Your best bet is https://github.com/espruino/Espruino/blob/master/targets/stm32/jshardware.c#L1589
@Gordon started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Your best bet is https://github.com/espruino/Espruino/blob/master/targets/stm32/jshardware.c#L1589