https://qooah.com/2011/01/09/viewsonic-%e5%8a%a0%e5%85%a5%e6%88%b0%e5%9c%98%ef%b9%97%e9%a6%96%e9%83%a8-android-%e6%99%ba%e8%83%bd%e6%89%8b%e6%a9%9f-viewpad-4/