Optimise TensorFlow Lite models for Ethos-U55 NPU.

Vela

This tool is used to compile a TensorFlow Lite for Microcontrollers neural network model into an optimised version that can run on an embedded system containing an Ethos-U55 NPU.

The optimised model will contain TensorFlow Lite Custom operators for those parts of the model that can be accelerated by the Ethos-U55. Parts of the model that cannot be accelerated are left unchanged and will instead run on the Cortex-M series CPU using an appropriate kernel (such as the Arm optimised CMSIS-NN kernels).

After compilation the optimised model can only be run on an Ethos-U55 NPU embedded system.

The tool will also generate performance estimates (EXPERIMENTAL) for the compiled model.

TensorFlow Support

Vela supports TensorFlow 2.1.0.

Environment

Vela runs on the Linux operating system.

Prerequisites

The following should be installed prior to the installation of Vela:

• Python >= 3.6
• Pip3
• GNU toolchain (GCC, Binutils and libraries) or alternative C compiler/linker toolchain

And optionally:

• Pipenv virtual environment tool

Installation

Before running, the Vela package must be installed along with all its dependencies. To do this, first change to the directory that contains this README.md file. Then use the command:

pip3 install -U setuptools>=40.1.0
pip3 install .


Or, if you use pipenv:

pipenv install .


Running

Vela is run with an input .tflite file passed on the command line. This file contains the neural network to be compiled. The tool then outputs an optimised version with a _vela.tflite file prefix, along with the performance estimate (EXPERIMENTAL) CSV files, all to the output directory.

If you use the pipenv virtual environment tool then first start by spawning a shell in the virtual environment.:

pipenv shell


After which running Vela is the same regardless of whether you are in a virtual environment or not.

Example usage:

1. Compile the network my_model.tflite. The optimised version will be output to ./output/my_network_vela.tflite.
vela my_model.tflite

1. Compile the network /path/to/my_model.tflite and specify the output to go in the directory ./results_dir/.
vela --output-dir ./results_dir /path/to/my_model.tflite

1. To specify information about the embedded system's configuration use Vela's system configuration file. The following command selects the MySysConfig settings that are described in the sys_cfg_vela.ini system configuration file. More details can be found in the next section.
vela --config sys_cfg_vela.ini --system-config MySysConfig my_model.tflite

1. To get a list of all available options:
vela --help


Information about all of Vela's CLI options as well as the system configuration file format can be found in Vela Options

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