mirror of
https://github.com/reactos/reactos.git
synced 2024-10-30 19:41:57 +00:00
180 lines
4.8 KiB
NASM
180 lines
4.8 KiB
NASM
;
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; normal DOS boot sector
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;
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; Ported to nasm from FreeDOS fdisk 1.2.0 by:
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; Casper Hornstrup (chorns@users.sourceforge.net)
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;
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align 2, db 0
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global _bootnormal_code
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_bootnormal_code:
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;-----------------------------------------------------------------------
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; ENTRY (copied from freedos bootsector)
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;
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; IN: DL = boot drive
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;OUT: DL = boot drive
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;
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;-----------------------------------------------------------------------
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real_start: cli
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cld
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xor ax, ax
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mov ss, ax ; initialize stack
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mov ds, ax
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mov bp, 0x7c00
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lea sp, [bp-0x20]
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sti
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mov ax, 0x1FE0
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mov es, ax
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mov si, bp
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mov di, bp
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mov cx, 0x0100
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rep movsw
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jmp word 0x1FE0:0x7c00+ cont-real_start
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cont: mov ds, ax
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mov ss, ax
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xor ax,ax
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mov es,ax
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; search for active partition
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lea di, [bp+0x1be] ; start of partition table
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test_next_for_active:
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test byte [di],0x80
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jne active_partition_found
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add di,0x10 ; next table
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cmp di, 07c00h+0x1fe; scanned beyond end of table ??
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jb test_next_for_active
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;*****************************************************************
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call print
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db 'no active partition found',0
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WAIT_FOR_REBOOT:
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jmp $
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;*****************************************************************
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trouble_reading_drive:
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call print
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db 'read error while reading drive',0
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jmp WAIT_FOR_REBOOT
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;*****************************************************************
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invalid_partition_code:
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call print
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db 'partition signature != 55AA',0
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jmp WAIT_FOR_REBOOT
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;*****************************************************************
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active_partition_found:
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; call print
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; db 'loading active partition',0
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call read_boot_sector
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jc trouble_reading_drive
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cmp word [es:0x7c00+0x1fe],0xaa55
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jne invalid_partition_code
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jmp word 0x0:0x7c00 ; and jump to boot sector code
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;*****************************
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; read_boot_sector
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;
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; IN: DI--> partition info
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;OUT:CARRY
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;*****************************
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read_boot_sector:
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; /* check for LBA support */
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mov bx,0x55aa
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mov ah,0x41
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int 0x13
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jc StandardBios ; if (regs.b.x != 0xaa55 || (regs.flags & 0x01))
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cmp bx,0xaa55 ; goto StandardBios;
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jne StandardBios
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; /* if DAP cannot be used, don't use LBA */
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; if ((regs.c.x & 1) == 0)
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; goto StandardBios;
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test cl,1
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jz StandardBios
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jmp short LBABios
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_bios_LBA_address_packet:
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db 0x10
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db 0
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db 4 ; read four sectors - why not
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db 0
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dw 0x7c00 ; fixed boot address for DOS sector
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dw 0x0000
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_bios_LBA_low dw 0
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_bios_LBA_high dw 0
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dw 0,0
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LBABios:
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; copy start address of partition to DAP
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mov ax,[di+8]
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mov [0x7c00+ (_bios_LBA_low-real_start)],ax
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mov ax,[di+8+2]
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mov [0x7c00+ (_bios_LBA_high-real_start)],ax
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mov ax,0x4200 ; regs.a.x = LBA_READ;
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mov si,0x7c00+ (_bios_LBA_address_packet-real_start); regs.si = FP_OFF(&dap);
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int 0x13
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ret
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;*****************************************************************
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; read disk, using standard BIOS
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;
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StandardBios:
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mov ax,0x0204 ; regs.a.x = 0x0201;
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mov bx,0x7c00 ; regs.b.x = FP_OFF(buffer);
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mov cx,[di+2] ; regs.c.x =
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; ((chs.Cylinder & 0xff) << 8) + ((chs.Cylinder & 0x300) >> 2) +
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; chs.Sector;
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; that was easy ;-)
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mov dh,[di+1] ; regs.d.b.h = chs.Head;
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; regs.es = FP_SEG(buffer);
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int 0x13
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ret
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;****** PRINT
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; prints text after call to this function.
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print_1char:
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xor bx, bx ; video page 0
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mov ah, 0x0E ; else print it
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int 0x10 ; via TTY mode
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print: pop si ; this is the first character
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print1: lodsb ; get token
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push si ; stack up potential return address
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cmp al, 0 ; end of string?
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jne print_1char ; until done
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ret ; and jump to it
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times 0x1fe-$+$$ db 0
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db 0x55,0xaa
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