dos33fsprogs/games/keen/longer_sound.s
2024-04-04 00:14:27 -04:00

49 lines
987 B
ArmAsm

; Based on redbook_sound.s
; it's originally by Paul Lutus, from the Apple II Red Book p45
; which can only do roughly 194Hz to 2000Hz+
; this makes things twice as long, which allows lower notes, but
; loses some precision on high notes
; also modified so "0" means no sound
;=====================================================
; speaker tone
;=====================================================
; A,X,Y trashed
; duration also trashed
; more exactly, it is (4+10F)+(13+10F) = 20F+17
speaker_tone:
ldy #0 ; 3
speaker_tone_loop:
lda $C030 ; click speaker ; 4
speaker_loop:
nop
nop
nop
nop
nop
dey ; ; 2
bne freq_loop ; ; 2/3
dec speaker_duration ; (Duration) ; 6
beq done_tone ; 2/3
freq_loop:
dex ; 2
bne speaker_loop ; 2/3
ldx speaker_frequency ; (Frequency) ; 4
beq speaker_loop ; play nothing if 0 ; 2/3
jmp speaker_tone_loop ; 3
done_tone:
rts
speaker_duration:
.byte $00
speaker_frequency:
.byte $00