If the hardware files provided from the chip manufacturer aren't open source you might consider using libopencm3 (http://libopencm3.org/wiki/Main_Page) too.
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-M0(+)/M3/M4 microcontrollers, including ST STM32, Ti Tiva and Stellaris, NXP LPC 11xx, 13xx, 15xx, 17xx parts, Atmel SAM3, Energy Micro EFM32 and others.
Any plans to make the rest of the source code open source too? E.g. the part it talks to the hardware.
Like Trezor has it: https://github.com/trezor/trezor-mcu
If the hardware files provided from the chip manufacturer aren't open source you might consider using libopencm3 (http://libopencm3.org/wiki/Main_Page) too.
https://opensource.com/business/15/7/why-open-hardware-winning