mirror of
https://github.com/reactos/reactos.git
synced 2024-12-28 10:04:49 +00:00
187 lines
4.5 KiB
ArmAsm
187 lines
4.5 KiB
ArmAsm
/*
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* COPYRIGHT: See COPYING in the top level directory
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* PROJECT: ReactOS Bootsector for ISO file system
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* PURPOSE: Normal DOS boot sector
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* Ported to NASM from FreeDOS fdisk 1.2.0 by:
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* PROGRAMMERS: Casper Hornstrup (chorns@users.sourceforge.net)
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*/
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/* INCLUDES ******************************************************************/
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#include <asm.inc>
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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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.code16
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real_start:
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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, HEX(7c00)
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lea sp, [bp-32]
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sti
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/* Copy 512 bytes of MBR to 1fe0:7c00 */
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mov ax, HEX(1FE0)
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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, 256
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rep movsw
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/* Jump into relocated code */
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ljmp16 HEX(1FE0), cont
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cont:
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/* Setup segment registers */
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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 + HEX(1be)] // start of partition table
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test_next_for_active:
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test byte ptr ds:[di], HEX(80)
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jne active_partition_found
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add di, 16 // next table
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cmp di, HEX(07c00) + HEX(1fe) // 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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.asciz "No active partition found"
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WAIT_FOR_REBOOT:
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jmp WAIT_FOR_REBOOT
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/*****************************************************************/
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trouble_reading_drive:
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call print
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.asciz "Read error while reading drive"
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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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.asciz "Partition signature != 55AA"
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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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// .asciz "Loading active partition"
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call read_boot_sector
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jc trouble_reading_drive
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cmp word ptr es:[HEX(7c00)+HEX(1fe)], HEX(0aa55)
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jne invalid_partition_code
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ljmp16 0, HEX(7c00) // 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, HEX(55aa)
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mov ah, HEX(41)
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int HEX(13)
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jc StandardBios // if (regs.b.x != 0xaa55 || (regs.flags & 0x01))
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cmp bx, HEX(0aa55) // 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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.byte 16
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.byte 0
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.byte 4 // read four sectors - why not
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.byte 0
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.word HEX(7c00) // fixed boot address for DOS sector
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.word HEX(0000)
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_bios_LBA_low:
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.word 0
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_bios_LBA_high:
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.word 0
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.word 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 word ptr ds:[_bios_LBA_low], ax
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mov ax,[di + 8 + 2]
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mov word ptr ds:[_bios_LBA_high], ax
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mov ax, HEX(4200) // regs.a.x = LBA_READ;
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mov si, offset _bios_LBA_address_packet // regs.si = FP_OFF(&dap);
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int HEX(13)
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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, HEX(0204) // regs.a.x = 0x0201;
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mov bx, HEX(7c00) // regs.b.x = FP_OFF(buffer);
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/* 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 cx, word ptr ds:[di + 2]
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mov dh, byte ptr ds:[di + 1] // regs.d.b.h = chs.Head;
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// regs.es = FP_SEG(buffer);
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int HEX(13)
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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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*/
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print_1char:
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xor bx, bx // video page 0
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mov ah, HEX(0E) // else print it
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int HEX(10) // via TTY mode
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print:
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pop si // this is the first character
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print1:
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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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.org 510
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.byte HEX(55), HEX(0aa)
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.endcode16
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END
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