Inference Runner Code Sample


This document describes the process of setting up and running the Arm® Ethos™-U NPU Inference Runner.

The inference runner is intended for quickly checking profiling results for any wanted network, providing it has been processed by the Vela compiler.

A simple model is provided with the Inference Runner as an example. However, we expect you to replace this model with one that you must profile.

For further details, refer to: Add custom model.

The inference runner populates all input tensors for the provided model with randomly generated data and an inference is then performed. Profiling results are then displayed in the console.

The example use-case code can be found in the following directory: source/use_case/inference_runner.


See Prerequisites

Building the Code Samples application from sources

Build options

In addition to the already specified build option in the main documentation, the Inference Runner use-case adds the following:

  • inference_runner_MODEL_TFLITE_PATH - The path to the NN model file in the TFLite format. The model is then processed and included in the application axf file. The default value points to one of the delivered set of models.

    Note that the parameters TARGET_PLATFORM and ETHOS_U_NPU_ENABLED must be aligned with the chosen model. In other words:

    • If ETHOS_U_NPU_ENABLED is set to On or 1, then the NN model is assumed to be optimized. The model naturally falls back to the Arm® Cortex®-M CPU if an unoptimized model is supplied.
    • if ETHOS_U_NPU_ENABLED is set to Off or 0, the NN model is assumed to be unoptimized. Supplying an optimized model in this case results in a runtime error.
  • inference_runner_ACTIVATION_BUF_SZ: The intermediate, or activation, buffer size reserved for the NN model. By default, it is set to 2MiB and is enough for most models.

  • inference_runner_DYNAMIC_MEM_LOAD_ENABLED: This can be set to ON or OFF, to allow dynamic model load capability for use with MPS3 FVPs. See section Building with dynamic model load capability below for more details.

To build ONLY the Inference Runner example application, add -DUSE_CASE_BUILD=inference_runner to the cmake command line, as specified in: Building.

Build process

Note: This section describes the process for configuring the build for the MPS3: SSE-300. To build for a different target platform, please refer to: Building.

Create a build directory and navigate inside, like so:

mkdir build_inference_runner && cd build_inference_runner

On Linux, when providing only the mandatory arguments for the CMake configuration, execute the following command to build only Image Classification application to run on the Ethos-U55 Fast Model:

cmake ../ -DUSE_CASE_BUILD=inference_runner

To configure a build that can be debugged using Arm DS specify the build type as Debug and then use the Arm Compiler toolchain file:

cmake .. \
    -DCMAKE_TOOLCHAIN_FILE=scripts/cmake/toolchains/bare-metal-armclang.cmake \

For further information, please refer to:

Note: If re-building with changed parameters values, we recommend that you clean the build directory and re-run the CMake command.

If the CMake command succeeds, build the application as follows:

make -j4

To see compilation and link details, add VERBOSE=1.

Results of the build are placed under the build/bin folder, like so:

 ├── ethos-u-inference_runner.axf
 ├── ethos-u-inference_runner.htm
 └── sectors
      └── inference_runner
        ├── ddr.bin
        └── itcm.bin

The bin folder contains the following files:

  • ethos-u-inference_runner.axf: The built application binary for the Inference Runner use-case.

  • Information from building the application. For example: The libraries used, what was optimized, and the location of objects.

  • ethos-u-inference_runner.htm: Human readable file containing the call graph of application functions.

  • sectors/inference_runner: Folder containing the built application. It is split into files for loading into different FPGA memory regions.

  • sectors/images.txt: Tells the FPGA which memory regions to use for loading the binaries in the sectors/.. folder.

Add custom model

The application performs inference using the model pointed to by the CMake parameter inference_runner_MODEL_TFLITE_PATH.

Note: If you want to run the model using an Ethos-U, ensure that your custom model has been successfully run through the Vela compiler before continuing.

For further information: Optimize model with Vela compiler.

Then, you must set inference_runner_MODEL_TFLITE_PATH to the location of the Vela processed model file.

An example:

cmake .. \
  -Dinference_runner_MODEL_TFLITE_PATH=<path/to/custom_model_after_vela.tflite> \

Note: Clean the build directory before re-running the CMake command.

The .tflite model file pointed to by inference_runner_MODEL_TFLITE_PATH is converted to C++ files during the CMake configuration stage. It is then compiled into the application for performing inference with.

The log from the configuration stage tells you what model path and labels file have been used, for example:

-- User option inference_runner_MODEL_TFLITE_PATH is set to <path/to/custom_model_after_vela.tflite>
-- Using <path/to/custom_model_after_vela.tflite>
++ Converting custom_model_after_vela.tflite to\

After compiling, your custom model has now replaced the default one in the application.

Setting up and running Ethos-U NPU code sample

Setting up the Ethos-U NPU Fast Model

The FVP is available publicly from Arm Ecosystem FVP downloads.

For the Ethos-U evaluation, please download the MPS3 based version of the Arm® Corstone™-300 model that contains Cortex-M55 and offers a choice of the Ethos-U55 and Ethos-U65 processors.

To install the FVP:

  • Unpack the archive.

  • Run the install script in the extracted package:

  • Follow the instructions to install the FVP to the required location.

Starting Fast Model simulation

Once completed the building step, the application binary ethos-u-inference_runner.axf can be found in the build/bin folder.

Assuming that the install location of the FVP was set to ~/FVP_install_location, then the simulation can be started by using:

~/FVP_install_location/models/Linux64_GCC-6.4/FVP_Corstone_SSE-300_Ethos-U55 -a ./bin/mps3-sse-300/ethos-u-inference_runner.axf

A log output appears on the terminal:

telnetterminal0: Listening for serial connection on port 5000
telnetterminal1: Listening for serial connection on port 5001
telnetterminal2: Listening for serial connection on port 5002
telnetterminal5: Listening for serial connection on port 5003

This also launches a telnet window with the standard output of the sample application. It also includes error log entries containing information about the pre-built application version, TensorFlow Lite Micro library version used, and data types. The log also includes the input and output tensor sizes of the model compiled into the executable binary.

Running Inference Runner

After the application has started the inference starts immediately and it outputs the results on the telnet terminal.

The following example illustrates application output:

INFO - Final results:
INFO - Profile for Inference :
INFO - NPU ACTIVE cycles: 33145
INFO - NPU IDLE cycles: 1033
INFO - NPU TOTAL cycles: 34178

After running an inference on randomly generated data, the output of the log shows the profiling results that for this inference. For example:

  • Ethos-U PMU report:

    • 34,178 total cycle: The number of NPU cycles.

    • 33,145 active cycles: The number of NPU cycles that were used for computation.

    • 1,033 idle cycles: The number of cycles for which the NPU was idle.

    • 9,332 AXI0 read beats: The number of AXI beats with read transactions from AXI0 bus. AXI0 is the bus where the Ethos-U NPU reads and writes to the computation buffers, activation buf, or tensor arenas.

    • 3,248 AXI0 write beats: The number of AXI beats with write transactions to AXI0 bus.

    • 2,219 AXI1 read beats: The number of AXI beats with read transactions from AXI1 bus. AXI1 is the bus where the Ethos-U NPU reads the model. So, read-only.

  • For FPGA platforms, a CPU cycle count can also be enabled. However, do not use cycle counters for FVP, as the CPU model is not cycle-approximate or cycle-accurate.

Building with dynamic model load capability

It is possible to build the inference runner application, targeting only the FVP environment, that allows loading of the TFLite model file at runtime. In this build configuration, the model TFLite file is not baked into the application but the application expects this model binary to be loaded at a specific address by an external agent. This loading capability also extends to the input data for the model.

This feature depends on these addresses to be specified in target platform's CMake description and, by default, is available for use on the MPS3 FVP platform.

Note:: The application built with this support will not work on the FPGA. This capability is only provided for use with the FVP, to make it easier to try different ML workloads without having to build the applications with different TFLite files baked into the application statically. Also, this feature is not available for native target.

The parameter inference_runner_DYNAMIC_MEM_LOAD_ENABLED should be set to ON in the CMake configuration command to enable this feature. For example, from a freshly created build directory, run:

cmake .. \
  -Dinference_runner_DYNAMIC_MEM_LOAD_ENABLED=ON \

Once the configuration completes, running:

make -j

will build the application that will expect the neural network model and the IFM to be loaded into specific addresses. The default values for these addresses are defined in the use-case CMake file.

Running the FVP with dynamic model loading

If the application has been built with dynamic loading capability, as described in the previous section, the FVP can be invoked with command line parameters that will load specific data into memory. For example, the command below loads a custom model at address 0x90000000, a custom input from address 0x92000000 and when the FVP exits, it dumps a file named output.bin with the output tensors consolidated into a binary blob.

Note: The CMake profile for the target should also give an indication of the maximum sizes for each of the regions. This is also mentioned in the linker scripts for the same target. For MPS3, the model size can be a maximum of 32MiB. The IFM and OFM spaces are both reserved as 16MiB sections.

~/FVP_install_location/models/Linux64_GCC-6.4/FVP_Corstone_SSE-300_Ethos-U55 \
  -a ./bin/ethos-u-inference_runner.axf \
  --data /path/to/custom-model.tflite@0x90000000 \
  --data /path/to/custom-ifm.bin@0x92000000 \
  --dump cpu0=/path/to/output.bin@Memory:0x93000000,1024

The above command will dump a 1KiB (1024 bytes) file with output tensors as a binary blob after it has consumed the model and IFM data provided by the file paths specified and the inference is executed successfully. If the size of the output tensors is unknown before running the FVP, it can be run without the --dump parameter to check the size of the output first by looking at the application log. Alternatively, a size of 16MiB will dump the whole reserved section for the OFM to a file.

Note:: When there are multiple input tensors, the application is set up to iterate over all of them and populate each of them, in sequence, with the required amount of data. The sequence in which these tensors are populated is governed by the index assigned to them within the TensorFlow Lite Micro framework. So, the input binary blob should be a consolidated file containing data for all the input tensors. The same packing is used for output binary dumps.