Export: C++/STM32

N2D2-IP only: available upon request.

Export type: CPP_STM32

C++ export for STM32.

n2d2 MobileNet_ONNX.ini -seed 1 -w /dev/null -export CPP_STM32

Principle

This export inherit the properties and optimizations from the C++ export, but includes optimized kernels for the Cortex-M4 and the Cortex-M7. Please refer to the Export: C++ for the available export parameters.

SIMD

The SMLAD intrinsic is used to do two 16-bit signed integers multiplications with accumulation. To extend the 8-bit data to the necessary 16-bit, the XTB16 intrinsic is used.

Loop unrolling

The unrolling of the loops can be done with #pragma GCC unroll NB_ITERATIONS but it does not always perform as well as expected. Some loops are manually unrolled instead using C++ templates. This increases the size of the compiled binary further but it provides a faster inference.

Usage of intrinsics

Intrinsics provided by ARM are preferred to normal library methods calls when possible. For example the SSAT and USAT intrinsics are used to clamp the output value resulting in better results than a naive call to the std::clamp method.

Usage

n2d2 MobileNet_ONNX.ini -seed 1 -w /dev/null -export CPP_STM32 -fuse -nbbits 8 -calib -1 -db-export 100 -test

This command generates a C++ project in the sub-directory export_CPP_STM32_int8. This project is ready to be cross-compiled with a Makefile, using the GNU Arm Embedded Toolchain (which provides the arm-none-eabi-gcc compiler).

make

To cross-compile the project using the GNU Arm Embedded Toolchain. An ELF binary file is generated in bin/n2d2_stm32.elf.

make flash

To flash the board using OpenOCD with the previously generated bin/n2d2_stm32.elf binary. In the provided Makefile, the default OpenOCD location is /usr/local/bin/openocd and the default script is stm32h7x3i_eval.cfg, for the STM32H7x3I evaluation board family. These can be changed in the first lines of the Makefile.