Coyt Barringer wrote a post on his blog showing how he program the Blue Pill STM32F103 using USB Bootloader and PlatformIO:
This is the infamous Blue Pill board – a $2 ARM STM32F103 development board with all the capabilities of a Teensy 3.x at a fraction of the price of an Arduino. So what’s the catch?
I’ll tell you – software support.
A couple weeks ago I decided to invest some time learning this platform because I was sick of paying 20+ dollars for a Teensy. While the PJRC platforms are fantastic, they are expensive and need a proprietary boot loader in order to work. I want a small and powerful arm chip which I can integrate INTO my own PCBs and the Teensy does not easily or cheaply allow this. The Blue Pill and it’s derivatives appear to be just the thing I need!
See the full post at lostengineer.com.