# ARM64 Custom Operating System

## Folder Structure
```
os/
├── src/
│   ├── main.cpp
│   ├── kernel.cpp
│   ├── kernel.h
│   ├── memory/
│   │   ├── memory_manager.cpp
│   │   ├── memory_manager.h
│   │   └── page_tables.cpp
│   ├── cpu/
│   │   ├── cpu.cpp
│   │   ├── cpu.h
│   │   └── interrupts.cpp
│   ├── drivers/
│   │   ├── keyboard/
│   │   │   ├── keyboard.cpp
│   │   │   └── keyboard.h
│   │   ├── mouse/
│   │   │   ├── mouse.cpp
│   │   │   └── mouse.h
│   │   ├── video/
│   │   │   ├── video.cpp
│   │   │   └── video.h
│   │   ├── audio/
│   │   │   ├── audio.cpp
│   │   │   └── audio.h
│   │   ├── network/
│   │   │   ├── network.cpp
│   │   │   └── network.h
│   │   └── driver_manager.cpp
│   ├── filesystem/
│   │   ├── filesystem.cpp
│   │   └── filesystem.h
│   └── utils/
│       ├── string_utils.cpp
│       └── string_utils.h
├── include/
│   ├── config.h
│   └── types.h
├── linker.ld
├── Makefile
└── README.md
```

## Source Code

### src/main.cpp
```cpp
#include "kernel.h"

extern "C" void _start(void) {
    // Initialize the kernel
    kernel_init();
    
    // Main loop
    while (true) {
        // Kernel tasks
        kernel_tick();
    }
}
```

### src/kernel.cpp
```cpp
#include "kernel.h"
#include "../include/config.h"

// Forward declarations
extern "C" void kernel_init(void);
extern "C" void kernel_tick(void);

// Global variables
static bool kernel_initialized = false;

void kernel_init(void) {
    if (kernel_initialized) return;
    
    // Initialize memory manager
    memory_manager_init();
    
    // Initialize CPU
    cpu_init();
    
    // Initialize drivers
    driver_manager_init();
    
    // Initialize filesystem
    filesystem_init();
    
    // Initialize interrupts
    interrupts_init();
    
    // Enable interrupts
    __enable_irq();
    
    kernel_initialized = true;
}

void kernel_tick(void) {
    // Handle system tasks here
    if (!kernel_initialized) return;
    
    // Process keyboard input
    process_keyboard_input();
    
    // Process mouse input
    process_mouse_input();
    
    // Update display
    update_display();
    
    // Process network packets
    process_network_packets();
    
    // Update audio output
    update_audio_output();
}
```

### src/kernel.h
```cpp
#ifndef KERNEL_H
#define KERNEL_H

#include "../include/types.h"

// Kernel initialization
void kernel_init(void);
void kernel_tick(void);

// Memory management
void memory_manager_init(void);
void* alloc_memory(size_t size);
void free_memory(void* ptr);

// CPU operations
void cpu_init(void);
void __enable_irq(void);
void __disable_irq(void);

// Drivers
void driver_manager_init(void);
void process_keyboard_input(void);
void process_mouse_input(void);
void update_display(void);
void process_network_packets(void);
void update_audio_output(void);

// Filesystem
void filesystem_init(void);

// Interrupts
void interrupts_init(void);

#endif // KERNEL_H
```

### src/memory/memory_manager.cpp
```cpp
#include "memory_manager.h"
#include "../../include/types.h"

// Memory management structures
static uint8_t* heap_start = nullptr;
static uint8_t* heap_end = nullptr;
static size_t heap_size = 0;

// Simple first-fit allocator
struct HeapBlock {
    size_t size;
    bool is_free;
    HeapBlock* next;
};

static HeapBlock* block_list = nullptr;

void memory_manager_init(void) {
    // Initialize memory pool (this would typically be provided by the bootloader)
    heap_start = (uint8_t*)0x10000000;  // 256MB
    heap_end = (uint8_t*)0x20000000;   // 512MB
    heap_size = heap_end - heap_start;
    
    block_list = (HeapBlock*)heap_start;
    block_list->size = heap_size - sizeof(HeapBlock);
    block_list->is_free = true;
    block_list->next = nullptr;
}

void* alloc_memory(size_t size) {
    if (!block_list || size == 0) return nullptr;
    
    HeapBlock* current = block_list;
    HeapBlock* prev = nullptr;
    
    while (current != nullptr) {
        if (current->is_free && current->size >= size) {
            // Found a suitable block
            if (current->size > size + sizeof(HeapBlock)) {
                // Split the block
                HeapBlock* new_block = (HeapBlock*)((uint8_t*)current + sizeof(HeapBlock) + size);
                new_block->size = current->size - size - sizeof(HeapBlock);
                new_block->is_free = true;
                new_block->next = current->next;
                
                current->size = size;
                current->next = new_block;
            }
            
            current->is_free = false;
            return (void*)((uint8_t*)current + sizeof(HeapBlock));
        }
        
        prev = current;
        current = current->next;
    }
    
    return nullptr; // Out of memory
}

void free_memory(void* ptr) {
    if (!ptr) return;
    
    HeapBlock* block = (HeapBlock*)((uint8_t*)ptr - sizeof(HeapBlock));
    block->is_free = true;
    
    // Merge with next block if it's free
    if (block->next && block->next->is_free) {
        block->size += sizeof(HeapBlock) + block->next->size;
        block->next = block->next->next;
    }
}
```

### src/memory/memory_manager.h
```cpp
#ifndef MEMORY_MANAGER_H
#define MEMORY_MANAGER_H

#include "../../include/types.h"

void memory_manager_init(void);
void* alloc_memory(size_t size);
void free_memory(void* ptr);

#endif // MEMORY_MANAGER_H
```

### src/cpu/cpu.cpp
```cpp
#include "cpu.h"
#include "../../include/types.h"

// CPU initialization
void cpu_init(void) {
    // Set up CPU features (for ARM64)
    __asm__ volatile (
        "mov x0, #0x10\n\t"
        "msr sctlr_el1, x0\n\t"
        :
        :
        : "memory"
    );
}

void __enable_irq(void) {
    __asm__ volatile ("cpsie i" ::: "memory");
}

void __disable_irq(void) {
    __asm__ volatile ("cpsid i" ::: "memory");
}
```

### src/cpu/cpu.h
```cpp
#ifndef CPU_H
#define CPU_H

void cpu_init(void);
void __enable_irq(void);
void __disable_irq(void);

#endif // CPU_H
```

### src/drivers/keyboard/keyboard.cpp
```cpp
#include "keyboard.h"
#include "../../kernel.h"

// Keyboard state tracking
static bool key_states[256] = {false};
static char keyboard_buffer[256];
static int buffer_index = 0;

void keyboard_init(void) {
    // Initialize keyboard hardware
    // This would involve setting up interrupt handlers and configuring the PS/2 controller
}

void process_keyboard_input(void) {
    // Simulated keyboard input processing
    // In a real implementation, this would read from an actual keyboard controller
    
    // Check for new key presses (this is just a simulation)
    static int counter = 0;
    counter++;
    
    if (counter % 1000 == 0) {
        // Simulate typing 'Hello'
        if (buffer_index < 5) {
            keyboard_buffer[buffer_index] = "Hello"[buffer_index];
            buffer_index++;
        }
    }
}

// Get the current keyboard state
bool is_key_pressed(int key_code) {
    return key_states[key_code];
}

// Get a character from the keyboard buffer
char get_keyboard_char(void) {
    if (buffer_index > 0) {
        char ch = keyboard_buffer[0];
        // Shift buffer contents
        for (int i = 0; i < buffer_index - 1; i++) {
            keyboard_buffer[i] = keyboard_buffer[i + 1];
        }
        buffer_index--;
        return ch;
    }
    return 0;
}
```

### src/drivers/keyboard/keyboard.h
```cpp
#ifndef KEYBOARD_H
#define KEYBOARD_H

#include "../../include/types.h"

void keyboard_init(void);
void process_keyboard_input(void);
bool is_key_pressed(int key_code);
char get_keyboard_char(void);

#endif // KEYBOARD_H
```

### src/drivers/mouse/mouse.cpp
```cpp
#include "mouse.h"
#include "../../kernel.h"

// Mouse state tracking
struct MouseState {
    int x, y;
    bool left_button;
    bool right_button;
    bool middle_button;
};

static MouseState mouse_state = {0, 0, false, false, false};

void mouse_init(void) {
    // Initialize mouse hardware
    // This would involve setting up interrupt handlers and configuring the PS/2 controller
}

void process_mouse_input(void) {
    // Simulated mouse input processing
    
    static int counter = 0;
    counter++;
    
    if (counter % 500 == 0) {
        // Move mouse cursor around
        mouse_state.x += 1;
        mouse_state.y += 1;
        
        // Reset position after reaching boundary
        if (mouse_state.x > 800) mouse_state.x = 0;
        if (mouse_state.y > 600) mouse_state.y = 0;
    }
    
    // Simulate button presses
    if (counter % 1000 == 0) {
        mouse_state.left_button = !mouse_state.left_button;
    }
}

// Get current mouse position
void get_mouse_position(int* x, int* y) {
    *x = mouse_state.x;
    *y = mouse_state.y;
}

// Check if a button is pressed
bool is_left_button_pressed(void) {
    return mouse_state.left_button;
}

bool is_right_button_pressed(void) {
    return mouse_state.right_button;
}
```

### src/drivers/mouse/mouse.h
```cpp
#ifndef MOUSE_H
#define MOUSE_H

void mouse_init(void);
void process_mouse_input(void);
void get_mouse_position(int* x, int* y);
bool is_left_button_pressed(void);
bool is_right_button_pressed(void);

#endif // MOUSE_H
```

### src/drivers/video/video.cpp
```cpp
#include "video.h"
#include "../../kernel.h"

// Video memory and state
static uint32_t* video_buffer = nullptr;
static int screen_width = 800;
static int screen_height = 600;

void video_init(void) {
    // Initialize video hardware
    // This would involve setting up framebuffer or graphics mode
    
    // Allocate video buffer (this is just a simulation)
    video_buffer = (uint32_t*)0x40000000; // 1GB physical address
}

void update_display(void) {
    // Update display with current content
    // This would involve drawing from the frame buffer
    
    static int counter = 0;
    counter++;
    
    if (counter % 60 == 0) {
        // Clear screen
        for (int i = 0; i < screen_width * screen_height; i++) {
            video_buffer[i] = 0x000000FF; // Black with alpha channel
        }
        
        // Draw a simple rectangle in the center
        int rect_size = 100;
        int x_start = (screen_width - rect_size) / 2;
        int y_start = (screen_height - rect_size) / 2;
        
        for (int y = 0; y < rect_size; y++) {
            for (int x = 0; x < rect_size; x++) {
                if (x_start + x >= 0 && x_start + x < screen_width &&
                    y_start + y >= 0 && y_start + y < screen_height) {
                    int index = (y_start + y) * screen_width + (x_start + x);
                    video_buffer[index] = 0xFF00FF00; // Green
                }
            }
        }
    }
}

void draw_pixel(int x, int y, uint32_t color) {
    if (x >= 0 && x < screen_width && y >= 0 && y < screen_height) {
        video_buffer[y * screen_width + x] = color;
    }
}

void draw_rectangle(int x, int y, int width, int height, uint32_t color) {
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            draw_pixel(x + j, y + i, color);
        }
    }
}
```

### src/drivers/video/video.h
```cpp
#ifndef VIDEO_H
#define VIDEO_H

#include "../../include/types.h"

void video_init(void);
void update_display(void);
void draw_pixel(int x, int y, uint32_t color);
void draw_rectangle(int x, int y, int width, int height, uint32_t color);

#endif // VIDEO_H
```

### src/drivers/audio/audio.cpp
```cpp
#include "audio.h"
#include "../../kernel.h"

// Audio device state
static bool audio_initialized = false;
static uint16_t* audio_buffer = nullptr;

void audio_init(void) {
    // Initialize audio hardware
    // This would involve setting up DMA channels, sound cards, etc.
    
    audio_buffer = (uint16_t*)0x50000000; // 1.25GB physical address
    
    // Simulate initialization
    for (int i = 0; i < 44100; i++) {
        audio_buffer[i] = (i % 1000) * 10;
    }
    
    audio_initialized = true;
}

void update_audio_output(void) {
    if (!audio_initialized) return;
    
    // Simulate playing sound
    static int counter = 0;
    counter++;
    
    if (counter % 1000 == 0) {
        // Update audio buffer with new data (simplified)
        for (int i = 0; i < 44100; i++) {
            audio_buffer[i] = (i + counter) % 1000;
        }
    }
}

void play_sound(uint16_t* samples, size_t sample_count) {
    if (!audio_initialized || !samples) return;
    
    // Copy samples to audio buffer
    for (size_t i = 0; i < sample_count && i < 44100; i++) {
        audio_buffer[i] = samples[i];
    }
}
```

### src/drivers/audio/audio.h
```cpp
#ifndef AUDIO_H
#define AUDIO_H

#include "../../include/types.h"

void audio_init(void);
void update_audio_output(void);
void play_sound(uint16_t* samples, size_t sample_count);

#endif // AUDIO_H
```

### src/drivers/network/network.cpp
```cpp
#include "network.h"
#include "../../kernel.h"

// Network device state
static bool network_initialized = false;
static uint8_t* network_buffer = nullptr;

void network_init(void) {
    // Initialize network hardware
    // This would involve setting up Ethernet controllers, etc.
    
    network_buffer = (uint8_t*)0x60000000; // 1.5GB physical address
    
    // Simulate initialization
    for (int i = 0; i < 1500; i++) {
        network_buffer[i] = i % 256;
    }
    
    network_initialized = true;
}

void process_network_packets(void) {
    if (!network_initialized) return;
    
    // Simulate receiving packets
    static int counter = 0;
    counter++;
    
    if (counter % 1000 == 0) {
        // Process a simulated packet
        uint8_t* packet = network_buffer;
        packet[0] = 0x45; // IP header version
        packet[1] = 0x00; // IP header length
        packet[2] = 0x00; // Length high byte
        packet[3] = 0x40; // Length low byte
        
        // Simulate sending an ACK
        for (int i = 0; i < 1500; i++) {
            network_buffer[i] = (i + counter) % 256;
        }
    }
}

void send_packet(uint8_t* data, size_t length) {
    if (!network_initialized || !data || length == 0) return;
    
    // Copy packet to buffer
    for (size_t i = 0; i < length && i < 1500; i++) {
        network_buffer[i] = data[i];
    }
}

void receive_packet(uint8_t* buffer, size_t* length) {
    if (!network_initialized || !buffer || !length) return;
    
    // Copy from buffer to provided buffer
    for (size_t i = 0; i < *length && i < 1500; i++) {
        buffer[i] = network_buffer[i];
    }
}
```

### src/drivers/network/network.h
```cpp
#ifndef NETWORK_H
#define NETWORK_H

#include "../../include/types.h"

void network_init(void);
void process_network_packets(void);
void send_packet(uint8_t* data, size_t length);
void receive_packet(uint8_t* buffer, size_t* length);

#endif // NETWORK_H
```

### src/drivers/driver_manager.cpp
```cpp
#include "driver_manager.h"
#include "../kernel.h"

void driver_manager_init(void) {
    keyboard_init();
    mouse_init();
    video_init();
    audio_init();
    network_init();
}
```

### src/filesystem/filesystem.cpp
```cpp
#include "filesystem.h"
#include "../kernel.h"

void filesystem_init(void) {
    // Initialize file system structures
    // This would set up the root directory, mount points, etc.
}

// File operations (simplified)
int open_file(const char* filename) {
    // In a real implementation, this would look up the file in the filesystem
    return 0; // Simulated file descriptor
}

void read_file(int fd, void* buffer, size_t count) {
    // Read data from file into buffer
    for (size_t i = 0; i < count; i++) {
        ((uint8_t*)buffer)[i] = i % 256;
    }
}

void write_file(int fd, const void* buffer, size_t count) {
    // Write data from buffer to file
}
```

### src/filesystem/filesystem.h
```cpp
#ifndef FILESYSTEM_H
#define FILESYSTEM_H

#include "../include/types.h"

void filesystem_init(void);
int open_file(const char* filename);
void read_file(int fd, void* buffer, size_t count);
void write_file(int fd, const void* buffer, size_t count);

#endif // FILESYSTEM_H
```

### src/include/types.h
```c
#ifndef TYPES_H
#define TYPES_H

// Basic types for our OS kernel
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;
typedef unsigned long long uint64_t;

typedef signed char int8_t;
typedef signed short int16_t;
typedef signed int int32_t;
typedef signed long long int64_t;

#ifndef NULL
#define NULL ((void*)0)
#endif

#endif // TYPES_H
```

### Makefile
```makefile
CC = gcc
CFLAGS = -Wall -Wextra -std=c99 -O2 -ffreestanding -fno-builtin -nostdlib -nostartfiles -nodefaultlibs
LDFLAGS = -T linker.ld -static

# Source files
SOURCES = src/kernel.c \
          src/drivers/video/video.c \
          src/drivers/audio/audio.c \
          src/drivers/network/network.c \
          src/drivers/mouse/mouse.c \
          src/drivers/driver_manager.c \
          src/filesystem/filesystem.c

OBJECTS = $(SOURCES:.c=.o)

# Default target
all: kernel.bin

# Link the kernel
kernel.bin: $(OBJECTS)
	ld $(LDFLAGS) -o kernel.bin $(OBJECTS)

# Compile source files
%.o: %.c
	$(CC) $(CFLAGS) -c $< -o $@

clean:
	rm -f $(OBJECTS) kernel.bin

.PHONY: all clean
```

### linker.ld
```ld
ENTRY(_start)

SECTIONS
{
    . = 0x100000;
    
    .text : {
        *(.text)
    }
    
    .rodata : {
        *(.rodata)
    }
    
    .data : {
        *(.data)
    }
    
    .bss : {
        *(.bss)
    }
}
```

This is a simplified kernel framework that demonstrates how to structure an operating system kernel with drivers for video, audio, network, and input devices. The implementation includes:

1. Basic OS structure with drivers for different hardware components
2. Memory management concepts through physical addresses
3. Device initialization and processing functions
4. File system integration (simplified)
5. Compilation and linking setup

The code is designed to be modular and extensible, showing how a real OS would organize its components. Each driver can be expanded with more sophisticated functionality as needed for a complete operating system implementation.

Note: This is a conceptual framework and not a fully functional OS - it's meant to demonstrate structure and organization rather than provide a working kernel. In practice, such an implementation would require much more complexity in each component and proper integration with hardware abstraction layers.