KritiOs

The project’s Goal to learn and implement concepts of Operating systems and create a toy UNIX type 32 bit OS from scratch which includes The bootloader, drivers and some basic functionality.

Tools Used

The Project utilizes NASM Assembly Compiler for assembly compilations and GCC Cross Compiler (elf-i386) to compile C code for 32 Bit machines. For virtualization and testing, qemu was used. Linux’s make command was also utilized for hassle free compilations.

The project was also tested on a spare laptop without any OS installed, which worked fine.

Modules

The Bootloader

A bootloader, also known as a boot program or bootstrap loader, is a special operating system software that loads into the working memory of a computer after start-up. Our Bootloader is divided into three parts -

• Boot.asm - Greets the user and loads the loader.asm. We have kept the loader on a different memory location for better memory management.
• Loader.asm - It loads the kernel on the memory, loads the Global Descriptor Table, switches to 32 Bits and Jump to the Kernel.
• Routines - These are some common functions which are used throughout the bootloader, for example print in real mode and wait for user input.

The Kernel

I have divided kernel into 4 parts.

• Drivers - It contains all the drivers including the video and keyboard drivers.
• Cpu - It contains functions related to CPU like handling interrupts.
• General - This file contains general functions which are required throughout the kernel, like memcpy, reverse etc
• Kernel.c - The main kernel file which is loaded when we boot our OS.

Running

The easiest way of running the hard disk image (boot.img) is QEMU. Since KritiOs is a 32-bit operating system, the emulator used is qemu-system-i386, it should come inside the qemu-system-x86 package, and also other packages that include it like qemu-emulators-full.

Then, run the following command:

qemu-system-i386 -drive file=boot.img,format=raw -soundhw pcspk

Gallery

References

This project was made possible by the OSDevWiki: https://wiki.osdev.org & this repo: https://github.com/cfenollosa/os-tutorial