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Keyboard System

The keyboard system manages keyboard input through interrupt handling and provides a high-level interface for getting user input. It handles raw keyboard events, scancode translation, and input buffering.

Features​

  • Interrupt-based keyboard handling
  • US QWERTY keyboard mapping
  • Input buffering with backspace support
  • Python-style input() functionality
  • Configurable input buffer size

Hardware Interface​

The keyboard controller interfaces with:

  • Keyboard Data Port: 0x60
  • Keyboard Status Port: 0x64
  • Interrupt Request Line: IRQ1

API Reference​

Initialization​

bool idt_init(void)​

Initializes the Interrupt Descriptor Table (IDT) for keyboard handling.

Features:

  • Sets up keyboard interrupt handler (IRQ1)
  • Configures the Programmable Interrupt Controller (PIC)
  • Returns true when initialization is successful

void kb_init(void)​

Enables keyboard interrupts.

Features:

  • Enables IRQ1 (keyboard interrupt)
  • Should be called after idt_init()

Input Functions​

char* get_input(const char* prompt = nullptr)​

Gets a line of input from the keyboard, similar to Python's input() function.

Parameters:

  • prompt: Optional string to display before getting input

Features:

  • Blocks until Enter key is pressed
  • Supports backspace for editing
  • Input is limited to MAX_INPUT_LENGTH characters (256 by default)
  • Returns null-terminated string containing the user's input

Control Functions​

void kb_disable(void)​

Disables keyboard interrupts.

Features:

  • Disables all interrupts on the primary PIC
  • Useful for system shutdown or when keyboard input needs to be temporarily disabled

Implementation Details​

Keyboard Map​

The system uses a US QWERTY keyboard map that translates scan codes to ASCII characters:

  • Letters (a-z)
  • Numbers (0-9)
  • Special characters (-, =, [, ], etc.)
  • Control keys (backspace, tab, enter)

Interrupt Handling​

  1. IDT Configuration

    • Uses IDT entry 0x21 for keyboard interrupt
    • Sets up interrupt gate with proper privileges

  2. PIC Configuration

    • Programs the 8259 PIC
    • Enables only keyboard interrupts (IRQ1)
    • Handles interrupt acknowledgment

  3. Input Processing

    • Reads scan code from keyboard port
    • Translates scan code to ASCII
    • Handles special keys
    • Updates input buffer

Input Buffer​

  • Static buffer with 256-character capacity
  • Maintains current position and input state
  • Handles backspace by moving position backward
  • Automatically null-terminates strings

Usage Examples​

// Initialize keyboard system
if (!keyboard::idt_init()) {
    display::print("Keyboard initialization failed\n");
    return;
}

// Get input with a prompt
char* name = keyboard::get_input("Enter your name: ");

// Get input without a prompt
char* command = keyboard::get_input();

// Disable keyboard when done
keyboard::kb_disable();

Limitations​

  • US QWERTY layout only
  • No support for:
    • Function keys (F1-F12)
    • Modifier keys (Shift, Ctrl, Alt)
    • Special keys (Insert, Delete, etc.)
  • Fixed input buffer size (256 characters)
  • Blocking input only (no non-blocking mode)

Error Handling​

The keyboard system includes basic error handling:

  • Initialization failure detection
  • Buffer overflow prevention
  • Invalid scan code filtering
  • Basic input validation

Hardware Requirements​

  • Standard PS/2 keyboard controller
  • Intel 8259 PIC
  • x86 processor with interrupt support