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94 lines
1.8 KiB
ArmAsm
94 lines
1.8 KiB
ArmAsm
;
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; 2012-10-16, Oliver Schmidt
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; 2014-07-16, Greg King
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;
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; unsigned char __fastcall__ _syschdir (const char* name);
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;
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.export __syschdir
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.import diskinit, fnunit, curunit, initcwd
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.importzp ptr1, tmp1, tmp2
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;--------------------------------------------------------------------------
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; __syschdir
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.proc __syschdir
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; Save name
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sta ptr1
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stx ptr1+1
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; Process first character
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ldy #0
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lda (ptr1),y
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beq err
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jsr getdigit
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bcs err
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tax
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; Process second character
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iny
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lda (ptr1),y
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beq init
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jsr getdigit
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bcs err
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stx tmp1 ; First digit
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sta tmp2 ; Second digit
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; Multiply first digit by 10
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txa
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asl a ; * 2
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asl a ; * 4, carry cleared
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adc tmp1 ; * 5
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asl a ; * 10, carry cleared
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; Add second digit to product
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adc tmp2
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tax
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; Process third character
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iny
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lda (ptr1),y
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bne err
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; Check device readiness
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init: txa
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jsr diskinit
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bne done
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; Success, update cwd
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lda fnunit ; Set by diskinit
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sta curunit
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jmp initcwd ; Returns with A = 0
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; Return with error in A
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err: lda #9 ; "Illegal device"
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done: rts
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.endproc
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;--------------------------------------------------------------------------
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; getdigit -- Converts PetSCII to binary.
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; Sets carry if the character is outside of '0'-'9'.
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.proc getdigit
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sec
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sbc #'0'
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bcs @L0
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sec
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rts
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@L0: cmp #10
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rts
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.endproc
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