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|
; -*- fundamental -*- (asm-mode sucks)
; $Id$
; ****************************************************************************
;
; memdisk.asm
;
; A program to emulate an INT 13h disk BIOS from a "disk" in extended
; memory.
;
; Copyright (C) 2001 H. Peter Anvin
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
; USA; either version 2 of the License, or (at your option) any later
; version; incorporated herein by reference.
;
; ****************************************************************************
org 0h
MyStack equ 1024
; Parameter registers definition; this is the definition
; of the stack frame.
%define P_EAX dword [bp+28]
%define P_AX word [bp+28]
%define P_AL byte [bp+28]
%define P_AH byte [bp+29]
%define P_ECX dword [bp+24]
%define P_CX word [bp+24]
%define P_CL byte [bp+24]
%define P_CH byte [bp+25]
%define P_EDX dword [bp+20]
%define P_DX word [bp+20]
%define P_DL byte [bp+20]
%define P_DH byte [bp+21]
%define P_EBX dword [bp+16]
%define P_BX word [bp+16]
%define P_BL byte [bp+16]
%define P_BH byte [bp+17]
%define P_EBP dword [bp+8]
%define P_BP word [bp+8]
%define P_ESI dword [bp+4]
%define P_SI word [bp+4]
%define P_EDI dword [bp]
%define P_DI word [bp]
section .text
Int13Start:
; See if DL points to our class of device (FD, HD)
push dx
xor dl,[cs:DriveNo]
pop dx
js .nomatch ; If SF=0, we have a match here
cmp dl,[cs:DriveNo]
je .our_drive
jb .nomatch ; Drive < Our drive
dec dl ; Drive > Our drive, adjust drive #
.nomatch:
jmp far [OldInt13]
.our_drive:
mov [cs:Stack],sp
mov [cs:SavedAX],ax
mov ax,ss
mov [cs:Stack+2],ax
mov ax,cs
mov ss,ax
mov sp,MyStack
push ds
push es
mov ds,ax
mov es,ax
mov ax,[SavedAX]
pushad
mov bp,sp
cmp ah,Int13FuncsMax
jae Invalid
xor al,al ; AL = 0 is standard entry condition
mov di,ax
shr di,7
call [Int13Funcs+di]
Done: ; Standard routine for return
mov [LastStatus],ah
mov P_AX,ax
cmp ah,1
setnb al ; AL <- (AH > 0) ? 1 : 0 (CF)
lds bx,[Stack] ; DS:BX <- Old stack pointer
mov [bx+4],al ; Low byte of old FLAGS -> arithmetric flags
popad
pop es
pop ds
lss sp,[cs:Stack]
iret
Reset:
; Reset affects multiple drives, so we need to pass it on
pop ax ; Drop return address
mov [LastStatus], byte 0
popad
pop es
pop ds
lss sp,[cs:Stack]
and dl,80h ; Clear all but the type bit
jmp far [OldInt13]
GetStatus:
mov ah,[LastStatus] ; Copy last status
ret
CheckIfReady:
Recalibrate:
xor ah,ah ; Always successful
ret
Read:
Write:
Verify:
Format:
GetParms:
InitWithParms:
Seek:
GetDriveType:
DetectChange:
Invalid:
mov ah,01h ; Unsupported function
ret
section .data
Int13Funcs dw Reset ; 00h - RESET
dw GetStatus ; 01h - GET STATUS
dw Read ; 02h - READ
dw Write ; 03h - WRITE
dw Verify ; 04h - VERIFY
dw Format ; 05h - FORMAT TRACK
dw Format ; 06h - FORMAT TRACK AND SET BAD FLAGS
dw Format ; 07h - FORMAT DRIVE AT TRACK
dw GetParms ; 08h - GET PARAMETERS
dw InitWithParms ; 09h - INITIALIZE CONTROLLER WITH DRIVE PARAMETERS
dw Invalid ; 0Ah
dw Invalid ; 0Bh
dw Seek ; 0Ch - SEEK TO CYLINDER
dw Reset ; 0Dh - RESET HARD DISKS
dw Invalid ; 0Eh
dw Invalid ; 0Fh
dw CheckIfReady ; 10h - CHECK IF READY
dw Recalibrate ; 11h - RECALIBRATE
dw Invalid ; 12h
dw Invalid ; 13h
dw Invalid ; 14h
dw GetDriveType ; 15h - GET DRIVE TYPE
dw DetectChange ; 16h - DETECT DRIVE CHANGE
Int13FuncsEnd equ $
Int13FuncsMax equ (Int13FuncsEnd-Int13Funcs) >> 1
DriveNo db 0 ; Our drive number
LastStatus db 0 ; Last return status
section .bss
OldInt13 resd 1 ; INT 13h in chain
Stack resd 1 ; Saved SS:SP on invocation
SavedAX resw 1 ; AX saved during initialization
|
