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Building a Raspberry Pi OS from Scratch

Welcome to the OS Development series! In this comprehensive tutorial, we'll build a bare-metal operating system for the Raspberry Pi 4B from the ground up.

⚠️ Disclaimer

Proceed at your own risk. This tutorial involves low-level hardware programming. While every effort has been made to ensure the correctness of the code, writing directly to hardware registers carries inherent risks. The author is not responsible for any damage to your Raspberry Pi, SD card, or other peripherals that may occur while following this guide.

What You'll Learn

  • Bare-metal programming: Writing code that runs directly on hardware without an existing OS
  • ARM64 assembly: Understanding the low-level architecture of the Raspberry Pi
  • Memory management: Controlling physical and virtual memory
  • Device drivers: Communicating with hardware like UART, GPIO, and timers
  • Process management: Implementing multitasking and scheduling
  • File systems: Reading and writing data to SD cards

Prerequisites

Required Knowledge

  • Basic C programming
  • Understanding of computer architecture
  • Familiarity with Linux command line
  • Git basics

Required Hardware

  • Raspberry Pi 4B (target platform)
  • SD Card (8GB or larger)
  • USB-to-TTL Serial Cable (for UART debugging)
  • PC/Mac (for development)

Software Tools

  • aarch64 cross-compiler (aarch64-linux-gnu-gcc)
  • CMake (build system)
  • Git (version control)

Course Roadmap

This series is organized into phases, building from basic hardware initialization to advanced OS features.

✅ Phase 1: Foundation

  1. Environment Setup - Setting up your development environment
  2. Boot Process - Understanding how the Raspberry Pi boots
  3. UART Hello World - Implementing serial communication
  4. System Timer - Precise timing and delays

✅ Phase 2: Hardware Control

  1. GPIO Control - Controlling LEDs and reading buttons
  2. Interrupts - Handling hardware interrupts and exceptions

✅ Phase 3: Display and Graphics

  1. Framebuffer - Drawing graphics to the screen
  2. Text Rendering - Rendering text on the framebuffer

✅ Phase 4: Memory Management

  1. Memory Allocation - Dynamic memory management (malloc/free)
  2. Virtual Memory (MMU) - Enabling caching and memory protection

✅ Phase 5: Process Management

  1. Context Switching - The foundation of multitasking
  2. Scheduler - Preemptive multitasking with time slicing

📋 Phase 6: Synchronization Primitives

  1. Synchronization Primitives - Mutexes, semaphores, and spinlocks (Race conditions, ARM64 atomic instructions)

📋 Phase 7: File Systems

  1. SD Card Driver - EMMC controller and block device abstraction
  2. FAT32 File System - Reading and writing files

📋 Phase 8: User Space

  1. User Space & System Calls - EL0/EL1 switching, System Calls, loading programs

Source Code Repository

All source code for this series is available at: /home/pa/src/simpian-os

Each article references specific files and explains their implementation details.

Progressive Feature Enablement

The OS supports building with features progressively enabled. This allows you to follow along with the articles and enable features as you learn:

1
2
3
4
5
# Build up to Article 08 (Text Rendering)
cmake -DENABLE_MEMORY_ALLOC=OFF \
      -DENABLE_MMU=OFF \
      -DENABLE_MULTITASKING=OFF ..
make

See README_FEATURES.md in the source repository for details.

Learning Path

Follow the articles in numerical order (01 → 12). This path provides early visual feedback and gradually introduces complexity.

Quick Start (Experienced Developers)

If you're already familiar with OS concepts, you can jump to specific topics: - Memory Management: Start at Article 09 - Multitasking: Start at Article 11 - Graphics: Start at Article 07

Getting Help

If you encounter issues: 1. Check the article's "Troubleshooting" section 2. Verify your hardware connections (especially UART) 3. Review the example code in the examples/ directory 4. Ensure your toolchain is correctly installed

Let's begin the journey of OS development!