usb許可權問題解決辦法：
http://stackoverflow.com/questions/11183792/android-usb-host-and-hidden-devices
  create  file:
/system/etc/permissions/android.hardware.usb.host.xml                   
 
<permissions>
 <feature name="android.hardware.usb.host"/>
</permissions>
 
&&  find the file in same folder
   handheld_core_hardware.xml  
or  
   tablet_core_hardware.xml
 
and add  
<feature name="android.hardware.usb.host">
into  <permissions> section