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59 lines
1.2 KiB
ArmAsm
59 lines
1.2 KiB
ArmAsm
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; Karri Kaksonen, 2010
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;
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; This function is used to place the Lynx hardware to point to any byte in
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; the Lynx cart.
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;
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; This function supports all available block sizes (512, 1024 and 2048 bytes).
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; No other block sizes have been used afaik.
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;
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; Only SEEK_SET operation mode is implemented.
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;
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; off_t __fastcall__ lseek(int fd, off_t offset, int whence);
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.importzp sp, sreg, regsave, regbank, tmp1, ptr1, ptr2
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.macpack longbranch
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.export _lseek
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.import addysp, stax0sp, tosand0ax, pusheax, asreax2
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.import ldeaxysp, decsp2, pushax, incsp8
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.import tosandeax,decax1,tosdiveax,axlong,ldaxysp
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.import lynxskip0, lynxblock,tosasreax
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.import __BLOCKSIZE__
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.importzp _FileCurrBlock
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.segment "CODE"
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.proc _lseek: near
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.segment "CODE"
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jsr pushax
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ldy #$05
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jsr ldeaxysp
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jsr pusheax
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ldx #$00
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lda #<(__BLOCKSIZE__/1024 + 9)
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jsr tosasreax
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sta _FileCurrBlock
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jsr lynxblock
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ldy #$05
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jsr ldeaxysp
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jsr pusheax
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lda #<(__BLOCKSIZE__-1)
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ldx #>(__BLOCKSIZE__-1)
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jsr axlong
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jsr tosandeax
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eor #$FF
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pha
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txa
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eor #$FF
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tay
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plx
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jsr lynxskip0
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ldy #$05
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jsr ldeaxysp
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jmp incsp8
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.endproc
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