STM32 BootLoader, document by http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/CD00167594.pdf
The instructions are detailed more fully here: http://leaflabs.com/docs/bootloader.html#flashing-a-custom-bootloader
Board: MiCOKit-3288 by: http://mico.io CPU: stm32f411
Base on mbed(CMSIS) 20150707
Complier: gcc-arm-none-eabi-4_9-2015q2, information from espruino Debug SWD: stlink-v2
CMD:
#make
#make flash
#cutecom
serial: 115200,8N1 LED is GPIOB-12 default USART: usart2
tools/stm32loader.py
good luck.