mirror of
https://github.com/cheat-engine/cheat-engine
synced 2026-08-15 02:26:08 -04:00
357 lines
5.3 KiB
NASM
Executable file
357 lines
5.3 KiB
NASM
Executable file
;16-bit bootsector
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;this will load the bigger loader to address 3000:0000
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;
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BITS 16
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GLOBAL main
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;SECTION .text
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main:
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jmp short loader ;0-1
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nop ;2
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OEMName: db 'CETC2.1' ;3-9
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dw 0 ;a-b (set by make)
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dw 0 ;c-d (set by make)
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bootdrive: db 0 ;e (set during boot)
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bootdrive2: db 0 ;f (set by installer)
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userdefinedbootdrive: db 0; 10 (set by installer, when set to 1 bootdrive2 is used instead of bootdrive+1 or if from floppy/cd 0x80)
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runwithoutmenu: db 0; 11 (set by installer, when set to 1 the menu will be skipped)
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db 0 ;12
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dw 0x00 ;13-14
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db 0; 0xf8 15
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dw 0x0000 ;16-17
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SPT: dw 62 ;18-19 for some reason my system won'y boot up with these missing so:
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NOH: dw 65 ;1a-1b
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;----------------------
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SectorsPerTrack: dw 0
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NumberOfHeads: dw 0
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NumberOfCylinders: dw 0
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currenttracksector: dw 0x2
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currenthead: dw 0
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;main:
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;jmp short after ;0-1
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;nop ;2
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;
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;name: db "CETC2.1" ;3-9
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;db 0
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;
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;BytesPerSector: dw 0; 512
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;SectorsPerCluster: db 0 ;8
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;
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;ReservedSectors: dw 0; 0x20 , 0x00
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;FatCopies: db 0; 0x02
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;RootDirEntries: dw 0x00
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;NumSectors: dw 0x00
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;MediaType: db 0; 0xf8
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;SectorsPerFAT: dw 0x0000
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;SectorsPerTrack: dw 62
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;NumberOfHeads: dw 65 ;, 0x00 , 0x00 , 0x00 , 0x00
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loader:
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;push 0
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;push 0x7c00
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;db 0x66,0x66,0xc3
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mov [0x7000],eax
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mov [0x7004],ebx
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mov [0x7008],ecx
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mov [0x700c],edx
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mov [0x7010],esi
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mov [0x7014],edi
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mov [0x7018],ebp
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mov [0x701c],esp
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mov ax,ss
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mov [0x7022],ax
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mov ax,ds
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mov [0x7024],ax
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mov ax,es
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mov [0x7026],ax
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mov ax,fs
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mov [0x7028],ax
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mov ax,gs
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mov [0x702a],ax
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pushf
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pop ax
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mov [0x702c],ax
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cli
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sgdt [0x7030]
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mov eax,cr0
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mov [start_CR0],eax
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;setup gs segment
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mov ax,0xb800
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mov gs,ax
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;basic initialization
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mov ax,3000h
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mov es,ax ;destination to 0x3000
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mov ax,cs
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mov ds,ax ;make sure data segment points to here
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mov [bootdrive],dl ;store the bootdrive register in ds:[bootdrive] (so local segment)
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xor ax,ax
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mov ss,ax ;might as well setup a place for the stack (0:7bf0)
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mov sp,0x3ff0
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call zeroUsableMemory
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call clearscreen
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mov si,msg
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call writeline
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sti
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push es
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push ds
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;reset disk
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mov ax,0
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int 13h
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;get disk info
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push es ;old version of bochs bypass
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mov ax,0x6000
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mov es,ax
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mov di,0
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mov ax,0800h
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int 13h
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pop es ;older version of bochs bug bypass (too lazy to recompile)
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inc dh
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mov [NumberOfHeads],dh
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mov ax,cx
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and ax,3fh
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inc ax
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mov [SectorsPerTrack],ax
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shr cx,6
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inc cx
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mov [NumberOfCylinders],cx
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mov cx,(size/512)+1 ; number of sectors to read
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mov bx,0x0000 ;offset to store at
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;now read the vmloader program from the disk to 3000:0000+)
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push cx
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reader:
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mov dword [es:bx],"FUCK"
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mov ax,0x0201 ;read 1 sector
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mov cx,[currenttracksector] ;track/sector
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mov dh,[currenthead]
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mov dl,[bootdrive] ; set dl to the bootdrive
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int 13h
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jc reader
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cmp dword [es:bx],"FUCK"
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je reader
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;successfull read, adjust parameters for next sector
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add bx,512 ;place to store at
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cmp bx,0
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jne checksector
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;overflow, vmloader has become bigger than 64KB, we need a new segment (0x40000?)
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mov bx,es
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add bx,0x1000 ;to the next free segment, 0x3000->0x4000->0x5000
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mov es,bx
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xor bx,bx
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checksector:
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;sector
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mov dx,[currenttracksector]
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inc dl
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mov [currenttracksector],dx
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push bx
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mov bl,'.'
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call writechar
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pop bx
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cmp dl,[SectorsPerTrack]
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jb adjusted_currentsector
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mov dl,1
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mov [currenttracksector],dx
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;head
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inc byte [currenthead]
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mov dl,[currenthead]
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cmp dl,[NumberOfHeads]
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jne adjusted_head
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mov byte [currenthead],0
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;cylinder
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inc dh
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mov [currenthead],dx
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adjusted_head:
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adjusted_currentsector:
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;check if done
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pop cx
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dec cx
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cmp cx,0
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push cx
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jne reader
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pop cx
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pop ds
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pop es
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done:
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mov dl,[bootdrive] ;just to be sure
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mov dword [0x7c00],0 ;location of lock (0=free)
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inc byte [currentline]
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;done
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jmp 3000h:0000h ;0x30000
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currentline: db 0
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currentcolumn: dw 0
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writechar:
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push ax
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mov al,80
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mul byte [currentline] ;ax = al*currentline (80*currentline)
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add ax,[currentcolumn]
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shl ax,1 ;multiply ax with 2
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xchg ax,di
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;ax=currentcolumn*currentline*2
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mov byte [gs:di],bl
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mov byte [gs:di+1],12
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xchg ax,di
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pop ax
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inc word [currentcolumn]
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ret
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writeline:
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mov ah,160
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mov al,[currentline]
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mul ah
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mov di,ax
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writeline_loop:
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cmp byte [si],0
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je writeline_done
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mov al,[si]
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mov [gs:di],al
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mov byte [gs:di+1],15
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add di,2
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inc si
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jmp writeline_loop
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writeline_done:
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inc byte [currentline]
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ret
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clearscreen:
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push es
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push gs
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pop es
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push cx
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mov cx,2*80*25 / 4
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rep stosd
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pop cx
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pop es
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ret
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zeroUsableMemory:
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push es
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pusha
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xor ax,ax
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int 0x12 ;get low memory size in KB
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test ax,ax
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je zeroUsabeMemory_error
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cmp ax,0x86
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je zeroUsabeMemory_error
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cmp ax,0x80
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je zeroUsabeMemory_error
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jmp zeroUsabeMemory_start
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zeroUsabeMemory_error:
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mov ax,600
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zeroUsabeMemory_start:
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sub ax,64 ;take out 64KB as a safeguard
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xchg bx,ax
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xor eax,eax
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mov si,0x1000
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zeroUsableMemory_clear:
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mov es,si
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mov cx,(0x1000/4)
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xor di,di
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rep stosd
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add si,0x1000
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sub bx,64
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jnb zeroUsableMemory_clear
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popa
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pop es
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ret
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msg:
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db 'DBVM BS',0
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times 506-($-$$) db 0 ; Pad to 509 bytes
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start_CR0:
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dd 0 ; storage location of original CR0
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BootSignature:
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dw 0aa55h ; BootSector signature ; 512 bytes
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