OS Project - Real Process Scheduling

Overview

This is a simple operating system built from scratch that demonstrates preemptive multitasking with a round-robin process scheduler. The OS is compiled using a cross-compiler and boots using QEMU.

Features

• VGA Text Mode Display - 80x25 terminal with color support and scrolling
• Process Scheduling - Preemptive round-robin scheduler with time slicing
• Context Switching - Simulated process context switches with visual indicators
• Multiple Processes - Demonstrates scheduling of 4 processes (ProcessA, ProcessB, ProcessC, IdleProc)
• Timer Interrupts - Programmable Interval Timer (PIT) for scheduling decisions

Prerequisites

Before running this project, make sure you have the following installed on your Linux system:

• Docker - Used to build the cross-compilation environment using gcc-cross-i686-elf docker image
• QEMU - Required to run the OS kernel (qemu-system-i386)
• GRUB tools - For multiboot verification

How to Run

To run the project run the following commands in a Linux OS:

make
make run

What it does

1. make - Builds a Docker container with the i686 cross-compilation toolchain and compiles the kernel
2. make run - Runs the compiled kernel using QEMU emulator

The OS will display:

• A greeting message
• Process scheduling demonstration with colored output:
  • Green A's - ProcessA executing
  • Blue B's - ProcessB executing
  • Red C's - ProcessC executing
  • Gray dots - Idle process executing
  • Pipes (|) - Context switch indicators
• Scheduling statistics (total context switches)

Build Process

The build process involves:

1. Creating a Docker environment with i686-elf cross-compiler
2. Assembling the boot loader (boot.s)
3. Compiling the kernel (kernel.c)
4. Compiling the scheduler (scheduler.c)
5. Linking everything together with the custom linker script
6. Verifying multiboot compliance

Project Structure

.
├── boot.s           # Assembly bootloader (multiboot compliant)
├── kernel.c         # Main kernel with VGA terminal functions
├── scheduler.c      # Process scheduler implementation
├── scheduler.h      # Scheduler header and data structures
├── linker.ld        # Linker script for memory layout
├── makefile         # Build automation
└── buildenv/        # Docker build environment
    └── Dockerfile

OS Concepts Demonstrated

• Process Control Block (PCB) - Stores process state, stack pointers, and metadata
• Round-Robin Scheduling - Fair CPU time distribution with time slicing
• Preemptive Multitasking - Processes can be interrupted by timer
• Context Switching - Switching between processes
• Process States - READY, RUNNING, BLOCKED, TERMINATED

Authors

By Abhinav Pant and Cavin Monis