libopencm3 based Makefile for c programming on the stm32 black pill,. STM32F411CEU6
Makefile came from the very good book "Begining STM32 Programming" and was slightly tweaked for the black pill. The source for that book, where the makefile and dir layout was taken is here: https://github.com/ve3wwg/stm32f103c8t6