We have all probably turned on an LED with the classical 5V + 330 (or so) Ohm resistor combination. Failing to limit the current would result in a burnt LED. Besides resistors, one may also use LED drivers to control their brightness and limit the current going through them. The LED1642GW by ST is one of such LED drivers. It sinks current, has 16 channels and can be controlled by an external MCU through a serial link....
Implementing your own bare metal USB stack may provide certain benefits like little to no dependencies, smaller code size, better understanding of internals and suffering. This article documents the process I went through to manually set up and get the USB core of an STM32F401CCU6 to do what I wanted. My goal was to successfully return a device descriptor. Once I got that working I had a greater appreciation for TinyUSB and went with it, however this was still a painful great learning experience....