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MNN Hexagon Backend

source/backend/hexagon/README.md

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MNN Hexagon Backend

This directory contains the Hexagon backend implementation for MNN. It supports accelerating model inference on Qualcomm Hexagon DSPs.

Prerequisites

  • Hexagon SDK: Ensure you have downloaded and installed the Qualcomm Hexagon SDK.
  • Environment Variable: Set the HEXAGON_SDK_ROOT environment variable pointing to the root of your Hexagon SDK installation.

Compilation Steps

1. Compile the Custom HTP Ops Library

Before compiling MNN, you need to build the custom Hexagon Tensor Processor (HTP) operator library located in htp-ops-lib/.

bash
cd source/backend/hexagon/htp-ops-lib

# Pass the target DSP architecture version (e.g., v73, v75, v79)
# Ensure your Hexagon SDK environment is properly set up before running this script
bash build.sh v79

This script will generate two essential libraries in the htp-ops-lib/outputs/ directory:

  • libMNN_htpops.so: The Android AArch64 stub library that runs on the CPU.
  • libMNN_htpops_skel.so: The Hexagon DSP skeleton library that runs on the Hexagon NPU/DSP.

2. Compile MNN with Hexagon Backend Enabled

When configuring the MNN build, you need to enable the Hexagon backend by passing the -DMNN_HEXAGON=ON flag to CMake. Don't need Hexagon SDK.

bash
cd /path/to/MNN
mkdir build && cd build

cmake .. \
  -DMNN_HEXAGON=ON \
  # ... other MNN compilation flags (e.g., cross-compiling for Android)

make -j8

Note: If you have already exported HEXAGON_SDK_ROOT in your environment, you can omit the -DHEXAGON_SDK_ROOT CMake argument.

3. Deployment and Execution

To run the compiled MNN with the Hexagon backend on an Android device:

  1. Push your compiled MNN executable and libraries to the device.
  2. Push the generated libMNN_htpops.so and libMNN_htpops_skel.so libraries to the device.
  3. Configure your LD_LIBRARY_PATH so the system can find libMNN_htpops.so.
  4. Configure the ADSP_LIBRARY_PATH environment variable to include the directory containing libMNN_htpops_skel.so so the DSP can load the skeleton library.
bash
# Example on device:
export ADSP_LIBRARY_PATH="/data/local/tmp/hexagon_libs;/vendor/lib/rfsa/adsp;/system/lib/rfsa/adsp"
export LD_LIBRARY_PATH="/data/local/tmp/hexagon_libs:$LD_LIBRARY_PATH"