Purpose
-------

This project illustrates the problem faced when using libusb on Android. There
is permission issue for usage of USB on android. Besides static permission in
the Manifest, android requires the application to ask permission for usage of
USB device at runtime.

The error that is seen is:
I stderr  : libusb: 0.000000 error [op_open] libusb couldn't open USB device /dev/bus/usb/001/002: Permission denied.
I stderr  : libusb: 0.000055 error [op_open] libusb requires write access to USB device nodes.

I have experimented on getting USB permission on runtime and then trying to
access USB device from the native side using this application. But the error
remains. I have conlcuded that the only way to access USB devices on android is
via the java USB API provided by android.

Dependencies
------------
You must have all basic stuff needed for android development. I am listing it
down in case someone needs it.

1. Android SDK
2. Android NDK
3. ant

Besides the above, it is really necessary that adb and ant are on the PATH. This
can be verified by running the following commands in terminal. The output should
be similar to what is shown.

$ adb version
Android Debug Bridge version 1.0.31

$ ant -version
Apache Ant(TM) version 1.9.2 compiled on September 12 2013

How to run
-----------

Change the res/xml/device_filter.xml and jni/open_device.c to include the VID
and PID of the  chipset.
By default it contains VID of FTDI device

To run, make appropriate changes in the build.sh file to give the proper path of
Android SDK and NDK.
Run the following command in the terminal.
a. For x86 devices or emulators
   $ bash build.sh x86
b. For arm devices or emulators
   $ bash build.sh arm

The script will automatically download required data and set it up. It will then
build the android application and install it in the attached android device or
emulator. It will then begin the application and show you the logs.

Procedure
---------
Once the application starts running, the background will turn to red. This means
some error had occurred. It hasn't found a USB device.

Now, connect the USB device to your android. It will now ask for permission to
use with this application. On giving the permission, the activity will refresh
and the background will change to red or green according to the opening of USB
device succeeds or fails.
( It will change to RED every time as it is possible to open usb device only
  through java based android USB API. )