libusb for Android

Building:

To build libusb for Android do the following:

1. Download the latest NDK from: http://developer.android.com/tools/sdk/ndk/index.html

2. Extract the NDK.

3. Open a shell and make sure there exist an NDK global variable set to the directory where you extracted the NDK.

4. Change directory to libusb's "android/jni"

5. Run "$NDK/ndk-build".

The libusb library, examples and tests can then be found in: "android/libs/$ARCH"

Where $ARCH is one of: armeabi armeabi-v7a mips mips64 x86 x86_64

Installing:

If you wish to use libusb from native code in own Android application then you should add the following line to your Android.mk file:

include $(PATH_TO_LIBUSB_SRC)/android/jni/libusb.mk

You will then need to add the following lines to the build configuration for each native binary which uses libusb:

LOCAL_C_INCLUDES += $(LIBUSB_ROOT_ABS) LOCAL_SHARED_LIBRARIES += libusb1.0

The Android build system will then correctly include libusb in the application package (APK) file, provided ndk-build is invoked before the package is built.

Runtime Permissions:

The Runtime Permissions on Android can be transferred from Java to Native over the following approach:

JAVA:

--> Obtain USB permissions over the android.hardware.usb.UsbManager class

  usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
  HashMap<String, UsbDevice> deviceList = usbManager.getDeviceList();
  for (UsbDevice usbDevice : deviceList.values()) {
      usbManager.requestPermission(usbDevice, mPermissionIntent);
  }

--> Get the native FileDescriptor of the UsbDevice and transfer it to Native over JNI or JNA

  UsbDeviceConnection usbDeviceConnection = usbManager.openDevice(camDevice);
  int fileDescriptor = usbDeviceConnection.getFileDescriptor();

--> JNA sample method:

  JNA.INSTANCE.set_the_native_Descriptor(fileDescriptor);

NATIVE:

--> Initialize libusb on Android

  set_the_native_Descriptor(int fileDescriptor) {
      libusb_context *ctx;
      libusb_device_handle *devh;
      libusb_set_option(&ctx, LIBUSB_OPTION_NO_DEVICE_DISCOVERY, NULL);
      libusb_init(&ctx);
      libusb_wrap_sys_device(NULL, (intptr_t)fileDescriptor, &devh);
  }
  /* From this point you can regularly use all libusb functions as usual */

About LIBUSB_OPTION_NO_DEVICE_DISCOVERY:

The method libusb_set_option(&ctx, LIBUSB_OPTION_NO_DEVICE_DISCOVERY, NULL)
does not affect the ctx.
It allows initializing libusb on unrooted Android devices by skipping
the device enumeration.

Rooted Devices:

For rooted devices the code using libusb could be executed as root
using the "su" command. An alternative would be to use the "su" command
to change the permissions on the appropriate /dev/bus/usb/ files.

Users have reported success in using android.hardware.usb.UsbManager
to request permission to use the UsbDevice and then opening the
device. The difficulties in this method is that there is no guarantee
that it will continue to work in the future Android versions, it
requires invoking Java APIs and running code to match each
android.hardware.usb.UsbDevice to a libusb_device.

For a rooted device it is possible to install libusb into the system
image of a running device:

 1. Enable ADB on the device.

 2. Connect the device to a machine running ADB.

 3. Execute the following commands on the machine
    running ADB:

    # Make the system partition writable
    adb shell su -c "mount -o remount,rw /system"

    # Install libusb
    adb push obj/local/armeabi/libusb1.0.so /sdcard/
    adb shell su -c "cat > /system/lib/libusb1.0.so < /sdcard/libusb1.0.so"
    adb shell rm /sdcard/libusb1.0.so

    # Install the samples and tests
    for B in listdevs fxload xusb sam3u_benchmark hotplugtest stress
    do
      adb push "obj/local/armeabi/$B" /sdcard/
      adb shell su -c "cat > /system/bin/$B < /sdcard/$B"
      adb shell su -c "chmod 0755 /system/bin/$B"
      adb shell rm "/sdcard/$B"
    done

    # Make the system partition read only again
    adb shell su -c "mount -o remount,ro /system"

    # Run listdevs to
    adb shell su -c "listdevs"

 4. If your device only has a single OTG port then ADB can generally
    be switched to using Wifi with the following commands when connected
    via USB:

    adb shell netcfg
    # Note the wifi IP address of the phone
    adb tcpip 5555
    # Use the IP address from netcfg
    adb connect 192.168.1.123:5555