diff --git a/libsigrok4DSL/backend.c b/libsigrok4DSL/backend.c
index 46dc8042..5f5714af 100644
--- a/libsigrok4DSL/backend.c
+++ b/libsigrok4DSL/backend.c
@@ -23,6 +23,9 @@
 #include "config.h" /* Needed for HAVE_LIBUSB_1_0 and others. */
 #include "log.h"
 
+#undef LOG_PREFIX 
+#define LOG_PREFIX "backend: "
+
 /**
  * @mainpage libsigrok API
  *
@@ -83,8 +86,8 @@
  * called, which will (among other things) free the struct sr_context.
  *
  * Example for a minimal program using libsigrok:
- *
- 
+ */
+
 
 /**
  * Sanity-check all libsigrok drivers.
@@ -331,12 +334,9 @@ SR_API int sr_init(struct sr_context **ctx)
 
 	context->libusb_ctx = NULL;
 	context->hotplug_handle = 0;
-	context->hotplug_callback = NULL;
-	context->hotplug_user_data = NULL;
+    context->hotplug_callback = NULL;
 	context->hotplug_tv.tv_sec = 0;
-	context->hotplug_tv.tv_usec = 0;
-	context->event_callback = NULL;
-	context->deiveList = NULL;
+    context->hotplug_tv.tv_usec = 0;
 
 	ret = libusb_init(&context->libusb_ctx);
 	if (LIBUSB_SUCCESS != ret) {
@@ -386,7 +386,7 @@ LIBUSB_CALL int sr_hotplug_callback(struct libusb_context *ctx, struct libusb_de
                                   libusb_hotplug_event event, void *user_data){
 
 	  if (user_data == NULL){
-		  sr_err("%s(): libsigrok usb event callback, userdata is NULL.", __func__);
+		 sr_err("%s(): libsigrok usb event callback, userdata is NULL.", __func__);
 		 return 0;
 	  }
 
@@ -398,13 +398,13 @@ LIBUSB_CALL int sr_hotplug_callback(struct libusb_context *ctx, struct libusb_de
 
       struct sr_context *user_ctx = (struct sr_context*)user_data;
 	  if (user_ctx->hotplug_callback != NULL){
-		  user_ctx->hotplug_callback(ctx, dev, ev, user_ctx->hotplug_user_data);
+		  user_ctx->hotplug_callback(ctx, dev, ev);
 	  }
 
 	  return 0;
 }
 
-SR_API int sr_listen_hotplug(struct sr_context *ctx, hotplug_event_callback callback, void *userdata)
+SR_PRIV int sr_listen_hotplug(struct sr_context *ctx, hotplug_event_callback callback)
 {
 	int ret;
 
@@ -416,9 +416,9 @@ SR_API int sr_listen_hotplug(struct sr_context *ctx, hotplug_event_callback call
 		sr_err("%s(): callback was NULL.", __func__);
 		return SR_ERR;		
 	}
+	sr_info("%s", "Register hotplug callback.");
 
 	ctx->hotplug_callback = callback;
-	ctx->hotplug_user_data = userdata;
 
     ret = libusb_hotplug_register_callback(ctx->libusb_ctx,
                                            (libusb_hotplug_event)(LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED | LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT),
@@ -427,7 +427,7 @@ SR_API int sr_listen_hotplug(struct sr_context *ctx, hotplug_event_callback call
                                            LIBUSB_HOTPLUG_MATCH_ANY,
                                            LIBUSB_HOTPLUG_MATCH_ANY, 
                                            (libusb_hotplug_callback_fn)sr_hotplug_callback,
-                                           ctx,
+                                           ctx, //user data
                                            &ctx->hotplug_handle);
     if (LIBUSB_SUCCESS != ret){
        return -1;
@@ -436,25 +436,25 @@ SR_API int sr_listen_hotplug(struct sr_context *ctx, hotplug_event_callback call
 	return 0;
 }
 
-SR_API int sr_close_hotplug(struct sr_context *ctx)
+SR_PRIV int sr_close_hotplug(struct sr_context *ctx)
 {
 	if (!ctx) {
 		sr_err("%s(): libsigrok context was NULL.", __func__);
 		return SR_ERR;
 	}
-
+	sr_info("%s", "Unregister hotplug callback.");
 	libusb_hotplug_deregister_callback(ctx->libusb_ctx, ctx->hotplug_handle);
 
 	return 0;
 }
 
-SR_API void sr_hotplug_wait_timout(struct sr_context *ctx)
+SR_PRIV void sr_hotplug_wait_timout(struct sr_context *ctx)
 {
 	if (!ctx) {
 		sr_err("%s(): libsigrok context was NULL.", __func__);
 		return;
-	}
-	 libusb_handle_events_timeout(ctx->libusb_ctx, &ctx->hotplug_tv);
+	} 
+	libusb_handle_events_timeout(ctx->libusb_ctx, &ctx->hotplug_tv);
 }
 
 /** @} */
diff --git a/libsigrok4DSL/hardware/DSL/dscope.c b/libsigrok4DSL/hardware/DSL/dscope.c
index c6a6d605..69e86c7f 100644
--- a/libsigrok4DSL/hardware/DSL/dscope.c
+++ b/libsigrok4DSL/hardware/DSL/dscope.c
@@ -308,7 +308,7 @@ static GSList *scan(GSList *options)
 		}
         else {
             char *firmware;
-            char *res_path = sr_get_firmware_res_path();
+            char *res_path = DS_RES_PATH;
             if (!(firmware = g_try_malloc(strlen(res_path)+strlen(prof->firmware)+1))) {
                 sr_err("Firmware path malloc error!");
                 return NULL;
diff --git a/libsigrok4DSL/hardware/DSL/dsl.c b/libsigrok4DSL/hardware/DSL/dsl.c
index e51e967d..27ad43fc 100644
--- a/libsigrok4DSL/hardware/DSL/dsl.c
+++ b/libsigrok4DSL/hardware/DSL/dsl.c
@@ -1919,7 +1919,7 @@ SR_PRIV int dsl_dev_open(struct sr_dev_driver *di, struct sr_dev_inst *sdi, gboo
     if (sdi->status == SR_ST_ACTIVE) {
         if (!(*fpga_done)) {
             char *fpga_bit;
-            char *res_path = sr_get_firmware_res_path();
+            char *res_path = DS_RES_PATH;
             if (!(fpga_bit = g_try_malloc(strlen(res_path)+strlen(devc->profile->fpga_bit33)+1))) {
                 sr_err("fpag_bit path malloc error!");
                 return SR_ERR_MALLOC;
diff --git a/libsigrok4DSL/hardware/DSL/dslogic.c b/libsigrok4DSL/hardware/DSL/dslogic.c
index 709f323a..1ec18d8b 100644
--- a/libsigrok4DSL/hardware/DSL/dslogic.c
+++ b/libsigrok4DSL/hardware/DSL/dslogic.c
@@ -379,7 +379,7 @@ static GSList *scan(GSList *options)
 		}
         else {
             char *firmware;
-            char *res_path = sr_get_firmware_res_path();
+            char *res_path = DS_RES_PATH;
             if (!(firmware = g_try_malloc(strlen(res_path)+strlen(prof->firmware)+1))) {
                 sr_err("Firmware path malloc error!");
                 return NULL;
@@ -1008,7 +1008,7 @@ static int config_set(int id, GVariant *data, struct sr_dev_inst *sdi,
                     ret = SR_ERR;
                 }
                 char *fpga_bit;
-                char *res_path = sr_get_firmware_res_path();
+                char *res_path = DS_RES_PATH;
                 if (!(fpga_bit = g_try_malloc(strlen(res_path)+strlen(devc->profile->fpga_bit33)+1))) {
                     sr_err("fpag_bit path malloc error!");
                     return SR_ERR_MALLOC;
diff --git a/libsigrok4DSL/lib_main.c b/libsigrok4DSL/lib_main.c
index 88a4fc7f..c87b20cc 100644
--- a/libsigrok4DSL/lib_main.c
+++ b/libsigrok4DSL/lib_main.c
@@ -22,55 +22,68 @@
 #include "libsigrok-internal.h"
 #include "log.h"
 
-struct device_all_info
-{
-	struct sr_device_info _base_info;
-};
+#ifdef _WIN32
+  #include <windows.h>
+  #define _sleep(m) Sleep((m))
+#else
+  #include <unistd.h>
+  #define _sleep(m) usleep((m) * 1000)
+#endif
 
-#define SR_DEVICE_MAX_COUNT 100
+#undef LOG_PREFIX 
+#define LOG_PREFIX "lib_main: "
 
-static char DS_RES_PATH[500] = {0}; 
-static struct sr_context *g_sr_ctx = NULL;
+char DS_RES_PATH[500] = {0}; 
+static struct sr_context *sr_ctx = NULL;
+static libsigrok_event_callback_t event_callback = NULL;
+static GList*	all_device_list = NULL; // All device instance, sr_dev_inst* type
+static GThread	*hotplug_thread = NULL;
+
+static int sr_exit_flag = 0;
+static int attach_event_flag = 0;
+static int detach_event_flag = 0;
+static int wait_redo_attch_flag = 0;
+static int wait_redo_attch_times = 0;
  
- //----------------------------private function----------------
-
- /**
-  * Free device resource
- */
- static sr_free_device(struct device_all_info *dev)
- {
-	if (dev){
-		free(dev);
-	}
- }
+static void hotplug_event_listen_callback(struct libusb_context *ctx, struct libusb_device *dev, int event);
+static void usb_hotplug_process_proc();
 
 /**
  * Must call first
  */
 SR_API int sr_lib_init()
-{
+{ 
 	int ret = 0;
 	struct sr_dev_driver **drivers = NULL;
 	struct sr_dev_driver **dr = NULL;
 
-	if (g_sr_ctx != NULL){
+	if (sr_ctx != NULL){
 		return SR_ERR_HAVE_DONE;
 	}
 
-	ret = sr_init(&g_sr_ctx);
+	ret = sr_init(&sr_ctx);
     if (ret != SR_OK){
 		return ret;
 	}
+	sr_exit_flag = 0;
 
 	// Initialise all libsigrok drivers
 	drivers = sr_driver_list();
 	for (dr = drivers; *dr; dr++) {
-		if (sr_driver_init(g_sr_ctx, *dr) != SR_OK) {
+		if (sr_driver_init(sr_ctx, *dr) != SR_OK) {
 			sr_err("Failed to initialize driver '%s'", (*dr)->name);
 			return SR_ERR;
 		}
 	}
 
+	sr_ctx->hotplug_tv.tv_sec = 0;
+    sr_ctx->hotplug_tv.tv_usec = 0;
+
+	sr_listen_hotplug(sr_ctx, hotplug_event_listen_callback);
+
+	/** Start usb hotplug thread */
+	hotplug_thread = g_thread_new("hotplug_proc", usb_hotplug_process_proc, NULL);
+
 	return SR_OK;
 }
 
@@ -84,13 +97,22 @@ SR_API int sr_lib_exit()
 	struct sr_dev_driver *driver_ins;
 	GSList *l;
 	struct sr_dev_inst *dev;
-  
-	if (g_sr_ctx == NULL){
+ 
+	if (sr_ctx == NULL){
 		return SR_ERR_HAVE_DONE;
 	}
 
+	sr_close_hotplug(sr_ctx);
+
+	sr_exit_flag = 1; //all thread to exit
+
+	if (hotplug_thread != NULL){
+		g_thread_join(hotplug_thread);
+		hotplug_thread = NULL;
+	}
+
 	// Release all device
-	for (l=g_sr_ctx->deiveList; l; l = l->next)
+	for (l = all_device_list; l; l = l->next)
 	{
 		dev = l->data;
 		if (dev && dev->driver)
@@ -103,12 +125,13 @@ SR_API int sr_lib_exit()
 				driver_ins->dev_close(dev);
 		}
 	}
-	g_safe_free_list(g_sr_ctx->deiveList);
+	g_safe_free_list(all_device_list);
+    
 
-	if (sr_exit(g_sr_ctx) != SR_OK){
+	if (sr_exit(sr_ctx) != SR_OK){
 		sr_err("%s", "call sr_exit error");
 	}
-    g_sr_ctx = NULL;
+    sr_ctx = NULL;
 
     return SR_OK;
 }
@@ -129,21 +152,84 @@ SR_API void sr_set_firmware_resource_dir(const char *dir)
 	}
 }
 
-SR_PRIV char* sr_get_firmware_res_path()
-{
-	return DS_RES_PATH;
-}
-
 /**
  * Set event callback, event type see enum libsigrok_event_type
  */
 SR_API void sr_set_event_callback(libsigrok_event_callback_t *cb)
 {
-    if (g_sr_ctx == NULL)
-		sr_lib_init();
-	
-	if (g_sr_ctx != NULL){
-		g_sr_ctx->event_callback = cb;
+	event_callback = cb;
+}
+
+
+/**-------------------private function ---------------*/
+
+static int scan_hardware_device()
+{
+
+}
+
+static void hotplug_event_listen_callback(struct libusb_context *ctx, struct libusb_device *dev, int event)
+{
+	if (event == USB_EV_HOTPLUG_ATTACH){
+		sr_info("One device attached.");
+
+		if (wait_redo_attch_flag){
+			sr_info("%s", "Device loose contact, but it reconnect success.");
+		}
+		wait_redo_attch_flag = 0;
+		attach_event_flag = 1;
+	}
+	else if (event == USB_EV_HOTPLUG_DETTACH){
+		sr_info("One device detached.");
+		wait_redo_attch_flag = 1;  //Begin wait the device reconnect, if timeout, will process the detach event.
+		wait_redo_attch_times = 0;
+	}
+	else{
+		sr_err("%s", "Unknown usb event");
+		wait_redo_attch_flag = 1;
 	}
 }
 
+static void process_attach_event()
+{
+	sr_info("%s", "Process device attch event.");
+}
+
+static void process_detach_event()
+{
+	sr_info("%s", "Process device detach event.");
+}
+
+static void usb_hotplug_process_proc()
+{
+	sr_info("%s", "Hotplug thread start!");
+
+	while (!sr_exit_flag)
+	{
+		sr_hotplug_wait_timout(sr_ctx);
+
+		if (attach_event_flag){
+			process_attach_event();
+			attach_event_flag = 0;
+		}
+		if (detach_event_flag){
+			process_detach_event();
+			detach_event_flag = 0;
+		}
+
+		_sleep(100);
+
+		if (wait_redo_attch_flag){
+			wait_redo_attch_times++;
+
+			// 500ms
+			if (wait_redo_attch_times == 5){
+				//Device loose contact,wait for it reconnection timeout.
+				detach_event_flag = 1; // use detach event
+				wait_redo_attch_flag = 0;
+			}              
+		}
+	}
+	
+	sr_info("%s", "Hotplug thread end!");
+}
\ No newline at end of file
diff --git a/libsigrok4DSL/libsigrok-internal.h b/libsigrok4DSL/libsigrok-internal.h
index 7670f4b5..805e77e8 100644
--- a/libsigrok4DSL/libsigrok-internal.h
+++ b/libsigrok4DSL/libsigrok-internal.h
@@ -48,17 +48,23 @@
 #undef max
 #define max(a,b) ((a)>(b)?(a):(b))
 
+#define USB_EV_HOTPLUG_UNKNOW		0
+#define USB_EV_HOTPLUG_ATTACH		1
+#define USB_EV_HOTPLUG_DETTACH		2
+
 #define g_safe_free(p) 			if((p)) g_free((p)); ((p)) = NULL;
 #define g_safe_free_list(p) 	if((p)) g_slist_free((p)); ((p)) = NULL;
 
+/** global variable */
+extern char DS_RES_PATH[500];
+
+typedef void (*hotplug_event_callback)(struct libusb_context *ctx, struct libusb_device *dev, int event);
+
 struct sr_context {
 	libusb_context*			libusb_ctx;
 	libusb_hotplug_callback_handle hotplug_handle;
 	hotplug_event_callback  hotplug_callback;
-	void 					*hotplug_user_data;
 	struct 					timeval hotplug_tv;
-	libsigrok_event_callback_t event_callback;
-	GList 					*deiveList; // All device instance, sr_dev_inst* type
 };
 
 struct sr_session {
@@ -182,6 +188,7 @@ SR_PRIV int sr_session_source_add_channel(GIOChannel *channel, int events,
 SR_PRIV int sr_session_source_remove(int fd);
 SR_PRIV int sr_session_source_remove_pollfd(GPollFD *pollfd);
 SR_PRIV int sr_session_source_remove_channel(GIOChannel *channel);
+SR_PRIV int sr_session_datafeed_callback_add(sr_datafeed_callback_t cb,void *cb_data);
 
 /*--- std.c -----------------------------------------------------------------*/
 
@@ -259,7 +266,10 @@ SR_PRIV int sr_usb_open(libusb_context *usb_ctx, struct sr_usb_dev_inst *usb);
 SR_PRIV int sr_init(struct sr_context **ctx);
 SR_PRIV int sr_exit(struct sr_context *ctx);
 
-/*--- lib_main.c -------------------------------------------------*/
-SR_PRIV char* sr_get_firmware_res_path();
+SR_PRIV int sr_listen_hotplug(struct sr_context *ctx, hotplug_event_callback callback);
+SR_PRIV int sr_close_hotplug(struct sr_context *ctx);
+SR_PRIV void sr_hotplug_wait_timout(struct sr_context *ctx);
 
+/*--- lib_main.c -------------------------------------------------*/
+ 
 #endif
diff --git a/libsigrok4DSL/libsigrok.h b/libsigrok4DSL/libsigrok.h
index de793a93..1f98cbde 100644
--- a/libsigrok4DSL/libsigrok.h
+++ b/libsigrok4DSL/libsigrok.h
@@ -160,11 +160,6 @@ enum {
 #define SR_PRIV
 #endif
 
-
-#define USB_EV_HOTPLUG_UNKNOW		0
-#define USB_EV_HOTPLUG_ATTACH		1
-#define USB_EV_HOTPLUG_DETTACH		2
-
 typedef unsigned long long sr_device_handle;
 
 enum sr_device_type{
@@ -1263,11 +1258,6 @@ struct ds_trigger_pos {
 /*--- backend.c -------------------------------------------------------------*/
 
 //@event, 1:attach, 2:left
-typedef void (*hotplug_event_callback)(void *context,void *device, int event, void *userdata);
-SR_API int sr_listen_hotplug(struct sr_context *ctx, hotplug_event_callback callback, void *userdata);
-SR_API int sr_close_hotplug(struct sr_context *ctx);
-SR_API void sr_hotplug_wait_timout(struct sr_context *ctx);
-
 SR_PRIV int sr_init(struct sr_context **ctx);
 SR_PRIV int sr_exit(struct sr_context *ctx);
 
@@ -1327,8 +1317,7 @@ SR_API int sr_session_dev_list(GSList **devlist);
 
 /* Datafeed setup */
 SR_API int sr_session_datafeed_callback_remove_all(void);
-SR_API int sr_session_datafeed_callback_add(sr_datafeed_callback_t cb,
-		void *cb_data);
+
 
 /* Session control */
 SR_API int sr_session_start(void);
@@ -1478,7 +1467,7 @@ SR_API void sr_set_firmware_resource_dir(const char *dir);
 
 /**
  * Get the device list, the last item is null.
- * Call free to release buffer. If the list is empty, it returns null.
+ * User need call free() to release the buffer. If the list is empty, it returns null.
  */
 SR_API struct sr_device_info* sr_device_get_list(int *out_count);
 
@@ -1488,6 +1477,13 @@ SR_API struct sr_device_info* sr_device_get_list(int *out_count);
  */
 SR_API int sr_device_select(sr_device_handle handle);
 
+/**
+ * Active a device, if success, it will trigs the event of EV_CURRENT_DEVICE_CHANGED.
+ * If the old actived device is hardware, maybe user need store the data first.
+ * @index is -1, will select the last one.
+ */
+SR_API int sr_device_select_by_index(int index);
+
 /**
  * Create a device from session file, it auto load the data.
  */
diff --git a/libsigrok4DSL/session.c b/libsigrok4DSL/session.c
index 1db07e78..e029bf47 100644
--- a/libsigrok4DSL/session.c
+++ b/libsigrok4DSL/session.c
@@ -253,7 +253,7 @@ SR_API int sr_session_datafeed_callback_remove_all(void)
  *
  * @return SR_OK upon success, SR_ERR_BUG if no session exists.
  */
-SR_API int sr_session_datafeed_callback_add(sr_datafeed_callback_t cb, void *cb_data)
+SR_PRIV int sr_session_datafeed_callback_add(sr_datafeed_callback_t cb, void *cb_data)
 {
 	struct datafeed_callback *cb_struct;
 
diff --git a/libsigrok4DSL/tests/test_main.c b/libsigrok4DSL/tests/test_main.c
index 4cac2eaf..1eea2d85 100644
--- a/libsigrok4DSL/tests/test_main.c
+++ b/libsigrok4DSL/tests/test_main.c
@@ -1,8 +1,34 @@
 
 #include <libsigrok.h>
+#include "../log.h"
+#include <stdio.h>
 
-int main2()
+#undef LOG_PREFIX 
+#define LOG_PREFIX "test_main: "
+
+int main()
 {
+    int ret = 0;
+
+    if ((ret = sr_lib_init()) != SR_OK)
+    {
+        return 0;
+    }   
+    sr_info("%s", "start.");
+
+    char c = 0;
+
+    while (1)
+    {
+       c = getchar();
+
+       if (c == 'x'){
+         sr_lib_exit();
+         sr_info("%s", "exit.");
+         break;
+       }
+    }
+    
 
     return 0;
 }
\ No newline at end of file