diff --git a/sample/cmux_sample_gsm.c b/sample/cmux_sample_gsm.c
index f24a398..db9cfa9 100644
--- a/sample/cmux_sample_gsm.c
+++ b/sample/cmux_sample_gsm.c
@@ -67,7 +67,7 @@ int cmux_sample(void)
     }
     LOG_I("cmux object channel (%s) attach successful.", CMUX_PPP_NAME);
 end:
-    return RT_EOK;
+    return result;
 }
 #ifdef CMUX_ATUO_INITIZATION
 INIT_APP_EXPORT(cmux_sample);
diff --git a/src/cmux.c b/src/cmux.c
index 5a35f10..d7645d5 100644
--- a/src/cmux.c
+++ b/src/cmux.c
@@ -77,7 +77,7 @@
 #endif
 #include <rtdbg.h>
 
-static rt_size_t cmux_send_data(struct rt_device *dev, int port, rt_uint8_t type, const char *data, int length);
+static rt_ssize_t cmux_send_data(struct rt_device *dev, int port, rt_uint8_t type, const char *data, int length);
 static rt_slist_t cmux_list = RT_SLIST_OBJECT_INIT(cmux_list);
 /* only one cmux object can be created */
 static struct cmux *_g_cmux = RT_NULL;
@@ -527,7 +527,7 @@ static void cmux_recv_processdata(struct cmux *cmux, rt_uint8_t *buf, rt_size_t
  *
  * @return  length
  */
-static rt_size_t cmux_send_data(struct rt_device *dev, int port, rt_uint8_t type, const char *data, int length)
+static rt_ssize_t cmux_send_data(struct rt_device *dev, int port, rt_uint8_t type, const char *data, int length)
 {
     /* flag, EA=1 C port, frame type, data_length 1-2 */
     rt_uint8_t prefix[5] = {CMUX_HEAD_FLAG, CMUX_ADDRESS_EA | CMUX_ADDRESS_CR, 0, 0, 0};
@@ -649,12 +649,13 @@ rt_err_t cmux_init(struct cmux *object, const char *name, rt_uint8_t vcom_num, v
 
     object->vcom_num = vcom_num;
     object->vcoms = rt_malloc(vcom_num * sizeof(struct cmux_vcoms));
-    rt_memset(object->vcoms, 0, vcom_num * sizeof(struct cmux_vcoms));
+    
     if (object->vcoms == RT_NULL)
     {
         LOG_E("cmux vcoms malloc failed.");
         return -RT_ENOMEM;
     }
+    rt_memset(object->vcoms, 0, vcom_num * sizeof(struct cmux_vcoms));
 
     object->buffer = cmux_buffer_init();
     if (object->buffer == RT_NULL)
@@ -830,14 +831,14 @@ static rt_err_t cmux_vcom_close(rt_device_t dev)
  *
  * @return  the result
  */
-static rt_size_t cmux_vcom_write(struct rt_device *dev,
+static rt_ssize_t cmux_vcom_write(struct rt_device *dev,
                                  rt_off_t pos,
                                  const void *buffer,
                                  rt_size_t size)
 {
     struct cmux *cmux = RT_NULL;
     struct cmux_vcoms *vcom = (struct cmux_vcoms *)dev;
-    rt_size_t len;
+    rt_ssize_t len;
     cmux = _g_cmux;
 
     /* use virtual serial, we can write data into actual serial directly. */
@@ -855,7 +856,7 @@ static rt_size_t cmux_vcom_write(struct rt_device *dev,
  *
  * @return  the result
  */
-static rt_size_t cmux_vcom_read(struct rt_device *dev,
+static rt_ssize_t cmux_vcom_read(struct rt_device *dev,
                                 rt_off_t pos,
                                 void *buffer,
                                 rt_size_t size)