Someone can explain this IDT [0x21] in the indexes of these structs
Why does 0x21 tell us?
struct IDT_entry IDT[IDT_SIZE];
unsigned long keyboard_address;
unsigned long idt_address;
unsigned long idt_ptr[2];
/* populate IDT entry of keyboard's interrupt */
keyboard_address = (unsigned long)keyboard_handler;
IDT[0x21].offset_lowerbits = keyboard_address & 0xffff;
IDT[0x21].selector = 0x08; /* KERNEL_CODE_SEGMENT_OFFSET */
IDT[0x21].zero = 0;
IDT[0x21].type_attr = 0x8e; /* INTERRUPT_GATE */
IDT[0x21].offset_higherbits = (keyboard_address & 0xffff0000) >> 16;