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42 lines
757 B
ArmAsm
42 lines
757 B
ArmAsm
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; Christian Groessler, May-2000
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; Moved from fdtable.s to it's own file by Daniel Serpell, 2009.
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;
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; Convert file descriptor to IOCB number
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;
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.include "atari.inc"
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.include "fd.inc"
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.import fd_table,fd_index
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.export fdtoiocb
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.code
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; gets fd in ax
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; return iocb index in A, fd_table index in X
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; return N bit set for invalid fd
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; all registers destroyed
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.proc fdtoiocb
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cpx #0
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bne inval
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cmp #MAX_FD_INDEX
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bcs inval
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tax
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lda fd_index,x
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asl a ; create index into fd table
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asl a
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tax
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lda #$ff
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cmp fd_table+ft_iocb,x ; entry in use?
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beq inval ; no, return error
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lda fd_table+ft_usa,x ; get usage counter
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beq inval ; 0? should not happen
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lda fd_table+ft_iocb,x ; get iocb
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rts
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inval: ldx #$ff ; sets N
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rts
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.endproc ; fdtoiocb
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