;//Patch for XMS-driver to prevent A20 shutdown
;//Note: You can't compile this source directly
;// to executable
.386c
CS_SEG segment byte use16
assume cs:CS_SEG
XMSDRVADDRESS dd ?
REALXMSSTUFF db 5 dup (?)
FAKEXMSSTUFF db 0EAh
dw offset FAKEHIMEM, ?
RMEM_GDT db 000h,000h,000h,000h,000h,000h,000h,000h
db 0FFh,0FFh,000h,000h,000h,092h,0CFh,0FFh
RMEM_48 db 6 dup (?)
getvect MACRO vect,var
mov ah,035h
mov al,vect
int 021h
mov word ptr var[2],es
mov word ptr var[0],bx
endm
;// AL=VECT, DS:DX-->INT
setvect MACRO vect,var1,var2,var3
mov ah,025h
mov al,vect
push ds
mov dx,var1
mov ds,dx
mov dx,var2 var3
int 021h
pop ds
endm
setFAKE MACRO
cli
mov es,word ptr XMSDRVADDRESS[2]
mov di,word ptr XMSDRVADDRESS[0]
mov si,offset FAKEXMSSTUFF
mov ecx,5
rep movs byte ptr [di],cs:[si]
sti
endm
setREAL MACRO
cli
mov es,word ptr XMSDRVADDRESS[2]
mov di,word ptr XMSDRVADDRESS[0]
mov si,offset REALXMSSTUFF
mov ecx,5
rep movs byte ptr [di],cs:[si]
sti
endm
XMScall MACRO func,data
mov dx,data
mov ah,func
call dword ptr XMSDRVADDRESS
endm
XMSinit proc near
mov ax,04300h
int 02Fh
cmp al,080h
jne XM@ERROR
mov ax,04310h
int 02Fh
mov word ptr XMSDRVADDRESS[0],bx
mov word ptr XMSDRVADDRESS[2],es
XMScall 0,0
cmp ah,2
jb XM@ERROR
clc
ret
XM@ERROR:
stc
ret
XMSinit endp
FAKEHIMEM proc far
cmp ah,04h
je A20PROTECT
cmp ah,06h
je A20PROTECT
push si di cx es
setREAL
pop es cx di si
call dword ptr XMSDRVADDRESS
push si di cx es
setFAKE
pop es cx di si
retf
A20PROTECT:
xor ax,ax
mov bl,094h
retf
FAKEHIMEM endp
REALMEMORYINIT proc near
call XMSinit
XMScall 05h,00h
push ds
mov word ptr FAKEXMSSTUFF[3],cs
mov ds,word ptr XMSDRVADDRESS[2]
mov si,word ptr XMSDRVADDRESS[0]
push cs
pop es
mov di,offset REALXMSSTUFF
mov cx,5
rep movsb
pop ds
setFAKE
ret
REALMEMORYINIT endp
REALMEMORYDEINIT proc near
setREAL
ret
REALMEMORYDEINIT endp
CS_SEG ends
end
