This document will guide you to use NPU via Java Native Interface (JNI).

Currently, the source code of NPU JNI is not integrated into the firmware and needs to be downloaded from GitLab.

GitLab repository for Android NPU JNI

GitLab repository for Android NPU demo

1. Download NDK

$ wget https://dl.google.com/android/repository/android-ndk-r17-linux-x86_64.zip

2. Unzip

$ unzip android-ndk-r17-linux-x86_64.zip

3. Configure NDK environment variables:

Open .bashrc and add the following two lines to the end of the file, or add it to the /etc/profile file

$ export NDKROOT=/usr/ndk/android-ndk-r17
$ export PATH=$NDKROOT:$PATH
$ source ~/.bashrc.

4. Check whether the NDK installation is completed: enter the ndk-build command in the shell to check if your installation is successful, if not ndk-build not found is displayed.

After downloading the source code of NPU JNI, enter khadas_android_npu_library/ directory, as follows

$ ll
total 24
drwxr-xr-x 5 root root 4096 Jun  3 13:46 ./
drwxr-xr-x 4 root root 4096 Jun  3 13:45 ../
drwxr-xr-x 5 root root 4096 Jun  4 13:54 detect_code/
drwxr-xr-x 8 root root 4096 Jun  3 14:04 .git/
drwxr-xr-x 5 root root 4096 Jun  3 13:46 model_code/
-rw-r--r-- 1 root root   28 Jun  3 13:45 README.md

1. build libkhadas_npu_jni.so

$ ndk-build 
Android NDK: android-9 is unsupported. Using minimum supported version android-14.    
Android NDK: WARNING: APP_STL gnustl_static is deprecated and will be removed in the next release. Please switch to either c++_static or c++_shared. See https://developer.android.com/ndk/guides/cpp-support.html for more information.    
/bin/sh: 1: test: -ge: unexpected operator
Android NDK: WARNING:jni/Android.mk:khadas_npu_jni: non-system libraries in linker flags: -lopencv_java4    
Android NDK:     This is likely to result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES    
Android NDK:     or LOCAL_SHARED_LIBRARIES instead to list the library dependencies of the    
Android NDK:     current module    
[armeabi-v7a] Install        : libkhadas_npu_jni.so => libs/armeabi-v7a/libkhadas_npu_jni.so

2. build libnn_yoloface.so

$ ndk-build 
Android NDK: android-9 is unsupported. Using minimum supported version android-14.    
Android NDK: WARNING: APP_STL gnustl_static is deprecated and will be removed in the next release. Please switch to either c++_static or c++_shared. See https://developer.android.com/ndk/guides/cpp-support.html for more information.    
/bin/sh: 1: test: -ge: unexpected operator
Android NDK: WARNING:jni/Android.mk:nn_yoloface: non-system libraries in linker flags: -lovxlib    
Android NDK:     This is likely to result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES    
Android NDK:     or LOCAL_SHARED_LIBRARIES instead to list the library dependencies of the    
Android NDK:     current module    
[armeabi-v7a] Install        : libnn_yoloface.so => libs/armeabi-v7a/libnn_yoloface.so

3. build libnn_yolo_v2.so

$ ndk-build 
Android NDK: android-9 is unsupported. Using minimum supported version android-14.    
Android NDK: WARNING: APP_STL gnustl_static is deprecated and will be removed in the next release. Please switch to either c++_static or c++_shared. See https://developer.android.com/ndk/guides/cpp-support.html for more information.    
/bin/sh: 1: test: -ge: unexpected operator
Android NDK: WARNING:jni/Android.mk:nn_yolo_v2: non-system libraries in linker flags: -lovxlib    
Android NDK:     This is likely to result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES    
Android NDK:     or LOCAL_SHARED_LIBRARIES instead to list the library dependencies of the    
Android NDK:     current module    
[armeabi-v7a] Install        : libnn_yolo_v2.so => libs/armeabi-v7a/libnn_yolo_v2.so

4) build libnn_yolo_v3.so

$ ndk-build 
Android NDK: android-9 is unsupported. Using minimum supported version android-14.    
Android NDK: WARNING: APP_STL gnustl_static is deprecated and will be removed in the next release. Please switch to either c++_static or c++_shared. See https://developer.android.com/ndk/guides/cpp-support.html for more information.    
/bin/sh: 1: test: -ge: unexpected operator
Android NDK: WARNING:jni/Android.mk:nn_yolo_v3: non-system libraries in linker flags: -lovxlib    
Android NDK:     This is likely to result in incorrect builds. Try using LOCAL_STATIC_LIBRARIES    
Android NDK:     or LOCAL_SHARED_LIBRARIES instead to list the library dependencies of the    
Android NDK:     current module    
[armeabi-v7a] Install        : libnn_yolo_v3.so => libs/armeabi-v7a/libnn_yolo_v3.so

libkhadas_npu_jni.so: The NPU related API encapsulated by Khadas is called by Khadas NPU demo APP, please refer to khadas_android_npu_library and khadas_android_npu_app code.

libnn_yoloface.so: compiled by YOLOFACE face detection case code which automatically generated by the model conversion tool, For details on how to transfer out the case code, please refer to the description of NPU model conversion in Linux doc.

libnn_yolo_v2.so: compiled by YOLO_v2 image recognition case code which automatically generated by the model conversion tool, For details on how to transfer out the case code, please refer to the description of NPU model conversion in Linux doc.

libnn_yolo_v3.so: compiled by YOLO_v3 image recognition case code which automatically generated by the model conversion tool, For details on how to transfer out the case code, please refer to the descr iption of NPU model conversion in Linux doc.

After download NPU APP source code, app/libs/armeabi-v7a directory include libkhadas_npu_jni.so, libnn_yoloface.so, libnn_yolo_v2.so, libnn_yolo_v3.so and other NPU related library, libovxlib.so etc., The app calls libkhadas_npu_jni.so API by JNI.

$ ll
total 33008
drwxr-xr-x  2 root root     4096 Jun  3 11:31 ./
drwxr-xr-x 20 root root     4096 Jun  3 11:31 ../
-rwxr-xr-x  1 root root     5408 Jun  3 11:31 ld-android.so*
-rw-r--r--  1 root root   227220 Jun  3 11:31 libarchmodelSw.so
-rwxr-xr-x  1 root root   657000 Jun  3 11:31 libc++_shared.so*
-rwxr-xr-x  1 root root   832796 Jun  3 11:31 libc.so*
-rw-r--r--  1 root root   636316 Jun  3 11:31 libc++.so
-rw-r--r--  1 root root    67444 Jun  3 11:31 libcutils.so
-rwxr-xr-x  1 root root     5940 Jun  3 11:31 libdl.so*
-rw-r--r--  1 root root  1273224 Jun  3 11:31 libGAL.so
-rwxr-xr-x  1 root root    26312 Jun  3 11:31 libkhadas_npu_jni.so*
-rwxr-xr-x  1 root root    89020 Jun  3 11:31 liblog.so*
-rwxr-xr-x  1 root root   136680 Jun  3 11:31 libm.so*
-rw-r--r--  1 root root   226016 Jun  3 11:31 libNNArchPerf.so
-rwxr-xr-x  1 root root    18032 Jun  3 11:31 libnn_yoloface.so*
-rwxr-xr-x  1 root root    22180 Jun  3 11:31 libnn_yolo_v2.so*
-rwxr-xr-x  1 root root    22252 Jun  3 11:31 libnn_yolo_v3.so*
-rw-r--r--  1 root root 10076740 Jun  3 11:31 libopencv_java4.so
-rw-r--r--  1 root root  1669588 Jun  3 11:31 libOpenVX.so
-rw-r--r--  1 root root  2763276 Jun  3 11:31 libovxlib.so
-rwxr-xr-x  1 root root    15928 Jun  3 11:31 libsync.so*
-rw-r--r--  1 root root 14976940 Jun  3 11:31 libVSC.so