435 lines
9.6 KiB
NASM
435 lines
9.6 KiB
NASM
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;++
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;
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;Copyright (c) 1995 Microsoft Corporation
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;
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;Module Name:
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;
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; bioschk.asm
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;
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;Abstract:
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;
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; The code in this "image" is responsible for checking if is appropriate
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; for us to start setupldr.bin. We consider this appropriate when we pass
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; BIOS checkings. Setupldr.bin is binary appended at the end of this image.
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;
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;Author:
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;
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; Calin Negreanu (calinn) 16-Dec-1999
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;
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;Environment:
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;
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; Real mode
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; Case 1:
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; Complete image has been loaded at 2000:0000 by the boot code
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; DL = meaningfull data
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; Case 2:
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; First 512 bytes of this image has been loaded at 2000:000 by the boot code
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; BX = meaningfull data
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; DL = meaningfull data
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; DS:SI -> points to a structure containing meaningfull data
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; DS:DI -> points to a structure containing meaningfull data
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;
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;Revision History:
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;
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;--
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page ,132
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title boot - BIOS check
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name bioschk
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.8086
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CODE SEGMENT
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ASSUME CS:CODE,DS:CODE,SS:NOTHING,ES:NOTHING
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ORG 0000H
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_BiosChk label byte
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BiosChkDestSeg EQU 1000h
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SetupLdrDestSeg EQU 2000h
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MaxCodeSize EQU 0800h ;number of paragraphs (32k)
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MaxSetupLdrSize EQU 4000h ;number of paragraphs (256k)
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StackSeg EQU 1000h ;stack goes from here
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MAXREAD EQU 10000h
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MAXSECTORS EQU MAXREAD/0200h
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DoubleWord struc
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lsw dw ?
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msw dw ?
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DoubleWord ends
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SHARED struc
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ReadClusters dd ?
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ReadSectors dd ?
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SectorBase dd ?
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SHARED ends
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BPB struc
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BytesPerSector dw ?
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SectorsPerCluster db ?
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ReservedSectors dw ?
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Fats db ?
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DirectoryEntries dw ?
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Sectors dw ?
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Media db ?
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FatSectors dw ?
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SectorsPerTrack dw ?
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Heads dw ?
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HiddenSectors dd ?
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SectorsLong dd ?
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BootDriveNumber db ?
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BPB ends
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JMPFAR MACRO DestOfs,DestSeg
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db 0eah
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dw OFFSET DestOfs
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dw DestSeg
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endm
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START:
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; If we boot from FAT drives, the next instruction is not executed.
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jmp RealStart
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FatBegin:
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.386
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;
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; If we're here, we've booted off a FAT system and we must load the rest
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; of the binary image at 2000:0200 (right behind this sector).
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;
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;
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; Save away meaningfull data
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;
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push dx
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push bx
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.386
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push 06000h
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.8086
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pop es
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xor bx,bx
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mov cx,ds:[si].ReservedSectors
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mov ds:[di].SectorBase.msw,0
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mov ds:[di].SectorBase.lsw,cx
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mov ax,ds:[si].FatSectors
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cmp ax,080h
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jbe FatLt64k
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push cx
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mov ax,080h
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call ds:[di].ReadSectors
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pop cx
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.386
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push 07000h
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.8086
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pop es
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xor bx,bx
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mov ax,ds:[si].FatSectors
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sub ax,080h
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add cx,080h
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mov ds:[di].SectorBase.lsw,cx
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adc ds:[di].SectorBase.msw,0
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FatLt64k:
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call ds:[di].ReadSectors
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pop dx
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xor bx,bx
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.386
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mov ax,6000h
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mov fs,ax
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mov ax,7000h
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mov gs,ax
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.8086
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push cs
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pop es
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mov ah,MAXSECTORS
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FatLoop:
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push dx
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mov al,ds:[si].SectorsPerCluster
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sub ah,ds:[si].SectorsPerCluster
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cmp dx,0ffffh
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jne Fat10
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pop dx
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pop dx
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jmp RealStart
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Fat10:
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mov cx,dx
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call NextFatEntry
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inc cx
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cmp dx,cx
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jne LncLoad
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cmp ah,0
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jne Lnc20
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mov ah,MAXSECTORS
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jmp short LncLoad
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Lnc20:
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add al,ds:[si].SectorsPerCluster
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sub ah,ds:[si].SectorsPerCluster
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jmp short Fat10
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LncLoad:
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pop cx
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push dx
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mov dx,cx
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mov cx,10
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FatRetry:
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push bx
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push ax
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push dx
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push cx
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call [di].ReadClusters
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jnc ReadOk
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mov ax,01h
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mov al,ds:[si].BootDriveNumber
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int 13h
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xor ax,ax
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mov al,ds:[si].BootDriveNumber
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int 13h
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xor ax,ax
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FatPause:
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dec ax
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jnz FatPause
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pop cx
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pop dx
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pop ax
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pop bx
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dec cx
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jnz FatRetry
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push cs
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pop ds
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mov si,offset FAT_ERROR
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FatErrPrint:
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lodsb
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or al,al
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jz FatErrDone
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mov ah,14
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mov bx,7
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int 10h
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jmp FatErrPrint
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FatErrDone:
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jmp $
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FAT_ERROR db 13,10,"Disk I/O error",0dh,0ah,0
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ReadOk:
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pop cx
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pop dx
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pop ax
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pop bx
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pop dx
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.386
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mov cl,al
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xor ch,ch
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shl cx,9
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.8086
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add bx,cx
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jz FatLoopDone
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jmp FatLoop
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FatLoopDone:
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mov ax,es
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add ax,01000h
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mov es,ax
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mov ah,MAXSECTORS
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jmp FatLoop
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NextFatEntry proc near
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push bx
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call IsFat12
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jnc Next16Fat
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Next12Fat:
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mov bx,dx
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shr dx,1
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pushf
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add bx,dx
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.386
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mov dx,fs:[bx]
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.8086
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popf
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jc shift
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and dx,0fffh
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jmp short N12Tail
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shift:
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.386
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shr dx,4
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.8086
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N12Tail:
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cmp dx,0ff8h
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jb NfeDone
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mov dx,0ffffh
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jmp short NfeDone
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Next16Fat:
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add dx,dx
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jc N16high
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mov bx,dx
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.386
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mov dx,fs:[bx]
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.8086
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jmp short N16Tail
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N16high:
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mov bx,dx
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.386
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mov dx,gs:[bx]
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.8086
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N16Tail:
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cmp dx,0fff8h
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jb NfeDone
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mov dx,0ffffh
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NfeDone:
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pop bx
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ret
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NextFatEntry endp
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IsFat12 proc near
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.386
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push eax
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push ebx
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push ecx
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push edx
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movzx ecx, ds:[si].Sectors
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or cx,cx
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jnz if10
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mov ecx, ds:[si].SectorsLong
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if10:
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movzx ebx, byte ptr ds:[si].Fats
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movzx eax, word ptr ds:[si].FatSectors
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mul ebx
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sub ecx,eax
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movzx eax, word ptr ds:[si].DirectoryEntries
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shl eax, 5
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mov edx,eax
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and edx,0ffff0000h
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div word ptr ds:[si].BytesPerSector
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sub ecx,eax
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movzx eax, word ptr ds:[si].ReservedSectors
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sub ecx, eax
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mov eax, ecx
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movzx ecx, byte ptr ds:[si].SectorsPerCluster
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xor edx,edx
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div ecx
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cmp eax, 4087
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jae if20
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stc
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jmp short if30
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if20:
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clc
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if30:
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pop edx
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pop ecx
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pop ebx
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pop eax
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ret
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.8086
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IsFat12 endp
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Free EQU 512-($-Start)
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if Free lt 0
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%out FATAL PROBLEM: FAT-specific startup code is greater than
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%out 512 bytes. Fix it!
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.err
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endif
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RealStart:
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;
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; we are completely done with the boot sector, we can party on it's memory as we like.
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; set up the stack
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;
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mov ax,StackSeg
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mov ss,ax
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xor sp,sp
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mov ax,cs
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mov ds,ax
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mov es,ax
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;
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; save setupldr data
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;
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mov Preserve, dl
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; move ourselves from 2000:0000 to 1000:0000, one paragraph at a time.
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mov ax, BiosChkDestSeg
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mov es, ax
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mov dx, MaxCodeSize
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cld
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Again1:
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xor di, di
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xor si, si
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mov cx, 10h
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rep movsb
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mov ax, ds
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inc ax
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mov ds, ax
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mov ax, es
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inc ax
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mov es, ax
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dec dx
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jnz Again1
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mov ax, BiosChkDestSeg
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mov ds, ax
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mov es, ax
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JMPFAR Continue1, BiosChkDestSeg
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Continue1:
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; insert your BIOS check code here
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; instead of a real BIOS check we will check if the user holds down CTRL.
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; If yes, we will behave like BIOS check failed
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mov ah,02h
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int 16h
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and al,00000100b
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jz MoveSetupLdr
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; at this point, the BIOS check failed. You can add whatever code you want here
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; to give a message or to make the computer crash. If you don't do anything, the
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; code will jump to 2000:0000 so an infinite loop is going to happen.
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jmp Continue2
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MoveSetupLdr:
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; move Setupldr code from 2000+MaxCodeSize:0000 to 2000:0000, one paragraph at a time.
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push ds
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push es
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mov ax, SetupLdrDestSeg
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mov es, ax
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add ax, MaxCodeSize
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mov ds, ax
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mov dx, MaxSetupLdrSize
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cld
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Again2:
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xor di, di
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xor si, si
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mov cx, 10h
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rep movsb
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mov ax, ds
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inc ax
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mov ds, ax
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mov ax, es
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inc ax
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mov es, ax
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dec dx
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jnz Again2
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pop es
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pop ds
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Continue2:
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mov dl, Preserve
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JMPFAR 0,SetupLdrDestSeg
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Preserve db ?
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.errnz ($-_BiosChk) GT (MaxCodeSize*16 - 2) ;FATAL: BiosChk code is too large
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org MaxCodeSize*16 - 2
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db 55h,0aah
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CODE ENDS
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END START
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