Mini Operating System for x86 PCs

Overview

This project consists of developing a mini operating system (n7OS) for x86 PCs, written in C and assembly.
The goal is to understand and implement the core mechanisms of an operating system from scratch.

Objectives

What we will cover

• Basic I/O management (keyboard and screen)
• Interrupt handling
• Process management
• Virtual memory management for processes

What we will not cover

• File system management
• Resource sharing and inter-process communication

Covered topics

Starter

• Console display
• Interrupt management
• System calls

Topics:

• Console implementation
• write system call

Main Course

• Timer management
• Process creation and destruction
• Scheduling and round-robin execution

Topics:

• Timer interrupt
• Process scheduling and management

Dessert

• Keyboard input
• Command interpreter

Topics:

• Keyboard reading and read system call
• Simple shell implementation

Tools Setup

Compilation

sudo apt-get install build-essential

Execution

sudo apt-get install qemu

Debugging

sudo apt-get install gdb

GDB connects to QEMU to help detect and analyze potential issues.

Note

Commands are for Debian and derivatives (I use Ubuntu). Adapt based on your Linux distribution. On Mac: Use x86 gcc tools via macports (package i386-elf-gcc).

The Amuse-Bouches

Project Structure

• /boot
  • Boot directory;
  • crt0.S initializes hardware and starts the main system program (kernel_start)
• /kernel
  • Kernel source directory
  • This is where most things will happen
• /lib
  • Some useful tools (e.g., printf)
• /include
  • For .h files

Getting Started with the Environment

• Compilation via make command
  • If all goes well, result: kernel.bin
• Execution: make run
  • A QEMU window should appear
  • The system runs
• Debugging
  • Launch: make dbg
  • Set breakpoint at system start: b kernel_start
  • Run execution: cont or r
  • Display a variable: display variable name
  • n: Next, s: Step

Usage

Compilation

make

Result : kernel.bin

Run

make run

A QEMU window should appear and the OS will start.

Debugging

make dbg

Then inside GDB:

b kernel_start     # Set breakpoint at system start
cont or r          # Run
display <variable> # Show variable value
n                  # Next
s                  # Step into

Demo

OS commands

help

This command prints the available commands.

Runner Game

run runner

This command starts the runner game.

Snake Game

run snake

This command starts the snake game.