read_param.size = KEY_LENGTH;
+    read_param.buffer = data;
+    
     BusDevReadData(console, &read_param);
 
     read_length = (char)read_param.read_length;
@@ -120,7 +123,7 @@ int userShellInit(void)
     tid = KTaskCreate("letter-shell",
                            shellTask, &shell,
                            SHELL_TASK_STACK_SIZE, SHELL_TASK_PRIORITY);
-        
+
         StartupKTask(tid);
         return 0;
 }