_    _      _             _           _        
        /\ \/_/\    /\ \          /\ \        / /\      
       /  \ \ \ \   \ \_\        /  \ \      / /  \     
      / /\ \ \ \ \__/ / /       / /\ \ \    / / /\ \__  
     / / /\ \_\ \__ \/_/       / / /\ \ \  / / /\ \___\ 
    / / /_/ / /\/_/\__/\      / / /  \ \_\ \ \ \ \/___/ 
   / / /__\/ /  _/\/__\ \    / / /   / / /  \ \ \       
  / / /_____/  / _/_/\ \ \  / / /   / / /    \ \ \      
 / / /        / / /   \ \ \/ / /___/ / /_/\__/ / /      
/ / /        / / /    /_/ / / /____\/ /\ \/___/ /       
\/_/         \/_/     \_\/\/_________/  \_____\/        
                                                        

PXOS Kernel

A 32-bit x86 operating system kernel written in C and assembly, featuring a modular architecture with process management, memory management, filesystem support, and an interactive shell.

Architecture

• Target Architecture: x86-32 (32-bit protected mode)
• Bootloader: Custom assembly bootloader that loads the kernel from floppy disk
• Memory Model: Protected mode with paging support
• Display: VGA text mode (80x25)

Core Components

Component	Description	Key Features
Boot System	Assembly bootloader	Real mode → Protected mode, GDT setup
Memory Management	Virtual memory & paging	4KB pages, heap allocation, memory tracking
Process Management	Process scheduling	PCB, 5 states, 4 priorities, context switching, time slice rotation, process aging
Interrupt System	Hardware/software interrupts	IDT, x86 exceptions, system calls (int 0x80)
File System	FAT12 filesystem	File/directory ops, simulation mode*
Device Drivers	Hardware interfaces	VGA display, PS/2 keyboard
Interactive Shell	Command interface	20+ built-in commands, full CLI
Library Functions	Utility functions	String/memory operations

*File system is in simulation mode - no actual disk I/O

File Structure

oskernel/
├── arch/x86/           # x86 architecture specific code
│   ├── boot.asm        # Bootloader
│   ├── interrupt_asm.asm
│   ├── paging_asm_simple.asm
│   ├── syscall_asm.asm
│   └── context_switch.asm # Process context switching
├── drivers/            # Device drivers
│   ├── vga/           # VGA display driver
│   └── keyboard/      # Keyboard driver
├── fs/                # File system
│   ├── filesystem.c
│   └── filesystem.h
├── kernel/            # Core kernel
│   ├── kernel.c       # Main kernel and shell
│   ├── interrupt.c    # Interrupt handling
│   ├── memory.c       # Memory management
│   ├── syscall.c      # System call implementation
│   └── process/       # Process management
├── lib/               # Library functions
│   ├── string.c
│   └── string.h
├── linker.ld          # Linker script
└── Makefile          # Build system

Running the Kernel

1. Build the kernel: make clean && make all
2. Run in QEMU: make run
3. The kernel will boot and present an interactive shell

Technical Specifications

• Memory Layout:
  • Kernel starts at 0x100000 (1MB)
  • Kernel heap at 0x200000 (2MB)
  • User space starts at 0x400000 (4MB)
• Page Size: 4KB
• Maximum Processes: 64
• Process Scheduling:
  • Time slice rotation with configurable quantum
  • Process aging mechanism to prevent starvation
  • 4 priority levels: Low, Normal, High, Critical
  • 5 process states: New, Ready, Running, Blocked, Terminated
• File System: FAT12 with 512-byte sectors
• Display: VGA text mode 80x25
• Interrupts: x86 exception handling + timer/keyboard + system calls
• Timer Frequency: 100Hz (10ms intervals)