Game 1 Unit 13 of 64 1 hr learning time

Sound Effects

Add APU sound effects for collection and death.

20% of Neon Nexus

Mark as complete Completed!

What You’re Building

Sound. The game comes alive.

Sound Effects

Collect an item: ascending beep. Hit an enemy: descending warble.

The APU

The NES Audio Processing Unit has 5 channels:

2 pulse waves (square waves)
1 triangle wave
1 noise channel
1 DMC (sample playback)

We use pulse channel 1 for simple sound effects.

APU Registers

APUSTATUS = $4015         ; Enable channels
APU_PULSE1_CTRL = $4000   ; Volume, duty cycle
APU_PULSE1_SWEEP = $4001  ; Frequency sweep
APU_PULSE1_LO = $4002     ; Period low byte
APU_PULSE1_HI = $4003     ; Period high, length

Collection Sound

A short, high-pitched beep:

play_collect_sound:
    lda #%10011111      ; 50% duty, constant vol, vol 15
    sta APU_PULSE1_CTRL
    lda #0
    sta APU_PULSE1_SWEEP
    lda #$C4            ; Period low (high pitch)
    sta APU_PULSE1_LO
    lda #%00001000      ; Period high, trigger
    sta APU_PULSE1_HI
    rts

Death Sound

A descending tone using the sweep unit:

play_death_sound:
    lda #%10011111      ; 50% duty, vol 15
    sta APU_PULSE1_CTRL
    lda #%10001111      ; Sweep down, fast
    sta APU_PULSE1_SWEEP
    lda #$00            ; Start low pitch
    sta APU_PULSE1_LO
    lda #%00001011      ; Trigger
    sta APU_PULSE1_HI
    rts

The sweep unit automatically decreases the frequency, creating a falling sound.

The Code

; =============================================================================
; NEON NEXUS - Unit 13: Sound Effects
; =============================================================================
; Add APU sound effects for collection and death.
; =============================================================================

PPUCTRL   = $2000
PPUMASK   = $2001
PPUSTATUS = $2002
OAMADDR   = $2003
PPUSCROLL = $2005
PPUADDR   = $2006
PPUDATA   = $2007
OAMDMA    = $4014
APUSTATUS = $4015
JOYPAD1   = $4016

; APU Pulse 1 registers
APU_PULSE1_CTRL = $4000
APU_PULSE1_SWEEP = $4001
APU_PULSE1_LO = $4002
APU_PULSE1_HI = $4003

BTN_UP     = %00001000
BTN_DOWN   = %00000100
BTN_LEFT   = %00000010
BTN_RIGHT  = %00000001

PLAYER_START_X  = 124
PLAYER_START_Y  = 116
PLAYER_SPEED    = 2
ENEMY_SPEED     = 1
NUM_ENEMIES     = 4
NUM_ITEMS       = 4
STARTING_LIVES  = 3
COLLISION_DIST  = 6
COLLECT_DIST    = 8
INVULN_TIME     = 90

TILE_BORDER    = 1
TILE_FLOOR     = 2
TILE_CORNER_TL = 3
TILE_CORNER_TR = 4
TILE_CORNER_BL = 5
TILE_CORNER_BR = 6
SPRITE_PLAYER  = 7
SPRITE_ENEMY   = 8
SPRITE_LIFE    = 9
SPRITE_ITEM    = 10

ARENA_LEFT   = 16
ARENA_RIGHT  = 232
ARENA_TOP    = 24
ARENA_BOTTOM = 208

DIR_RIGHT = 1
DIR_LEFT  = $FF
DIR_DOWN  = 1
DIR_UP    = $FF
BG_COLOUR = $0F

.segment "ZEROPAGE"
player_x:       .res 1
player_y:       .res 1
buttons:        .res 1
temp:           .res 1
row_counter:    .res 1
frame_count:    .res 1
lives:          .res 1
invuln_timer:   .res 1
game_over:      .res 1
items_collected: .res 1
score_lo:       .res 1     ; Score low byte
score_hi:       .res 1     ; Score high byte (for scores > 255)

enemy_x:        .res NUM_ENEMIES
enemy_y:        .res NUM_ENEMIES
enemy_dir_x:    .res NUM_ENEMIES
enemy_dir_y:    .res NUM_ENEMIES

item_x:         .res NUM_ITEMS
item_y:         .res NUM_ITEMS
item_active:    .res NUM_ITEMS   ; Non-zero if item exists

.segment "OAM"
oam_buffer:     .res 256

.segment "BSS"

.segment "HEADER"
    .byte "NES", $1A, 2, 1, $01, $00, 0,0,0,0,0,0,0,0

.segment "CODE"

reset:
    sei
    cld
    ldx #$40
    stx $4017
    ldx #$FF
    txs
    inx
    stx PPUCTRL
    stx PPUMASK
    stx $4010

@vblank1:
    bit PPUSTATUS
    bpl @vblank1

    lda #0
@clear_ram:
    sta $0000, x
    sta $0100, x
    sta $0200, x
    sta $0300, x
    sta $0400, x
    sta $0500, x
    sta $0600, x
    sta $0700, x
    inx
    bne @clear_ram

@vblank2:
    bit PPUSTATUS
    bpl @vblank2

    jsr load_palette
    jsr draw_arena
    jsr set_attributes
    jsr init_game

    lda #$FF
    ldx #0
@hide_all:
    sta oam_buffer, x
    inx
    bne @hide_all

    jsr update_all_sprites

    lda #0
    sta PPUSCROLL
    sta PPUSCROLL

    ; Enable APU channels
    lda #%00000001      ; Enable pulse 1
    sta APUSTATUS

    lda #%10000000
    sta PPUCTRL
    lda #%00011110
    sta PPUMASK

main_loop:
    lda game_over
    bne @game_over_loop
    jsr read_controller
    jsr move_player
    jsr move_enemies
    jsr check_enemy_collisions
    jsr check_item_collisions
    jsr update_all_sprites
    jmp main_loop

@game_over_loop:
    jmp @game_over_loop

init_game:
    lda #STARTING_LIVES
    sta lives
    lda #0
    sta game_over
    sta invuln_timer
    sta items_collected
    sta score_lo
    sta score_hi

    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    jsr init_enemies
    jsr init_items
    rts

init_enemies:
    lda #48
    sta enemy_x+0
    sta enemy_y+0
    lda #DIR_RIGHT
    sta enemy_dir_x+0
    lda #DIR_DOWN
    sta enemy_dir_y+0

    lda #200
    sta enemy_x+1
    lda #48
    sta enemy_y+1
    lda #DIR_LEFT
    sta enemy_dir_x+1
    lda #DIR_DOWN
    sta enemy_dir_y+1

    lda #48
    sta enemy_x+2
    lda #176
    sta enemy_y+2
    lda #DIR_RIGHT
    sta enemy_dir_x+2
    lda #DIR_UP
    sta enemy_dir_y+2

    lda #200
    sta enemy_x+3
    lda #176
    sta enemy_y+3
    lda #DIR_LEFT
    sta enemy_dir_x+3
    lda #DIR_UP
    sta enemy_dir_y+3
    rts

init_items:
    ; Place 4 items around the arena
    lda #80
    sta item_x+0
    lda #64
    sta item_y+0
    lda #1
    sta item_active+0

    lda #168
    sta item_x+1
    lda #64
    sta item_y+1
    lda #1
    sta item_active+1

    lda #80
    sta item_x+2
    lda #160
    sta item_y+2
    lda #1
    sta item_active+2

    lda #168
    sta item_x+3
    lda #160
    sta item_y+3
    lda #1
    sta item_active+3
    rts

check_enemy_collisions:
    lda invuln_timer
    beq @check
    dec invuln_timer
    rts

@check:
    ldx #0
@check_enemy:
    lda player_x
    sec
    sbc enemy_x, x
    bpl @check_x_pos
    eor #$FF
    clc
    adc #1
@check_x_pos:
    cmp #COLLISION_DIST
    bcs @next_enemy

    lda player_y
    sec
    sbc enemy_y, x
    bpl @check_y_pos
    eor #$FF
    clc
    adc #1
@check_y_pos:
    cmp #COLLISION_DIST
    bcs @next_enemy

    jsr player_hit
    rts

@next_enemy:
    inx
    cpx #NUM_ENEMIES
    bne @check_enemy
    rts

check_item_collisions:
    ldx #0
@check_item:
    lda item_active, x
    beq @next_item

    lda player_x
    sec
    sbc item_x, x
    bpl @item_x_pos
    eor #$FF
    clc
    adc #1
@item_x_pos:
    cmp #COLLECT_DIST
    bcs @next_item

    lda player_y
    sec
    sbc item_y, x
    bpl @item_y_pos
    eor #$FF
    clc
    adc #1
@item_y_pos:
    cmp #COLLECT_DIST
    bcs @next_item

    ; Collected! Add 100 points
    lda #0
    sta item_active, x
    inc items_collected
    ; Add 100 to score (100 = $64)
    lda score_lo
    clc
    adc #100
    sta score_lo
    lda score_hi
    adc #0
    sta score_hi
    jsr play_collect_sound

@next_item:
    inx
    cpx #NUM_ITEMS
    bne @check_item
    rts

player_hit:
    jsr play_death_sound
    dec lives
    lda lives
    beq @game_over

    lda #PLAYER_START_X
    sta player_x
    lda #PLAYER_START_Y
    sta player_y

    lda #INVULN_TIME
    sta invuln_timer
    rts

@game_over:
    lda #1
    sta game_over
    rts

; -----------------------------------------------------------------------------
; Sound Effects
; -----------------------------------------------------------------------------
play_collect_sound:
    ; High-pitched short beep
    lda #%10011111      ; Duty 50%, length counter disabled, constant vol, vol 15
    sta APU_PULSE1_CTRL
    lda #0
    sta APU_PULSE1_SWEEP
    lda #$C4            ; Low byte of period (high pitch)
    sta APU_PULSE1_LO
    lda #%00001000      ; Length counter load, high bits of period
    sta APU_PULSE1_HI
    rts

play_death_sound:
    ; Low-pitched descending sound
    lda #%10011111      ; Duty 50%, constant vol, vol 15
    sta APU_PULSE1_CTRL
    lda #%10001111      ; Sweep enabled, down, fast
    sta APU_PULSE1_SWEEP
    lda #$00            ; Low byte of period (low pitch)
    sta APU_PULSE1_LO
    lda #%00001011      ; Length counter load, high bits
    sta APU_PULSE1_HI
    rts

update_all_sprites:
    jsr update_player_sprite
    jsr update_enemy_sprites
    jsr update_item_sprites
    jsr update_lives_display
    rts

update_player_sprite:
    lda game_over
    beq @alive
    lda #$FF
    sta oam_buffer+0
    rts

@alive:
    lda invuln_timer
    beq @show
    and #%00000100
    beq @show
    lda #$FF
    sta oam_buffer+0
    rts

@show:
    lda player_y
    sta oam_buffer+0
    lda #SPRITE_PLAYER
    sta oam_buffer+1
    lda #0
    sta oam_buffer+2
    lda player_x
    sta oam_buffer+3
    rts

update_enemy_sprites:
    ldx #0
    ldy #4
@loop:
    lda enemy_y, x
    sta oam_buffer, y
    iny
    lda #SPRITE_ENEMY
    sta oam_buffer, y
    iny
    lda #%00000001
    sta oam_buffer, y
    iny
    lda enemy_x, x
    sta oam_buffer, y
    iny
    inx
    cpx #NUM_ENEMIES
    bne @loop
    rts

update_item_sprites:
    ldx #0
    ldy #20             ; OAM offset after enemies
@loop:
    lda item_active, x
    beq @hide_item

    lda item_y, x
    sta oam_buffer, y
    iny
    lda #SPRITE_ITEM
    sta oam_buffer, y
    iny
    lda #%00000010      ; Palette 2 (green)
    sta oam_buffer, y
    iny
    lda item_x, x
    sta oam_buffer, y
    iny
    jmp @next_item

@hide_item:
    lda #$FF
    sta oam_buffer, y
    iny
    iny
    iny
    iny

@next_item:
    inx
    cpx #NUM_ITEMS
    bne @loop
    rts

update_lives_display:
    ldy #36             ; OAM offset for lives
    ldx lives
    beq @hide_all

    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #16
    sta oam_buffer, y
    iny

    cpx #1
    beq @hide_rest

    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #26
    sta oam_buffer, y
    iny

    cpx #2
    beq @hide_rest

    lda #8
    sta oam_buffer, y
    iny
    lda #SPRITE_LIFE
    sta oam_buffer, y
    iny
    lda #0
    sta oam_buffer, y
    iny
    lda #36
    sta oam_buffer, y
    rts

@hide_rest:
@hide_all:
    rts

move_enemies:
    ldx #0
@enemy_loop:
    lda enemy_x, x
    clc
    adc enemy_dir_x, x
    sta enemy_x, x
    cmp #ARENA_LEFT
    bcs @check_right
    lda #DIR_RIGHT
    sta enemy_dir_x, x
    lda #ARENA_LEFT
    sta enemy_x, x
    jmp @move_y
@check_right:
    cmp #ARENA_RIGHT
    bcc @move_y
    lda #DIR_LEFT
    sta enemy_dir_x, x
    lda #ARENA_RIGHT
    sec
    sbc #1
    sta enemy_x, x
@move_y:
    lda enemy_y, x
    clc
    adc enemy_dir_y, x
    sta enemy_y, x
    cmp #ARENA_TOP
    bcs @check_bottom
    lda #DIR_DOWN
    sta enemy_dir_y, x
    lda #ARENA_TOP
    sta enemy_y, x
    jmp @next_enemy
@check_bottom:
    cmp #ARENA_BOTTOM
    bcc @next_enemy
    lda #DIR_UP
    sta enemy_dir_y, x
    lda #ARENA_BOTTOM
    sec
    sbc #1
    sta enemy_y, x
@next_enemy:
    inx
    cpx #NUM_ENEMIES
    bne @enemy_loop
    rts

load_palette:
    bit PPUSTATUS
    lda #$3F
    sta PPUADDR
    lda #$00
    sta PPUADDR
    ldx #0
@loop:
    lda palette_data, x
    sta PPUDATA
    inx
    cpx #32
    bne @loop
    rts

draw_arena:
    bit PPUSTATUS
    lda #$20
    sta PPUADDR
    lda #$00
    sta PPUADDR
    lda #0
    sta row_counter
@draw_row:
    lda row_counter
    cmp #0
    beq @top_row
    cmp #1
    beq @top_row
    cmp #28
    beq @bottom_row
    cmp #29
    beq @bottom_row
    jmp @middle_row
@top_row:
    lda row_counter
    cmp #0
    bne @top_row_inner
    lda #TILE_CORNER_TL
    sta PPUDATA
    lda #TILE_BORDER
    ldx #30
@top_fill:
    sta PPUDATA
    dex
    bne @top_fill
    lda #TILE_CORNER_TR
    sta PPUDATA
    jmp @next_row
@top_row_inner:
    lda #TILE_BORDER
    ldx #32
@top_inner_fill:
    sta PPUDATA
    dex
    bne @top_inner_fill
    jmp @next_row
@bottom_row:
    lda row_counter
    cmp #29
    bne @bottom_row_inner
    lda #TILE_CORNER_BL
    sta PPUDATA
    lda #TILE_BORDER
    ldx #30
@bottom_fill:
    sta PPUDATA
    dex
    bne @bottom_fill
    lda #TILE_CORNER_BR
    sta PPUDATA
    jmp @next_row
@bottom_row_inner:
    lda #TILE_BORDER
    ldx #32
@bottom_inner_fill:
    sta PPUDATA
    dex
    bne @bottom_inner_fill
    jmp @next_row
@middle_row:
    lda #TILE_BORDER
    sta PPUDATA
    sta PPUDATA
    lda #TILE_FLOOR
    ldx #28
@floor_fill:
    sta PPUDATA
    dex
    bne @floor_fill
    lda #TILE_BORDER
    sta PPUDATA
    sta PPUDATA
@next_row:
    inc row_counter
    lda row_counter
    cmp #30
    beq @done_drawing
    jmp @draw_row
@done_drawing:
    rts

set_attributes:
    bit PPUSTATUS
    lda #$23
    sta PPUADDR
    lda #$C0
    sta PPUADDR
    ldx #8
    lda #$00
@attr_top:
    sta PPUDATA
    dex
    bne @attr_top
    ldx #6
@attr_floor:
    lda #$00
    sta PPUDATA
    lda #%01010101
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    sta PPUDATA
    lda #$00
    sta PPUDATA
    dex
    bne @attr_floor
    ldx #8
    lda #$00
@attr_bottom:
    sta PPUDATA
    dex
    bne @attr_bottom
    rts

read_controller:
    lda #1
    sta JOYPAD1
    lda #0
    sta JOYPAD1
    ldx #8
@read_loop:
    lda JOYPAD1
    lsr a
    rol buttons
    dex
    bne @read_loop
    rts

move_player:
    lda buttons
    and #BTN_UP
    beq @check_down
    lda player_y
    sec
    sbc #PLAYER_SPEED
    cmp #ARENA_TOP
    bcc @check_down
    sta player_y
@check_down:
    lda buttons
    and #BTN_DOWN
    beq @check_left
    lda player_y
    clc
    adc #PLAYER_SPEED
    cmp #ARENA_BOTTOM
    bcs @check_left
    sta player_y
@check_left:
    lda buttons
    and #BTN_LEFT
    beq @check_right
    lda player_x
    sec
    sbc #PLAYER_SPEED
    cmp #ARENA_LEFT
    bcc @check_right
    sta player_x
@check_right:
    lda buttons
    and #BTN_RIGHT
    beq @done
    lda player_x
    clc
    adc #PLAYER_SPEED
    cmp #ARENA_RIGHT
    bcs @done
    sta player_x
@done:
    rts

nmi:
    pha
    txa
    pha
    tya
    pha
    lda #0
    sta OAMADDR
    lda #>oam_buffer
    sta OAMDMA
    inc frame_count
    lda #0
    sta PPUSCROLL
    sta PPUSCROLL
    pla
    tay
    pla
    tax
    pla
    rti

irq:
    rti

palette_data:
    .byte BG_COLOUR, $11, $21, $31
    .byte BG_COLOUR, $13, $23, $33
    .byte BG_COLOUR, $19, $29, $39
    .byte BG_COLOUR, $16, $26, $36
    .byte BG_COLOUR, $30, $27, $17    ; Player
    .byte BG_COLOUR, $16, $26, $36    ; Enemies
    .byte BG_COLOUR, $1A, $2A, $3A    ; Items (green)
    .byte BG_COLOUR, $30, $27, $17

.segment "VECTORS"
    .word nmi
    .word reset
    .word irq

.segment "CHARS"
.byte $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
.byte %11111111,%10000001,%10000001,%11111111,%11111111,%00010001,%00010001,%11111111
.byte %00000000,%01111110,%01111110,%00000000,%00000000,%11101110,%11101110,%00000000
.byte %00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%10000001
.byte %00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%00000000,%00000000
.byte %11111111,%11000000,%10100000,%10010000,%10001000,%10000100,%10000010,%10000001
.byte %00000000,%00111111,%01011111,%01101111,%01110111,%01111011,%01111101,%01111110
.byte %11111111,%00000011,%00000101,%00001001,%00010001,%00100001,%01000001,%10000001
.byte %00000000,%11111100,%11111010,%11110110,%11101110,%11011110,%10111110,%01111110
.byte %10000001,%10000010,%10000100,%10001000,%10010000,%10100000,%11000000,%11111111
.byte %01111110,%01111101,%01111011,%01110111,%01101111,%01011111,%00111111,%00000000
.byte %10000001,%01000001,%00100001,%00010001,%00001001,%00000101,%00000011,%11111111
.byte %01111110,%10111110,%11011110,%11101110,%11110110,%11111010,%11111100,%00000000
.byte %00011000,%00011000,%00111100,%01111110,%11111111,%10111101,%00100100,%00100100
.byte %00000000,%00011000,%00011000,%00111100,%01000010,%01000010,%00011000,%00000000
.byte %00011000,%00111100,%01111110,%11111111,%11111111,%01111110,%00111100,%00011000
.byte %00000000,%00011000,%00100100,%01000010,%01000010,%00100100,%00011000,%00000000
.byte %00000000,%00100100,%01111110,%01111110,%00111100,%00011000,%00000000,%00000000
.byte %00000000,%00000000,%00000000,%00100100,%00011000,%00000000,%00000000,%00000000
; Tile 10: Item (data core - diamond)
.byte %00000000,%00011000,%00111100,%01111110,%01111110,%00111100,%00011000,%00000000
.byte %00000000,%00000000,%00011000,%00100100,%00100100,%00011000,%00000000,%00000000

.res 8192 - 176, $00

Build It

ca65 nexus.asm -o nexus.o
ld65 -C nes.cfg nexus.o -o nexus.nes

The game now has audio feedback. Actions have sounds.

Collecting items is satisfying, but there’s no goal. Unit 14 adds a win condition.

What Changed

Unit 12 → Unit 13

+42-2

1	1		`; =============================================================================`
2		-	`; NEON NEXUS - Unit 12: Scoring`
	2	+	`; NEON NEXUS - Unit 13: Sound Effects`
3	3		`; =============================================================================`
4		-	`; Add a score that increases when collecting items.`
	4	+	`; Add APU sound effects for collection and death.`
5	5		`; =============================================================================`
6	6
7	7		`PPUCTRL = $2000`
			...
12	12		`PPUADDR = $2006`
13	13		`PPUDATA = $2007`
14	14		`OAMDMA = $4014`
	15	+	`APUSTATUS = $4015`
15	16		`JOYPAD1 = $4016`
	17	+
	18	+	`; APU Pulse 1 registers`
	19	+	`APU_PULSE1_CTRL = $4000`
	20	+	`APU_PULSE1_SWEEP = $4001`
	21	+	`APU_PULSE1_LO = $4002`
	22	+	`APU_PULSE1_HI = $4003`
16	23
17	24		`BTN_UP = %00001000`
18	25		`BTN_DOWN = %00000100`
			...
135	142		`lda #0`
136	143		`sta PPUSCROLL`
137	144		`sta PPUSCROLL`
	145	+
	146	+	`; Enable APU channels`
	147	+	`lda #%00000001 ; Enable pulse 1`
	148	+	`sta APUSTATUS`
138	149
139	150		`lda #%10000000`
140	151		`sta PPUCTRL`
			...
322	333		`lda score_hi`
323	334		`adc #0`
324	335		`sta score_hi`
	336	+	`jsr play_collect_sound`
325	337
326	338		`@next_item:`
327	339		`inx`
			...
330	342		`rts`
331	343
332	344		`player_hit:`
	345	+	`jsr play_death_sound`
333	346		`dec lives`
334	347		`lda lives`
335	348		`beq @game_over`
			...
346	359		`@game_over:`
347	360		`lda #1`
348	361		`sta game_over`
	362	+	`rts`
	363	+
	364	+	`; -----------------------------------------------------------------------------`
	365	+	`; Sound Effects`
	366	+	`; -----------------------------------------------------------------------------`
	367	+	`play_collect_sound:`
	368	+	`; High-pitched short beep`
	369	+	`lda #%10011111 ; Duty 50%, length counter disabled, constant vol, vol 15`
	370	+	`sta APU_PULSE1_CTRL`
	371	+	`lda #0`
	372	+	`sta APU_PULSE1_SWEEP`
	373	+	`lda #$C4 ; Low byte of period (high pitch)`
	374	+	`sta APU_PULSE1_LO`
	375	+	`lda #%00001000 ; Length counter load, high bits of period`
	376	+	`sta APU_PULSE1_HI`
	377	+	`rts`
	378	+
	379	+	`play_death_sound:`
	380	+	`; Low-pitched descending sound`
	381	+	`lda #%10011111 ; Duty 50%, constant vol, vol 15`
	382	+	`sta APU_PULSE1_CTRL`
	383	+	`lda #%10001111 ; Sweep enabled, down, fast`
	384	+	`sta APU_PULSE1_SWEEP`
	385	+	`lda #$00 ; Low byte of period (low pitch)`
	386	+	`sta APU_PULSE1_LO`
	387	+	`lda #%00001011 ; Length counter load, high bits`
	388	+	`sta APU_PULSE1_HI`
349	389		`rts`
350	390
351	391		`update_all_sprites:`