Keyboard driver

Overview

The keyboard driver handles input from the PS/2 keyboard, translates raw scancodes into ASCII characters, and keeps track of the current modifier state (Shift, Ctrl, AltGr).

It relies on the PS/2 controller for low-level communication and uses IRQ1 to receive keyboard events.

Scancode handling

  • The driver supports Set 1 scancodes (as configured by the PS/2 controller).
  • Scancodes are read via port 0x60.
  • A key press sends a “make” code.
  • A key release sends a “break” code (make code + 0x80).

Keymaps

There are two lookup tables:

  • keyboard_map_normal: standard ASCII for non-shifted keys.
  • keyboard_map_shift: uppercase/symbols for when Shift is active.
// Example: 'a' key
keyboard_map_normal[0x1E] = 'a';
keyboard_map_shift[0x1E]   = 'A';

Modifier keys

The driver keeps track of:

  • Shift (K_LEFT_SHIFT, K_RIGHT_SHIFT)
  • Ctrl (K_CTRL)
  • AltGr (K_ALTGR)

Each of them toggles a flag (e.g., shift_pressed), updated depending on whether the scancode is a make or break.

Functions

kbd_read_scancode()

uint8_t kbd_read_scancode();

Reads the latest scancode from port 0x60.

kbd_scancode_to_char(uint8_t scancode)

char kbd_scancode_to_char(uint8_t scancode);
  • Takes a scancode (from kbd_read_scancode()).
  • Updates modifier key states.
  • Returns the corresponding ASCII character, or 0 if:
  • It was a modifier key
  • It's a break code
  • It's an unrecognized key

Dependencies

  • PS/2 controller: receives raw scancodes via IRQ1
  • I/O ports: read scancodes from 0x60
  • PIC: IRQ1 routing
  • Console (if output is needed elsewhere)

Notes

  • The driver does not include a key buffer (FIFO) or blocking getchar() yet.