README.md

Tiny OS Development Project

This project focuses on creating a minimal operating system that can boot, execute simple C functions, and display text using a framebuffer driver. It follows Worksheet 2 Part 1 and references The Little Book of OS Development.

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1. Project Overview

The project's primary objectives are:

1. Develop a bootloader to load the kernel.
2. Transition from assembly to C for kernel functionality.
3. Implement a framebuffer driver for text output, cursor positioning, and screen clearing.
4. Test the operating system in QEMU and document the outcomes.

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2. Directory Structure

The directory structure is organized as follows:

tiny-os/
├── source/
│   ├── loader.asm   # Bootloader in assembly
│   ├── kernel.c     # Main kernel logic
│   ├── fb.c         # Framebuffer driver
│   ├── io.c         # Low-level I/O functions
│   └── link.ld      # Linker script
├── include/
│   ├── fb.h         # Framebuffer driver header
│   └── io.h         # I/O functions header
├── iso/
│   └── boot/
│       └── grub/
│           ├── stage2_eltorito # GRUB bootloader file
│           └── menu.lst        # GRUB configuration
├── Makefile        # Automates build processes
└── README.md       # Project documentation

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## **3.Features**

Key features of this project include:

1. Bootloader:
- GRUB is used to load the kernel.
- The kernel starts execution at the entry point defined in loader.asm.
2. Transition to C:
- The kernel successfully calls and executes functions implemented in kernel.c.
3.Framebuffer Driver:
- Implements the following functions:
  -fb_clear(): Clears the screen.
  -fb_print(): Prints text at specified row and column.
  -fb_move(): Moves the cursor to a specific position.
4.QEMU Testing:
-The OS is tested using QEMU in graphical and curses modes.

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## **4. Implementation Details**

Bootloader (loader.asm)
The bootloader adheres to the Multiboot specification and transfers control to the kernel:

```asm
global loader
extern kernel_main

section .text
align 4

MAGIC_NUMBER equ 0x1BADB002
FLAGS equ 0x0
CHECKSUM equ -MAGIC_NUMBER

dd MAGIC_NUMBER
dd FLAGS
dd CHECKSUM

loader:
    call kernel_main
    hlt

Kernel (kernel.c) The kernel initializes the framebuffer and tests its driver:

#include "fb.h"

void kernel_main() {
    fb_clear();
    fb_print("Sum: 6", 0, 0);
    fb_print("Booting Tiny OS", 1, 0);
    fb_move(2, 0);
    while (1) {}
}

Framebuffer Driver (fb.c) Implements APIs for interacting with the framebuffer:

#include "fb.h"
#include "io.h"

void fb_clear() {
    char *fb = (char *)0xB8000;
    for (int i = 0; i < 80 * 25; i++) {
        fb[i * 2] = ' ';
        fb[i * 2 + 1] = 0x07;
    }
}

void fb_print(const char *str, unsigned short row, unsigned short col) {
    char *fb = (char *)0xB8000;
    unsigned short pos = (row * 80 + col) * 2;
    for (int i = 0; str[i] != '\0'; i++) {
        fb[pos + i * 2] = str[i];
        fb[pos + i * 2 + 1] = 0x07;
    }
}

void fb_move(unsigned short row, unsigned short col) {
    unsigned short pos = row * 80 + col;
    outb(0x3D4, 0x0F);
    outb(0x3D5, (unsigned char)(pos & 0xFF));
    outb(0x3D4, 0x0E);
    outb(0x3D5, (unsigned char)((pos >> 8) & 0xFF));
}

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5. Build and Run Instructions

1. Clean the Build Directory

make clean