Open-Source lowlevel hardware library for ARM Cortex-M3 microcontrollers (but also M0, M4 are supported and more to come)
The libopencm3 project (previously known as libopenstm32) aims to create a free/libre/open-source (LGPL v3, or later) firmware library for various ARM Cortex-M3 microcontrollers, including ST STM32, Toshiba TX03, Atmel SAM3U, NXP LPC1000, EFM32 and others.
Up to date information is available in the GitHub wiki
from the mailing list firstname.lastname@example.org and the IRC channel (libera.chat, #libopencm3).
Daily updated autogenerated API documentation for developers: