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# Hexagon API app

This is a meta-app that build the necessary binaries for use with
the `HexagonLauncher` utility from `tvm.contrib.hexagon`.

It will build the TVM runtime for Android, the RPC server application
for Android, and the RPC library for Hexagon with the TVM runtime for
Hexagon built into it.

## Configuration

There is a set of configuration variables that are required for cmake:
- `ANDROID_ABI`: Set this to `arm64-v8a`.
- `ANDROID_PLATFORM`: This can be `android-28`.
- `USE_ANDROID_TOOLCHAIN`: The path to the Android toolchain file, i.e.
`android.toolchain.cmake`. This file is a part of the Android NDK.
- `USE_HEXAGON_ARCH`: The version string of the Hexagon architecture
to use, i.e. vNN. The typical setting would be `v68` or later.
- `USE_HEXAGON_SDK`: The path to the Hexagon SDK. Set this path in such
a way that `${USE_HEXAGON_SDK}/setup_sdk_env.source` exists.
- `USE_HEXAGON_TOOLCHAIN`: Path to Hexagon toolchain. It can be the
Hexagon toolchain included in the SDK, for example
`${USE_HEXAGON_TOOLCHAIN}/tools/HEXAGON_Tools/x.y.z/Tools`.  The `x.y.z`
in the path is the toolchain version number, which is specific to the
version of the SDK.

Additionally, the variable `USE_OUTPUT_BINARY_DIR` can be set to indicate
the location where the generated binaries will be placed. If not set, it
defaults to `hexagon_rpc` subdirectory in the current build directory.


## Build

The build will generate the following binaries:
- `tvm_runtime.so`: TVM runtime for Android (shared library).
- `tvm_rpc_android`: RPC server for Android.
- `libhexagon_rpc_skel.so`: RPC library for Hexagon.
- `libtvm_runtime.a`: TVM runtime for Hexagon (static library).

The RPC library for Hexagon contains the TVM runtime, so the static
TVM runtime for Hexagon is not strictly necessary.