A freestanding C implementation doesn't have to include anything but a handful of headers with some macro and type definitions. It's not uncommon to get a manuf

A freestanding C implementation doesn't have to include anything but a handful of headers with some macro and type definitions. It's not uncommon to get a manufacturer-specific library whose features are specific to the particular controller architecture, not related to those defined in the full C library. And it's not uncommon for embedded software developers to ignore those libraries, which are frequently terrible, and write everything from scratch.