How to use OpenBLAS on Cortex M

Cortex-M is a widely used microcontroller that is present in a variety of industrial and consumer electronics. A common variant of the Cortex-M is the STM32F4xx series. Here, we will give instructions for building for the STM32F4xx.

First, install the embedded arm gcc compiler from the arm website. Then, create the following toolchain file and build as follows.

# cmake .. -G Ninja -DCMAKE_C_COMPILER=arm-none-eabi-gcc -DCMAKE_TOOLCHAIN_FILE:PATH="toolchain.cmake" -DNOFORTRAN=1 -DTARGET=ARMV5

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR arm)

set(CMAKE_C_COMPILER "arm-none-eabi-gcc.exe")
set(CMAKE_CXX_COMPILER "arm-none-eabi-g++.exe")

set(CMAKE_EXE_LINKER_FLAGS "--specs=nosys.specs" CACHE INTERNAL "")

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

In your embedded application, the following functions need to be provided for OpenBLAS to work correctly:

void free() {}
void malloc() {}
void puts() {}
void printf() {}
void getenv() {}
void atoi() {}

Note: if you are developing for an embedded platform, it is your responsibility to make sure that the device has sufficient memory for malloc calls.