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