Can it run Doom? Part 1: a C library with no operating system
Doom expects a C library and a filesystem. A bare-metal Pi has neither, so the C library's bottom layer is written in Rust.
Blog
Can it run Doom? Part 2: the framebuffer
Getting Doom's frames onto the screen, and letting the GPU scale them to fill any display without distorting them.
Can it run Doom? Part 3: a USB keyboard
A Pi has no keyboard port, only USB. Reading a keyboard means being a USB host, and then speaking Doom's 1993 idea of a key.
Can it run Doom? Part 4: sound and music on their own core
Sound effects, and the original OPL music on an emulated Yamaha FM chip, mixed on a second core and played out of the 3.5 mm jack.
Introducing rpi-hal
Bare-metal Rust on the Raspberry Pi, with no operating system underneath.