Apollo-RTOS

An AGC-Inspired Real-Time Operating System for Embedded Systems

   _____         _ _        _____ _____ _____ _____
  |  _  |___ ___| | |___   | __  |_   _|     |   __|
  |     | . | . | | | . |  |    -| | | |  |  |__   |
  |__|__|  _|___|_|_|___|  |__|__| |_| |_____|_____|
        |_|

  Welcome to Apollo RTOS!

  boot level: boot
  stats: n_flash = 124, n_boot = 7, n_power = 6, n_reset = 99

  >> help
  pkill   htop    help    prof    accel   show
  calc    clear   echo    cat     ls      touch
  rm      heart

  >> 

Overview

Apollo-RTOS is a real-time operating system designed for the BBC micro:bit v1. Inspired by the Apollo Guidance Computer (AGC) — the computer that powered the Apollo 11 moon landing — this project reimagines its resilient, restart-based architecture in a modern embedded context.

Despite operating in a drastically more powerful environment than the AGC (2 MHz, 4 KB RAM), embedded systems today still face core challenges: real-time responsiveness, fault tolerance, resource efficiency, and system recovery. Apollo-RTOS revisits historical design principles and merges them with modern C++20 features and Unix philosophies to build a robust, modular, and highly maintainable operating system.

Key features include:

• Hybrid cooperative-preemptive scheduler supporting up to 16 concurrent processes
• Restart-based fault recovery ensuring resilience against resets and power failures
• Persistent file systems unifying Flash and FRAM memory
• Unix-like shell interface for interacting with processes, files, and system status
• Dynamic memory management and modular drivers (UART, I2C, Display)
• Automated testing framework for system verification
• C++20 clean, type-safe, template-driven implementation

Apollo-RTOS demonstrates that principles developed for the Apollo missions still hold value today, offering a blueprint for modern embedded system reliability under tight resource constraints.

Motivation

• Historical Legacy: The AGC demonstrated revolutionary reliability strategies under severe hardware limitations. Learning from its design teaches timeless engineering principles.
• Modern Application: Embedded devices, though more powerful today, still require extreme reliability with minimal resources, especially in safety-critical and mission-critical systems.
• Educational: Building Apollo-RTOS from scratch offers a practical exercise in real-time system design, low-level embedded programming, and C++ systems engineering.

Target Device

BBC micro:bit v1

• ARM Cortex-M0 CPU
• 16 KB RAM, 256 KB Flash
• 5x5 LED display
• Serial over USB
• I2C bus for external FRAM support (optional)

Requirements

Hardware

• BBC micro:bit v1
• (Optional) I2C FRAM chip (e.g., Fujitsu MB85RC256V) for persistent storage testing
• USB cable to flash firmware onto the micro:bit

Software

• Toolchain:
  • arm-none-eabi-gcc (for cross-compiling)
  • arm-none-eabi-g++
  • arm-none-eabi-objcopy
  • arm-none-eabi-objdump
• CMake (>= 2.8)
• Python 3 (for post-build scripts like stack usage analysis)
• Minicom (for UART communication over USB)
• (Optional) QEMU (for emulation/testing without hardware)

Install gcc-arm-none-eabi, cmake, python3, and minicom via your system package manager.

Building the Project

1. Clone the repository:

git clone https://github.com/AnglyPascal/apollo-rtos.git
cd apollo-rtos

2. Create a build directory:

mkdir build && cd build

3. Configure CMake:

cmake ..

4. Build the project:

make apollo

This will generate the apollo.hex file ready to flash onto your micro:bit.

Flashing to the micro:bit

1. Connect your micro:bit via USB.
2. Copy the generated HEX file:

cp apollo.hex /media/<your-username>/MICROBIT/

Alternatively, enable automatic copying by setting the COPY_HEX CMake option:

cmake -DCOPY_HEX=ON ..
make apollo

Running and Interacting

• After flashing, open a serial connection:

minicom -D /dev/ttyACM0 -b 9600

• You will be greeted with the Apollo-RTOS shell:

 _____         _ _        _____ _____ _____ _____
|  _  |___ ___| | |___   | __  |_   _|     |   __|
|     | . | . | | | . |  |    -| | | |  |  |__   |
|__|__|  _|___|_|_|___|  |__|__| |_| |_____|_____|
    |_|

Welcome to Apollo RTOS!

boot level: boot
stats: n_flash = 23, n_boot = 5, n_power = 3, n_reset = 33

>>

You can then run built-in commands, manage processes, inspect system stats, and interact with files.

Emulating (Optional)

If you prefer not to use hardware:

• Run Apollo-RTOS inside QEMU:

make qemu

• For debugging with GDB:

make qemu-gdb

Project Structure

• src/ - Core OS code: scheduler, memory management, drivers, file systems, shell
• include/ - Header files
• tests/ - Unit tests and system tests
• scripts/ - Helper scripts (e.g., flashing, stack usage analysis)

License

This project is open for educational and experimental purposes. For more information, please refer to the repository's LICENSE file.