diff --git a/hgdriver/hgdev/usb_manager.cpp b/hgdriver/hgdev/usb_manager.cpp
index e720ecf..d9f5c1f 100644
--- a/hgdriver/hgdev/usb_manager.cpp
+++ b/hgdriver/hgdev/usb_manager.cpp
@@ -73,7 +73,7 @@ int LIBUSB_CALL usb_manager::usb_pnp_callback(libusb_context* ctx, libusb_device
     usb_manager* obj = (usb_manager*)monitor;
 
 //    if (event == LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED)
-        libusb_ref_device(device);  // keep the object until handle it
+        //libusb_ref_device(device);  // keep the object until handle it
     //else if(event == LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT)
     //    libusb_unref_device(device);
 
@@ -190,17 +190,22 @@ void usb_manager::thread_notify_usb_event()
                 }
             }
 
+            libusb_ref_device(pd.dev);      // for re-enter the queue pnp_events_
             notify_usb_event(pd, &retry);
             if (retry)
             {
                 if(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now() - pd.happen_time).count()
                     <= 5000)
                     pnp_events_.Put(pd, sizeof(pd));
+                else
+                    retry = false;
                 if(pnp_events_.Size() == 1)
                     this_thread::sleep_for(chrono::milliseconds(1000));
                 else
                     this_thread::sleep_for(chrono::milliseconds(delay));
             }
+            if (!retry)
+                libusb_unref_device(pd.dev);
         }
     }
 }
@@ -295,6 +300,7 @@ int usb_manager::on_usb_pnp_event(libusb_context *ctx, libusb_device *device, li
     PNPDEV pd;
     unsigned ms = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now() - born_).count();
 
+    libusb_ref_device(device);
     pd.ctx = ctx;
     pd.dev = device;
     pd.event = event;
@@ -307,9 +313,12 @@ int usb_manager::on_usb_pnp_event(libusb_context *ctx, libusb_device *device, li
     else
     {
         bool retry = false;
+        libusb_ref_device(device);
         notify_usb_event(pd, &retry);
         if(retry)
             pnp_events_.Put(pd, sizeof(pd));
+        else
+            libusb_unref_device(device);
     }
 
     return 0;
@@ -779,6 +788,23 @@ void usb_io::init_after_open(void)
         close();
         last_err_ = err;
     }
+    else
+    {
+        libusb_device_descriptor    dd = { 0 };
+        char                        product[128] = { 0 };
+
+        if (libusb_get_device_descriptor(dev_info_.device, &dd) == LIBUSB_SUCCESS)
+        {
+            libusb_get_string_descriptor_ascii(handle_, dd.iProduct, (unsigned char*)product, _countof(product) - 1);
+            utils::to_log(LOG_LEVEL_DEBUG, "Product: %s\n", product);
+
+            char* v = strstr(product, "(V");
+            if (v)
+            {
+                ver_ = atoi(v + 2);
+            }
+        }
+    }
 }
 void usb_io::open(void)
 {
@@ -1113,6 +1139,10 @@ int usb_io::get_pid(void)
 {
     return dev_info_.pid;
 }
+int usb_io::get_ver(void)
+{
+    return ver_;
+}
 
 void usb_io::on_disconnected(void)
 {
diff --git a/hgdriver/hgdev/usb_manager.h b/hgdriver/hgdev/usb_manager.h
index ab04faf..1951794 100644
--- a/hgdriver/hgdev/usb_manager.h
+++ b/hgdriver/hgdev/usb_manager.h
@@ -153,6 +153,7 @@ class usb_io
     int                     last_err_;
     std::string             init_err_msg_;
     libusb_device           *ref_device_;
+    int                     ver_ = 1;
 
     // endpoint ports
     usb_manager::USBTRANSENDP  endpoints_;