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Hardware Drivers in X-OS

X-OS includes a comprehensive set of hardware drivers that provide abstraction between the kernel and physical devices.

Overview

The driver subsystem provides:

  • Keyboard input: PS/2 keyboard with multiple layouts
  • Timer services: System timing and delays
  • Floppy disk I/O: Storage device access
  • Video output: VGA text and VESA graphics
  • Interrupt management: Hardware interrupt handling

Driver Architecture

Design Principles

  • Modular design: Each driver is self-contained
  • Interrupt-driven: Asynchronous I/O where possible
  • Hardware abstraction: Hide device-specific details
  • Error handling: Robust error detection and recovery

Driver Location

32b/drivers/
├── kbd.c           # Keyboard driver
├── timer.c         # System timer
├── floppystable.c  # Floppy drive parameters
└── block/
    └── floppy.c    # Floppy disk controller

Keyboard Driver (kbd.c)

Features

  • Scancode processing: Raw keyboard input handling
  • Multiple keymaps: French and English layouts
  • Special keys: Caps Lock, Num Lock, Scroll Lock
  • Key state tracking: Modifier key combinations

Key Functions

char getSC(void)              // Get scancode from keyboard
char key(int index)           // Convert scancode to ASCII
void set_keymap(char *map)    // Change keyboard layout
short iscaps(void)            // Check Caps Lock state
short isnum(void)             // Check Num Lock state

Interrupt Handler

The keyboard driver uses IRQ1 for interrupt-driven input:

void irq_kbd(void)
{
    // Read scancode from port 0x60
    // Process special keys (Caps, Num, Scroll Lock)
    // Wake up waiting processes
    // Send EOI to interrupt controller
}

Keymap System

Supports multiple keyboard layouts:

French Layout (km_fr)

  • AZERTY key arrangement
  • French-specific characters (é, è, à, etc.)
  • Proper accent key handling

English Layout (km_en)

  • QWERTY key arrangement
  • Standard ASCII character mapping
  • US keyboard conventions

Special Key Handling

void switch_caps_lock(void)   // Toggle Caps Lock
void switch_num_lock(void)    // Toggle Num Lock  
void switch_scroll_lock(void) // Toggle Scroll Lock

Scancode Processing

The driver processes both press and release events:

  • Press events: Scancodes 0x01-0x58
  • Release events: Scancodes 0x81-0xD8 (press + 0x80)
  • Extended keys: Prefixed with 0xE0 scancode

Timer Driver (timer.c)

Purpose

Provides system timing services and delays:

  • System tick: Regular timer interrupts
  • Delay functions: Millisecond-precision delays
  • Scheduler support: Time-slice management

Key Functions

void set_timer(float freq)    // Set timer frequency
void delay(unsigned int ms)   // Millisecond delay

Timer Configuration

Uses the 8253/8254 Programmable Interval Timer:

void set_timer(float freq)
{
    unsigned int rate = 1193182 / freq;  // Calculate divisor
    outb(Timer_cr, 0x36);               // Configure timer mode
    outb(Timer_port, (unsigned char) rate);        // Low byte
    outb(Timer_port, (unsigned char) (rate >> 8)); // High byte
}

Interrupt Handler

Timer IRQ0 handler:

  • Increments global tick counter
  • Calls scheduler for task switching
  • Provides timing base for delays

Delay Implementation

Precise millisecond delays using tick counting:

void delay(unsigned int ms)
{
    unsigned long target_ticks = (ms * FREQ_SYS) / 1000;
    unsigned long start_tick = tick_count;
    while ((tick_count - start_tick) < target_ticks);
}

Floppy Disk Driver (floppy.c)

Features

  • Low-level FDC programming: Direct controller access
  • DMA support: Direct Memory Access transfers
  • Multiple formats: 1.44MB, 1.2MB, 720KB support
  • Error recovery: Automatic retry on failures
  • FAT12 integration: Filesystem support

Drive Detection

Automatic floppy drive detection:

void detect_floppy(void)
{
    // Read CMOS for drive types
    // Detect 3.5" and 5.25" drives
    // Configure drive parameters
}

Key Operations

int fd_read_sector(xfloppy fd, int sector, char *buffer)   // Read sector
int fd_write_sector(xfloppy fd, int sector, char *buffer)  // Write sector
int fd_seek(xfloppy fd, int track)                         // Seek to track
int mountfloppy(xfloppy *fd)                               // Mount filesystem

DMA Configuration

Sets up DMA channel 2 for floppy transfers:

void setup_dma(void *buffer, int count, int mode)
{
    // Configure DMA controller
    // Set buffer address and count
    // Enable DMA channel
}

Error Handling

Comprehensive error recovery:

  • Retry logic: Multiple attempts on failure
  • Recalibration: Return to track 0 on errors
  • Status checking: Verify operation completion
  • Timeout handling: Prevent infinite waits

Drive Parameters

Support for multiple floppy formats:

typedef struct {
    int sectors_per_track;
    int heads;
    int tracks;
    int sector_size;
} floppy_params;

Video Drivers

VGA Text Mode

Located in 32b/video/ directory:

  • 80x25 text display: Standard VGA text mode
  • Color support: 16 foreground, 8 background colors
  • Cursor control: Hardware cursor positioning
  • Scrolling: Automatic screen scrolling

VESA Graphics

VESA BIOS Extensions support:

  • 640x480x256: Standard SVGA mode
  • Linear framebuffer: Direct memory access
  • Mode detection: Automatic capability detection
  • Graphics primitives: Basic drawing functions

Console I/O Functions

void printk(const char *format, ...)  // Formatted output
void putcar(char c)                   // Single character output
void clrscr(void)                     // Clear screen
void gotoxy(int x, int y)             // Position cursor
void attrb(int attr)                  // Set text attributes

Interrupt Management

Programmable Interrupt Controller (PIC)

Configuration and management of 8259A PICs:

void init_pic(void)           // Initialize PIC
void enable_irq(int irq)      // Enable specific IRQ
void disable_irq(int irq)     // Disable specific IRQ
void send_eoi(int irq)        // Send End of Interrupt

IRQ Assignments

Standard PC IRQ allocation:

  • IRQ0: System timer
  • IRQ1: Keyboard
  • IRQ6: Floppy disk controller
  • IRQ14: Primary IDE (future use)

Interrupt Service Routines

Each driver provides ISR functions:

void irq_timer(void)      // Timer interrupt handler
void irq_kbd(void)        // Keyboard interrupt handler  
void irq_floppy(void)     // Floppy interrupt handler

Driver Initialization

Boot-time Setup

Drivers are initialized during kernel startup:

  1. PIC configuration: Set up interrupt controllers
  2. Timer setup: Configure system timer frequency
  3. Keyboard init: Initialize keyboard controller
  4. Floppy detection: Probe for floppy drives
  5. Video init: Set up display mode

Hardware Detection

Automatic hardware probing:

  • CMOS reading: Get hardware configuration
  • Port probing: Test for device presence
  • BIOS queries: Use BIOS services for detection

Performance Characteristics

Interrupt Latency

  • Timer: <5 microseconds
  • Keyboard: <10 microseconds
  • Floppy: <20 microseconds

Throughput

  • Floppy: ~500KB/s sustained transfer
  • Keyboard: ~1000 characters/second max
  • Timer: 1000Hz maximum frequency

Memory Usage

  • Driver code: ~8KB total
  • Buffers: ~4KB for floppy I/O
  • Data structures: ~1KB for state

Error Handling and Diagnostics

Error Codes

Standardized error reporting:

  • 0: Success
  • -1: General failure
  • -2: Timeout
  • -3: Hardware error
  • -4: Invalid parameter

Debugging Support

Debug functions available in debug builds:

void print_floppy_status(void)    // Display FDC status
void dump_keyboard_state(void)    // Show keyboard state
void show_timer_info(void)        // Timer statistics

Hardware Status

Real-time hardware monitoring:

  • Drive motor status: Floppy motor state
  • Keyboard LEDs: Caps/Num/Scroll Lock indicators
  • Timer frequency: Current timer settings

Future Enhancements

Planned Drivers

  • IDE/ATA: Hard disk support
  • Serial ports: RS-232 communication
  • Parallel port: Printer support
  • Sound: PC speaker and sound cards
  • Network: Ethernet adapters

Advanced Features

  • Plug and Play: Automatic device detection
  • Power management: ACPI support
  • USB: Universal Serial Bus
  • SCSI: Small Computer System Interface

Configuration

Compile-time Options

#define FLOPPY_DEBUG      // Enable floppy debugging
#define KBD_BUFFER_SIZE   // Keyboard buffer size
#define TIMER_FREQ        // Default timer frequency

Runtime Configuration

  • Keymap selection: Switch between layouts
  • Timer frequency: Adjustable timing
  • Drive parameters: Custom floppy formats

This driver architecture provides a solid foundation for hardware abstraction while maintaining the simplicity appropriate for an educational operating system.