汇编源码--getsect

;	Absolute Disk Read:  GETSEC  ( uses BIOS interrupt 0x25 )
;
;	Interfaces to Computer Innovations C-86 "c" compiler V1.32 (& later)
;	See DOS 2.10 Technical Reference page 5-10, and Technical Reference
;	page A-32.  This code was written by Mike Sirmans (05-25-84).
;	--------------------------------------------------------------------
;       THIS ROUTINE IS POWERFUL. (AND AS SUCH, IS DANGEROUS IN THE WRONG
;       HANDS).  BE CAREFUL HOW YOU USE IT.  I ASSUME NO RESPONSIBILITY.
;	--------------------------------------------------------------------
;
;	Synopsis:	int getsec(drive,numsec,begsec,buffer)
;			unsigned int drive;	/* 0=A, 1=B, etc. */
;			unsigned int numsec;	/* Number of sectors to read */
;			unsigned int begsec;	/* Beginning logical sector */
;			char *buffer;		/* Transfer address */
;
;	Function:	The number of sectors specified are transferred 
;			between	the given drive and the transfer address. 
;			LOGICAL SECTOR NUMBERS are obtained by numbering
;			each sector sequentially starting from track 0, head 0,
;			sector 1 (logical sector 0) and continuing along the
;			same head, then to the next head until the last sector
;			on the last head of the track is counted.  Thus, 
;			logical sector 1 is track 0, head 0, sector 2,
;			logical sector 2 is track 0, head 0, sector 3,  & so on.
;
;	Returns:	NULL if the operation is successful.
;			otherwise, error codes are as follows:
;
;			hex 80	Attachment failed to respond.
;			hex 40	SEEK operation failed.
;			hex 20	Controller failure.
;			hex 10  Bad CRC on diskette read.
;			hex 08	DMA overrun on operation.
;			hex 04	Requested sector not found.
;			hex 03	Write attempt on write-protected diskette.
;			hex 02	Address mark not found.
;			hex FF	Unspecified (error other than those above).
;
code	segment	byte public		;segment registers remain intact
	assume	cs:code			;all other registers will be destroyed
	public	getsec

getsec: push	bp			;save old frame pointer
	mov	bp,sp			;get new frame pointer
	mov	ax,4		;put drive number into AL
	xor	ah,ah
	mov	cx,6		;number of sectors to fetch
	mov	dx,8		;logical record number of 1st sector
	mov     bx,10		;pointer to transfer address
	int	25h			;BIOS call
	jc	error			;error has occurred if carry flag = 1
	mov	al,00H			;NULL to indicate sucessful completion
	jmp	done
error:	cmp	al,00H			;detect unspecified error code 00H
	jne	done			;...change to 0FFh if found to 
	mov	al,0FFH			;...differentiate it from success code
done:	xor	ah,ah			;return AL only
	popf				;remove flags int 0x25 left on stack
	pop	bp			;restore original frame pointer
	ret				;all done

code	ends
	end