https://github.com/danieleff/STM32GENERIC
but i have not committed the changes needed for the Borg there yet, so please use:
https://github.com/Spawn32/STM32GENERIC
Unzip it into [Arduino]/hardware folder
Download the latest GNU ARM Embedded Toolchain:
https://developer.arm.com/open-source/gnu-toolchain/gnu-rm/downloads
(The one in Arduino dosen’t support STM32F7).
Change compiler.path in platform.txt to point to that you downloaded.
You will also need the latest Arduino 1.9.0-beta or newer.
This HAL is a modified version of Chris Barr’s Picoprint STM32F4 HAL, so shouldn’t be to hard to get it to work on a F4.