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segment loader use16
init:
mov ax,1687h
int 2Fh
or ax,ax ; DPMI installed?
jnz short no_dpmi
test bl,1 ; 32-bit programs supported?
jz short no_dpmi
mov word [cs:mode_switch],di
mov word [cs:mode_switch+2],es
mov bx,si ; allocate memory for DPMI data
mov ah,48h
int 21h
jnc init_protected_mode
init_failed:
call init_error
db 'error: DPMI initialization failed.',0Dh,0Ah,0
no_dpmi:
call init_error
db 'error: 32-bit DPMI services are not available.',0Dh,0Ah,0
init_error:
pop si
push cs
pop ds
display_error:
lodsb
test al,al
jz short error_finish
mov dl,al
mov ah,2
int 21h
jmp short display_error
error_finish:
mov ax,4CFFh
int 21h
init_protected_mode:
mov es,ax
mov ds,[ds:2Ch]
mov ax,1
call far [cs:mode_switch] ; switch to protected mode
jc init_failed
mov cx,1
xor ax,ax
int 31h ; allocate descriptor for code
jc init_failed
mov si,ax
xor ax,ax
int 31h ; allocate descriptor for data
jc init_failed
mov di,ax
mov dx,cs
lar cx,dx
shr cx,8
or cx,0C000h
mov bx,si
mov ax,9
int 31h ; set code descriptor access rights
jc init_failed
mov dx,ds
lar cx,dx
shr cx,8
or cx,0C000h
mov bx,di
int 31h ; set data descriptor access rights
jc init_failed
mov ecx,main
shl ecx,4
mov dx,cx
shr ecx,16
mov ax,7
int 31h ; set data descriptor base address
jc init_failed
mov bx,si
int 31h ; set code descriptor base address
jc init_failed
mov cx,0FFFFh
mov dx,0FFFFh
mov ax,8 ; set segment limit to 4 GB
int 31h
jc init_failed
mov bx,di
int 31h
jc init_failed
mov ax,ds
mov ds,di
mov [psp_selector],es
mov [environment_selector],ax
cli
mov ss,di
mov esp,stack_top
sti
mov es,di
xor eax,eax
mov [memory_handles_count],eax
push si
push start
retf
mode_switch dd ?
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