Exteral Reference

These are all great websites you can refer to.

Bare metal tutorials in C

https://github.com/bztsrc/raspi3-tutorial

Operating system tutorials in C

https://github.com/s-matyukevich/raspberry-pi-os

Operating system tutorials in rust

https://github.com/rust-embedded/rust-raspi3-OS-tutorials

Raspberry pi officical github

https://github.com/raspberrypi/

Embedded linux wiki page for Raspberry pi

https://elinux.org/RPi_Hub