Assembly Source series of Getsect

This is the past DOS era of the compilation of source code, although has passed, but for the study of the assembly is still helpful, assembly language is just a basic programmer language, most people can grasp, not necessarily in-depth research.

; Absolute Disk read:getsec (uses BIOS interrupt 0x25)
;
; Interfaces to Computer innovations C-86 "C" Compiler V1.32 (& later)
; The DOS 2.10 Technical Reference page 5-10, and technical Reference
;　Page A-32. This code is written by Mike Sirmans (05-25-84).
; --------------------------------------------------------------------
; This routine is powerful. (And as SUCH, is dangerous in the wrong
;　Hands).　Being careful how to 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 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, &.
;
; Returns:null If the operation is successful.
; Otherwise, error codes are as follows:
;
; Hex attachment failed to respond.
; Hex Seek operation failed.
; Hex Controller failure.
; Hex Bad CRC on diskette read.
; Hex the DMA overrun on operation.
; Hex requested sector not found.
; Hex Write attempt on write-protected diskette.
; Hex address mark not found.
; Hex FF Unspecified (Error other than those above).
;
code segment byte public; segment registers remain intact
Assume Cs:code all the other registers would be destroyed
Public getsec
Getsec:push BP; save Old frame pointer
mov bp,sp; get new frame pointer
MOV AX,4[BP];p ut drive number into AL
XOR Ah,ah
MOV cx,6[bp]; Number of sectors to fetch
MOV DX,8[BP]; logical record number of 1st sector
mov bx,10[bp];p ointer 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;d etect 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 to AL only
Popf Remove Flags int 0x25 left on stack
Pop bp; restore original frame pointer
a ret;
Code ends
End