Make your own OS in 30 days – day6: GDT/IDT and Keyboard/Mouse interrupts

Day6 describes the following 3 which are necessary to receive data from keyboard & mouse.
* GDT; Global Dispatch Table
* IDT; Interrupt Dispatch Table
* PIC; Programmable Interrupt Controller

Here is an int21 handler for keyboard interrupts. It has a similar mouse handler. It only shows the pre-defined message and halts after receiving the first key. It won’t show mouse data since it hasn’t reset interrupt handlers to receive more interrupts (mouse interrupt is not 1 byte).

Since interrupt handler should end with ‘IRETD’ instead of ‘RET’, it’s not fully written in C, but written in asm (_asm_inthandler21) which calls _inthandler21 written in C.

		EXTERN	_inthandler21, _inthandler27, _inthandler2c

_asm_inthandler21:
		PUSH	ES
		PUSH	DS
		PUSHAD
		MOV		EAX,ESP
		PUSH	EAX
		MOV		AX,SS
		MOV		DS,AX
		MOV		ES,AX
		CALL	_inthandler21
		POP		EAX
		POPAD
		POP		DS
		POP		ES
		IRETD

void inthandler21(int *esp)
{
  struct BOOTINFO *binfo = (struct BOOTINFO *)ADR_BOOTINFO;
  boxfill8(binfo->vram, binfo->scrnx, COL8_000000, 0, 0, 32 * 8 - 1, 15);
  putfonts8_asc(binfo->vram, binfo->scrnx, 0, 0, COL8_FFFFFF,
                "INT 21 (IRQ-1) : PS/2 keyboard");
  for (;;) {
    io_hlt();
  }
}

Day 07 will get key codes and mouse data.