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