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40 lines
1.2 KiB
ArmAsm
40 lines
1.2 KiB
ArmAsm
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; Mariano Domínguez
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; 2022-12-4
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; this file provides an equivalent to the BASIC SOUND function
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; void __fastcall__ _sound (unsigned char voice, unsigned char frequency, unsigned char distortion, unsigned char volume);
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;
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.include "atari.inc"
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.export __sound
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.import popa
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.importzp tmp1,tmp2
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; play sound, arguments: voice, pitch, distortion, volume
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.proc __sound
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sta tmp2 ;save volume
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jsr popa ;get distortion
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sta tmp1 ;save distortion
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jsr popa ;get pitch
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pha ;save in stack
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jsr popa ;get voice
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asl a ;adjust voice *2 for offset in x
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tax
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pla ;get pitch from stack
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sta AUDF1,x ;store pitch
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lda #0
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sta AUDCTL
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lda #3
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sta SKCTL ;init sound
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lda tmp1 ;get distortion
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asl a ;ignore the high nibble
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asl a
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asl a
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asl a
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clc ;setup for adding volume
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adc tmp2 ;add volume
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sta AUDC1,x ;volume + distortion in control channel
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rts
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.endproc
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