org 51000

counter EQU inc_counter + 1
attrs EQU #5800
xylo EQU attrs + 40

zero_counter:
	xor a

set_counter:
	ld (counter), a

read_keyboard:
	ld a, #f7
	in a, (#fe)
	rra
	jr nc, key_1
	rra
	jr nc, key_2
	rra
	jr nc, key_3
	rra
	jr nc, key_4
	rra
	jr c, read_keyboard

key_5:
	ld de, #040C
	jr invoke

key_2:
	ld de, #0103
	jr invoke

key_3:
	ld de, #0206
	jr invoke

key_4:
	ld de, #0309
	jr invoke

key_1:
	ld de, #0000
invoke:
	push de
	call highlight_key
	ld a, (counter)
	add a, d
	call play
	pop de
	call highlight_key

inc_counter:
	ld a, 0		;This value will be modified by the running code
	add a, 5
	cp 25
	jr nz, set_counter
	jr zero_counter

highlight_key:
	ld hl, xylo
	push de
	ld d, 0
	add hl, de
	ld e, 30
	ld a, (hl)
	xor %01000000
	ld b, 15
highlight_block:
	ld (hl), a
	inc hl
	ld (hl), a
	inc hl
	ld (hl), a
	add hl, de
	djnz highlight_block
	pop de
	ret

INCLUDE "sample.asm"