Raspberry Pi OS - Baking Pi Tutorial (Lessons 1-6)

A bare-metal operating system for Raspberry Pi built from scratch using ARM assembly language.

Project Overview

This project implements a minimal operating system following Cambridge University's "Baking Pi" tutorial series. It demonstrates low-level hardware programming without any existing OS layer.

Features Implemented

• Lesson 1-2 (OK01-OK02): GPIO control and LED blinking
• Lesson 3 (OK03): Functions, stack management, and code organization
• Lesson 4 (OK04): System timer for precise delays
• Lesson 5 (OK05): Data storage and pattern sequences
• Lesson 6 (Screen01): Framebuffer graphics and screen output

File Structure

baking-pi/
├── source/
│   ├── main.s              # Main program entry and rendering loop
│   ├── gpio.s              # GPIO controller functions
│   ├── systemTimer.s       # System timer functions
│   ├── mailbox.s           # Mailbox communication with GPU
│   └── framebuffer.s       # Framebuffer initialization
├── build/                  # Compiled object files (generated)
├── Makefile                # Build automation
├── kernel.ld               # Linker script
└── kernel.img              # Final kernel image (generated)

Prerequisites

WSL/Linux

sudo apt-get update
sudo apt-get install gcc-arm-none-eabi make qemu-system-arm

Building

# Clean build
make clean

# Compile
make

This generates kernel.img which can be run on Raspberry Pi or in QEMU.

Testing in QEMU

qemu-system-arm -m 1024 -M raspi2b -kernel kernel.img -serial stdio

You should see a colorful gradient pattern on the screen!

How It Works

1. Boot: The Raspberry Pi loads kernel.img at address 0x8000
2. Initialization: Sets up stack pointer and initializes framebuffer
3. GPU Communication: Uses mailbox to request framebuffer from GPU
4. Rendering: Continuously draws pixels to screen memory
5. Display: GPU reads framebuffer and outputs to screen

Technical Details

• Architecture: ARMv6 (Raspberry Pi 1)
• Assembler: GNU ARM Assembler (arm-none-eabi-as)
• Display Mode: High Color (16-bit, 65,536 colors)
• Resolution: 1024x768 pixels
• Memory Layout: Code at 0x8000, stack grows down from 0x8000

Key Concepts Learned

• ARM assembly language and instruction set
• Bare-metal hardware programming
• Memory-mapped I/O
• Function calling conventions (ABI)
• Stack management
• Hardware timers
• DMA and GPU communication
• Framebuffer graphics

Next Steps

Continue with:

• Screen02-04: Drawing lines, text, and terminal output
• Input01-02: Keyboard and mouse input

Resources

• Baking Pi Tutorial
• ARM Architecture Reference Manual
• BCM2835 Peripherals Guide

License

Educational project following Cambridge University's Baking Pi tutorial.