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Filename : ABSDISK.ASM

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;
; ABSDISK.ASM
;
; Originally published as part of The MicroFirm Function Library
; This version released to the public domain by the author, Bob Stout
;
; Requires MASM 5.1 or later or equivalent
;
; Assemble with: MASM /Mx /z ...
; TASM /jMASM /mx /z ...
;

% .MODEL memodel,C ;Add model support via
;command line macro,
;e.g. MASM /Dmemodel=LARGE ...
extrn _osmajor:BYTE
public absdisk

.DATA
start dw ?
fill dw 0
number dw ?
buf dw ?,?

.CODE
absdisk PROC USES SI DI BP, func:BYTE, drive:WORD, num_sec:WORD, start_sec:WORD, buffer:PTR
mov AX,drive ;Get drive number in AL
mov AH,_osmajor ;Load OS version in AH
mov CX,num_sec ;Set up regs for DOS 3 call
mov DX,start_sec
IF @DataSize
push DS ;Save DS in L & C models
lds BX,buffer
ELSE
mov BX,buffer
ENDIF
cmp AH,4 ;DOS 4+?
jb doint ;No, skip it
mov start,DX ;Yes, fill in DCB structure
mov number,CX
mov buf,BX
mov buf+2,DS
mov cx,-1
IF @DataSize ;Point to DCB
mov BX,@Data
mov DS,BX
ENDIF
mov bx,OFFSET start
doint: mov AH,func ;Read or Write?
cmp AH,25h
jne skip_1
int 25h ;Read sector
jmp skip_3
skip_1: cmp AH,26h
jne skip_2
int 26h ;Write sector
jmp skip_3
skip_2: stc ;Invalid command
mov AX,-1
skip_3: jc bye ;Error?
mov AX,0 ;No, return SUCCESS
bye: add SP,2 ;Int 25h leave the flags on the stack
IF @DataSize
pop DS ;Restore DS in L & C models
ENDIF
ret

absdisk ENDP

end