Implement Keyboard Interrupt in MultiBoot Bootloader

Implementing keyboard support in your kernel involves setting up an Interrupt Service Routine (ISR) for the keyboard, which is typically connected to IRQ1.

1. Update the ISR table
   1. First, we need to add a handler for the keyboard interrupt (IRQ1).
2. Keyboard Handler
   1. Create a handler function for the keyboard interrupt.
3. Install the keyboard handler
   1. Install the keyboard handler in the kernel_main function.
4. Update the IRQ Stubs in Assembly

1 keyboard.c

#include <system.h>

/* 
 * US Keyboard layout mapping scancodes to ASCII characters.
 * This array maps the scancodes from the keyboard to the corresponding characters.
 */
char kbd_us[128] = {
    0, 27,            // 0x00: No key, 0x01: ESC
    '1','2','3','4','5','6','7','8','9','0', // 0x02-0x0B: Number keys
    '-','=','\b',     // 0x0C-0x0E: '-', '=', Backspace
    '\t',             // 0x0F: Tab
    'q','w','e','r','t','y','u','i','o','p', // 0x10-0x19: Alphabet keys
    '[',']','\n',     // 0x1A-0x1C: '[', ']', Enter
    0,                // 0x1D: Control
    'a','s','d','f','g','h','j','k','l',';', // 0x1E-0x26: Alphabet keys
    '\'', '`',        // 0x27-0x28: '\'', '`'
    0,                // 0x29: Left shift
    '\\','z','x','c','v','b','n','m',',','.','/', // 0x2A-0x35: Alphabet keys and symbols
    0,                // 0x36: Right shift
    '*',              // 0x37: Keypad '*'
    0,                // 0x38: Alt
    ' ',              // 0x39: Space
    0,                // 0x3A: Caps lock
    0,                // 0x3B: F1
    0, 0, 0, 0, 0, 0, 0, 0, // 0x3C-0x43: F2-F10 (not mapped)
    0,                // 0x44: Num lock
    0,                // 0x45: Scroll lock
    0,                // 0x46: Home
    0,                // 0x47: Up arrow
    0,                // 0x48: Page up
    '-',              // 0x49: Keypad '-'
    0,                // 0x4A: Left arrow
    0,                // 0x4B: (empty)
    0,                // 0x4C: Right arrow
    '+',              // 0x4D: Keypad '+'
    0,                // 0x4E: End
    0,                // 0x4F: Down arrow
    0,                // 0x50: Page down
    0,                // 0x51: Insert
    0,                // 0x52: Delete
    0, 0, 0,          // 0x53-0x55: (empty)
    0,                // 0x56: F11
    0,                // 0x57: F12
    0                 // 0x58-0x7F: (everything else)
};

/*
 * Keyboard interrupt handler.
 * This function handles keyboard interrupts, reads the scancode from the keyboard,
 * and translates it into an ASCII character using the kbd_us array.
 */
void keyboard_handler(struct regs *r) {
    unsigned char scancode;

    // Read the scancode from the keyboard's data buffer
    scancode = inportb(0x60);

    if (scancode & 0x80) {
        // If the highest bit of the scancode is set, it's a key release event (key up).
        // We ignore these events in this simple implementation.
    } else {
        // If the highest bit is not set, it's a key press event (key down).
        // We convert the scancode to an ASCII character and print it to the screen.
        putch(kbd_us[scancode]);
    }
}

/*
 * Install the keyboard handler.
 * This function installs the keyboard_handler function as the IRQ1 handler.
 */
void keyboard_install() {
    // Install the keyboard handler for IRQ1 (keyboard interrupt)
    irq_install_handler(1, keyboard_handler);
}

/*
 * Wait for the keyboard controller to be ready.
 * This function waits until the keyboard controller is ready to send or receive data.
 */
void keyboard_wait() {
    // Wait until the keyboard controller's input buffer is clear
    while(inportb(0x64) & 2);
}

Explanation:

• kbd_us array: Maps keyboard scancodes to ASCII characters. Only some keys are mapped for simplicity.
• keyboard_handler function: Handles keyboard interrupts. Reads the scancode, and if it's a key press (not a key release), it prints the corresponding character.
• keyboard_install function: Installs keyboard_handler as the handler for IRQ1 (the keyboard interrupt).
• keyboard_wait function: Waits for the keyboard controller to be ready to send or receive data.

2 Update system.h

Implement keyboard function extern declarations.

/* Keyboard */
extern void keyboard_install();
extern void keyboard_wait();

3 Modify kernel main function

We have to call keyboard_install() function from the kernel main.

keyboard_install();

Output