SharanSMenon / rpi-02W-custom-kernel

A bare metal kernel for the Raspberry Pi 02 W.

Raspberry Pi Zero 2W Bare Metal Kernel

This is a baremetal kernel for the Raspberry Pi Zero 2W. It can also work on a Raspberry Pi 3, since they both use the same chipset. I have not tested it on a Raspberry Pi 3, however.

Features implemented

• Write to screen
• Draw on screen
• Write to serial console via UART
• Control power state
• Control GPIO
• Generate Random Numbers with hardware RNG
• Mailbox to communicate to VideoCore GPU
• Timer
• sprintf implemented for string operations/debugging

Build instructions

I build this kernel on an Apple Silicon Mac using the Clang compiler installed with homebrew. You can install it via the brew install llvm commmand. This makefile is designed for the clang compiler. If you are using another compiler (e.g arm-gcc), you will need to modify the makefile.

1. Clone this repository
2. Run the make command
3. Follow the setup directions in the microSD card setup section
4. Copy the kernel8.img file to a microSD card

microSD card setup

1. Ensure the microSD card is formatted as FAT32.
2. From this url (https://github.com/raspberrypi/firmware/tree/master/boot), copy start.elf, bootcode.bin, and fixup.dat to the microSD card.

You can also setup the microSD card by just installing Raspbian on the card and then removing all files that starts with kernel, replacing it with the one you built here.

When the Raspberry Pi Zero 2W boots, the GPU starts instead of the CPU. bootcode.bin is proprietary firmware for the GPU that will direct the GPU to boot the ARM CPU using the kernel8.img file. Mailboxes are used for CPU-GPU communication.