Android: USB Communication Android <-> External Device

Question

I found several threads speacking about this subject, but after read them I don\'t have a clear idea about my problem.

We have a external device (something like a tomtom

Answer 1

Currently the adb interface is one way. Flow is controlled by the host PC using adb. Looking at your requirement, looks like you might need to open up the source code, re-tune the USB driver to allow communication both ways. After that, you will need to design your very own API that allows an application to send messages via USB. This will require a lot of work as the current Android model does not support it.