Moving Raspberry Pi GPIO code to libgpiod: why do pin numbers need another check?

Map the physical header pin to the intended signal using documentation for the exact Pi model. Then inspect the running kernel's GPIO chips and line information. Do not assume a hardcoded chip number and offset remain identical across board models or kernel configurations.

Use the relevant libgpiod version's API and examples, because command syntax and bindings can differ between major versions. Request the intended direction, active polarity and edge behavior explicitly. Check whether another driver already owns the line before attempting to control it.

For standard devices such as buttons, LEDs or buses, consider the existing kernel subsystem driver rather than recreating its behavior in userspace. Test initial and release states as well as the active loop. GPIO access through Linux is not a guarantee of deterministic microsecond timing.