55 lines
2.0 KiB
NASM
55 lines
2.0 KiB
NASM
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; Synopsis: int getsec(drive,numsec,begsec,buffer)
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; unsigned int drive; /* 0=A, 1=B, etc. */
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; unsigned int numsec; /* Number of sectors to read */
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; unsigned int begsec; /* Beginning logical sector */
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; char *buffer; /* Transfer address */
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;
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; Function: The number of sectors specified are transferred
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; between the given drive and the transfer address.
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; LOGICAL SECTOR NUMBERS are obtained by numbering
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; each sector sequentially starting from track 0, head 0,
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; sector 1 (logical sector 0) and continuing along the
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; same head, then to the next head until the last sector
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; on the last head of the track is counted. Thus,
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; logical sector 1 is track 0, head 0, sector 2,
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; logical sector 2 is track 0, head 0, sector 3, & so on.
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;
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; Returns: NULL if the operation is successful.
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; otherwise, error codes are as follows:
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;
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; hex 80 Attachment failed to respond.
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; hex 40 SEEK operation failed.
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; hex 20 Controller failure.
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; hex 10 Bad CRC on diskette read.
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; hex 08 DMA overrun on operation.
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; hex 04 Requested sector not found.
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; hex 03 Write attempt on write-protected diskette.
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; hex 02 Address mark not found.
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; hex FF Unspecified (error other than those above).
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;
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code segment byte public ;segment registers remain intact
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assume cs:code ;all other registers will be destroyed
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public getsec
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getsec: push bp ;save old frame pointer
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mov bp,sp ;get new frame pointer
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mov ax,4[bp] ;put drive number into AL
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xor ah,ah
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mov cx,6[bp] ;number of sectors to fetch
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mov dx,8[bp] ;logical record number of 1st sector
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mov bx,10[bp] ;pointer to transfer address
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int 25h ;BIOS call
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jc error ;error has occurred if carry flag = 1
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mov al,00H ;NULL to indicate sucessful completion
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jmp done
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error: cmp al,00H ;detect unspecified error code 00H
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jne done ;...change to 0FFh if found to
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mov al,0FFH ;...differentiate it from success code
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done: xor ah,ah ;return AL only
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popf ;remove flags int 0x25 left on stack
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pop bp ;restore original frame pointer
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ret ;all done
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code ends
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end
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