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Halide for Hexagon HVX

Halide supports offloading work to Qualcomm Hexagon DSP on Qualcomm Snapdragon 845/710 devices or newer. The Hexagon DSP provides a set of 128 byte vector instruction extensions - the Hexagon Vector eXtensions (HVX). HVX is well suited for image processing, and Halide for Hexagon HVX will generate the appropriate HVX vector instructions from a program authored in Halide.

Halide can be used to compile Hexagon object files directly, by using a target such as hexagon-32-qurt-hvx.

Halide can also be used to offload parts of a pipeline to Hexagon using the hexagon scheduling directive. To enable the hexagon scheduling directive, include the hvx target feature in your target. The currently supported combination of targets is to use the HVX target features with an x86 linux host (to use the simulator) or with an ARM android target (to use Hexagon DSP hardware). For examples of using the hexagon scheduling directive on both the simulator and a Hexagon DSP, see the blur example app.

To build and run an example app using the Hexagon target,

1. Obtain and build trunk LLVM and Clang. (Earlier versions of LLVM may work but are not actively tested and thus not recommended.)
2. Download and install the Hexagon SDK and Hexagon Tools. Hexagon SDK 4.3.0 or later is needed. Hexagon Tools 8.4 or later is needed.
3. Build and run an example for Hexagon HVX

# 1. Obtain and build trunk LLVM and Clang

(Follow the instructions given previously, just be sure to check out the main branch.)

# 2. Download and install the Hexagon SDK and Hexagon Tools

Go to https://qpm.qualcomm.com/#/main/home

1. Go to Tools, and download Qualcomm Package Manager 3. Install the package manager on your machine.
2. Run the installed Qualcomm Package Manager and install the Qualcomm Hexagon SDK 5.x (or 4.x). The SDK can be selected from the Qualcomm Hexagon SDK Products.
3. Set an environment variable to point to the SDK installation location
   export SDK_LOC=/location/of/SDK

# 3. Build and run an example for Hexagon HVX

In addition to running Hexagon code on device, Halide also supports running Hexagon code on the simulator from the Hexagon tools.

To build and run the blur example in Halide/apps/blur on the simulator:

cd apps/blur
export HL_HEXAGON_SIM_REMOTE=../../src/runtime/hexagon_remote/bin/v65/hexagon_sim_remote
export HL_HEXAGON_TOOLS=$SDK_LOC/Hexagon_Tools/8.x/Tools/
LD_LIBRARY_PATH=../../src/runtime/hexagon_remote/bin/host/:$HL_HEXAGON_TOOLS/lib/iss/:. HL_TARGET=host-hvx make test

# To build and run the blur example in Halide/apps/blur on Android:

To build the example for Android, first ensure that you have Android NDK r19b or later installed, and the ANDROID_NDK_ROOT environment variable points to it. (Note that Qualcomm Hexagon SDK v4.3.0 includes Android NDK r19c, which is fine.)

Now build and run the blur example using the script to run it on device:

export HL_HEXAGON_TOOLS=$SDK_LOC/HEXAGON_Tools/8.4.11/Tools/
HL_TARGET=arm-64-android-hvx ./adb_run_on_device.sh