org 0x100
cpu 8086
bits 16

section .code

setup:
	; Save original video mode
	mov ah, 0xf
	int 0x10
	mov [original_video_mode], al

	; Move to VGA 320x200 256 color mode
	mov ah, 0
	mov al, 0x13
	int 0x10

	; Set es to point to VGA framebuffer
	mov ax, 0xa000
	mov es, ax

mainloop:
	mov ah, 0x2c
	int 0x21
	cmp ch, [hour]
	jne .changed
	cmp cl, [minute]
	jne .changed
	cmp dh, [second]
	jne .changed
	jmp .unchanged

	.changed:
		call clear_screen

		mov [hour], ch
		mov [minute], cl
		mov [second], dh

		mov bp, 0
		add bp, [hour]
		mov byte [es:bp], 1

		mov bp, [width]
		add bp, [minute]
		mov byte [es:bp], 2

		mov bp, [width]
		add bp, [width]
		add bp, [second]
		mov byte [es:bp], 4

	.unchanged:
	hlt
	jmp mainloop

exit:
	; Restore video mode
	mov ah, 0
	mov al, [original_video_mode]
	int 0x10

	ret

clear_screen:
	push bp

	xor bp, bp
	.loop:
		mov word [es:bp], 0
		inc bp
		cmp bp, 320*200/2
		jne .loop

	pop bp
	ret

section .rodata
width dw 320
height dw 200

section .data
hour dw 0
minute dw 0
second dw 0

original_video_mode db 0