! mbr.S - a replacement master boot record
! Copyright (C) 1995,1999-2001 Neil Turton
! See the file AUTHORS for a list of contributors.
!
!    This program is free software; you can redistribute it and/or modify
!    it under the terms of the GNU General Public License as published by
!    the Free Software Foundation; either version 2 of the License, or
!    (at your option) any later version.
!
!    This program is distributed in the hope that it will be useful,
!    but WITHOUT ANY WARRANTY; without even the implied warranty of
!    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
!    GNU General Public License for more details.
!
!    You should have received a copy of the GNU General Public License
!    along with this program; if not, write to the Free Software
!    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

!!! High level feature selection.
	
#define LOGO

#ifdef Y2KBUG
#undef LOGO
#endif

#undef COMPAT
#define NEW_FORMAT

!!! Low level feature selection.

cfg_asm_flags:	set 0
#ifdef Y2KBUG
cfg_asm_flags:	set cfg_asm_flags | 1
#endif
#ifdef TESTDISK
cfg_asm_flags:	set cfg_asm_flags | 2
#endif	

! Setup the flags with cool settings. Have no delay, but allow
! interrupt. We mark everything bootable, but default to booting
! the active partition.
cfg_flags: set 0x90 ! Floppy bootable. Advanced mode available.

cfg_def:	set 0xc7 ! Boot active partition, Interrupt by anything.

! Delay in timer ticks. 0=>No delay. 65535=>Interrupt.
cfg_delay:	set 18  ! About a second.

cfg_drive:	set 0x80 ! /dev/hda

#ifdef TESTDISK
cfg_delay:	set 0
cfg_flags:	set 0x1f ! Boot anything.
#endif

#ifdef COMPAT
! Setup the flags to mimic standard MBRs unless interrupted
! flags:bits 0-4 marks partitions 1-4 and floppy bootable
!	bit 7 = unlocked
! def:	bits 0-2 default boot partition (0-3, 4=floppy or 7=active)
!	bits 6,7 interrupt on (shift/ctrl,key press)
cfg_flags: set 0 ! No specially bootable partitions. Advanced mode disabled.
cfg_def:   set 7 ! Boot active partition, Interrupt by nothing.
cfg_delay: set 0
#endif

!
! We are loaded at 0:0x7c00 by the BIOS, but need to load boot sectors
! here, so we have got to move out of the way. We move to 0:DEST_ADDR
! 0x600 is as good a place as any.
#define LOAD_ADDR 0x7c00
#define DEST_ADDR 0x600
! The time when we started up.
stime	equ 0x800
.org DEST_ADDR
	! Do not use DL here; we need the value later.  It contains
	! the drive which the MBR was loaded from.
	cld
	xor ax,ax
	mov ss,ax
	xor sp,sp ! First word pushed goes to 0000:FFFE.
	mov ds,ax
	mov es,ax
	mov si,#LOAD_ADDR
#ifdef Y2KBUG
! We need dx and cx for locating and updating the MBR
	pusha	! MBR data: cx=cylinder/sector dx=head/drive si=address
#endif
	mov di,#DEST_ADDR ! Here will do
	mov cx,#0x100
	repz
	movsw
	mov si,#table+0x30 ! Set bootable flags from partition table
	mov al,#8 ! AH=0 is set from above
	jmp 0:cont ! Switch to the newly made copy. From now on labels work.
cont:
	cmpb drive,#0xFF ! If drive==0xFF, use the value in DL instead.
	jne ptloop
	mov drive,dl ! Now DL is free for use
ptloop:
	cmpb [si],#0 ! Check for bootable flag
	jz l7
	or flags,al ! Set in flags
l7:	sub si,#0x10
	shr al,1
	jnc ptloop ! Repeat until bit gets shifted out of al

	int 0x1a ! AH=0: Get time
	mov stime,dx

#ifdef Y2KBUG
! Address the year in the loaded copy.
#define YEAR #(year-DEST_ADDR+LOAD_ADDR)

	mov ah,#4
	int 0x1a	! cx=year(bcd) dh=month(bcd) dl=day(bcd)
	mov si,YEAR
	lodsw		! DF=0 set before
	cmp [si],dh	! compare last month, against this month
	pushf
	mov [si],dh
	jbe setdate	! if CF=1 jump
	inc ax		! we need to enter here with CF=0, inc doe not set it
	daa
	xchg ah,al
	adc al,#0
	daa
	xchg ah,al
	mov [si-2],ax
setdate:
	mov cx,ax
	mov ah,#5
	int 0x1a
	popf
	popa
	je nowrite
	mov bx,si
	mov ax,#0x0301
	int 0x13
nowrite:

#endif /* Y2KBUG */

#ifdef LOGO
	call show_logo
#endif

	cmp word[delay],#65535
	jz show_prompt ! Immediate interrupt
l0:	testb def,#0x80 ! Key press interrupt allowed
	jz l1
	mov ah,#1
	int 0x16
	jnz show_prompt ! Interrupted
l1:	testb def,#0x40 ! Shift/Ctrl allowed
	jz l2
	test byte 0x417,#0xf ! Check shift status
	jnz show_prompt ! Interrupted
l2:	xor ax,ax ! Check timer.
	int 0x1a
	sub dx,stime ! This code gets confused at midnight (FIXME)
	sub dx,delay
	jb l0 ! Time not passed

boot_def:
	mov al,def ! Boot default
	and al,#7
	cmp al,#7
	jnz boot2 ! Boot number al
	mov si,#table ! Boot first partition marked bootable
	mov al,#0
	mov cx,#4
l5:	cmpb [si],#0
boot2:	jnz boot
	inc al
	add si,#0x10
	loop l5 ! Try next partition

	! Display the prompt
show_prompt:
#ifdef TESTDISK
	xor bx,bx
#else /* TESTDISK */
#ifdef LOGO
	call show_logo
#else
	xor bx,bx
#endif
#endif /* TESTDISK */
	mov ah,#0xe ! Print char
	mov si,#chars ! List of chars to print
	mov cl,flags ! Interrupted (or no default)

l9:	lodsb
	shr cl,#1 ! Shift next bit into carry
	jnb l8
	int 0x10

l8:	or cl,cl ! Any more bits set?
	jnz l9
	mov al,#0x3a ! Print a colon
	int 0x10

wait_key:
	xor ax,ax ! Get user input
	int 0x16
	cmp al,#0
	jz wait_key ! Skip extended chars
#ifdef TESTDISK
	mov si, #crnl
	mov cx, #2
	call show_string
#endif /* TESTDISK */
	cmp al,#13 ! RETURN pressed
	jz boot_def ! Boot default
	cmp al,#'a ! CPP isn't quite compatible with as86
	jb l10
	cmp al,#'z ! ' This may make it a bit more obvious
	ja l10
	sub al,#0x20 ! Upper case input

l10:	mov bl,al
	mov si,#chars
	mov cl,flags

l12:	lodsb
	shr cl,#1
	jnb l13
	cmp bl,al
	jz l14
l13:	or cl,cl
	jnz l12
#ifdef TESTDISK
	jmp show_prompt
#else
	jmp wait_key
#endif

l14:	mov ax,#0xe0d
	xor bx,bx
	int 0x10
        ! FIXME: This could be shortened.
	lea ax, 0xff&-(chars+1)[si]
	cmp al,#7 ! Check if advanced mode selected
	jnz boot
	mov al,#0x1f
	mov flags,al
ishow_prompt:
	jmp show_prompt
	
boot:	! Boot partition al
#ifndef TESTDISK
#ifdef LOGO
	! Re-display the logo, so the prompt is right if we get an
	! error.
	call show_logo
#endif
#endif /* TESTDISK */
	xor dx,dx
	mov cx,#1
	cmp al,#4
	jz sread ! Boot from floppy (DL=0)
	jnb ishow_prompt ! Illegal - interrupt

	xor ah,ah
	mov cl,#4
	shl al,cl
	mov si,#table
	add si,ax
	mov dl,drive

	! Entry:
	!  SI -> Partition record
	!  DL = Drive number
sread:
	mov di,#5 ! number of retries
l6:
	push si
	test dl, #0x80		! Only try the extended interface on
#ifdef TESTDISK
	je odi			! hard disks.
#else
	je sdi			! hard disks.
#endif

	mov ah, #0x41
	mov bx, #0x55aa
	push dx
	int #0x13
	pop dx
	pop si
	push si
	jb sdi
	cmp bx, #0xaa55		! Check the signature
	jnz sdi
	test cl, #1		! Check the API support bitmap
	jz sdi

	! That will do.  The big disk extenstion is there.
	mov ax, 8[si]		
	mov bx, 10[si]
	mov si, #request
	mov 8[si], ax
	mov 10[si], bx
	mov ah, #0x42
	jmp cdi

	! Entry:
	!  SI -> Partition record
	!  DL = Drive number
	!  stack: si
sdi:
	mov dh,[si+1]
	mov cx,[si+2]
odi:
	! Entry:
	! DH = head
	! CX = cylinder/sector
	! DL = Drive number
	mov ax,#0x201
	mov bx,#LOAD_ADDR
cdi:
	push ax
	mov byte [request+2], #1	! Reset count to 1
	int 0x13
	pop ax
	pop si
	jnb lbit
	dec di
	jnz l6
iishow_prompt:
	jmp ishow_prompt
lbit:
	cmp 0x7dfe,#0xaa55
	jnz iishow_prompt
#ifndef TESTDISK
#ifdef LOGO
	! Start the next line.
	xor bx, bx
	mov ax, #0xe0d
	int 0x10
	mov al, #0xa
	int 0x10
#endif
#endif /* TESTDISK */
	jmp 0:LOAD_ADDR

#ifdef LOGO
	! Corrupts si, cx.  Returns with bx=0
show_logo:
	! Code to print the word "MBR" at boot time, to let people
	! know that we are here. - Tom Rothamel <tom-10990@onegeek.org>
	! Inspired by a discussion on debian-devel.
#ifdef TESTDISK
	mov si,#logo
	mov cx,#logolen
show_string:
	push ax
	mov ah,#0xe
	xor bx,bx
#else /* TESTDISK */
	push ax
	mov ax,#0xe0d ! Print char CR
	xor bx,bx
	int 0x10
	mov si,#logo
	mov cx,#logolen
#endif /* TESTDISK */	
logol:
	lodsb
	int 0x10
	loop logol
	pop ax
	ret

logo:
#ifdef TESTDISK
	.ascii "TestDisk"
crnl:
	db	0x0d, 0x0a
#else /* TESTDISK */
	.ascii "MBR "
#endif /* TESTDISK */
logo_end:
logolen equ logo_end-logo   ! The length of the logo string.
#endif

request:
	.byte 0x10, 0, 1, 0
	.word LOAD_ADDR, 0
	.word 0, 0, 0, 0
chars:
	db '1,'2,'3,'4,'F,0,0,'A

#ifndef NEW_FORMAT
	! The data area follows.  Access to this data area from
	! external code should be via the pointer at offset 0x1bc.
	! Check the signature and version numbers.  If the program
	! knows about version V, it may access the data if X<=V<=Y.
	! While the version is still 0.0, just check X against 0.0.
	!
	! There used to be 2 bytes for the version number.  I now see
	! this as overkill.  1 byte should be enough for the version
	! number.  The spare byte in the real version will be assembly
	! flags.  The spare byte in the compat version will be
	! reserved for future expansion.
data:	.ascii "NDTmbr" ! Sig string
	db 0 ! Free for use.
	db 2 ! From version X=2   i.e. Compat version
	db cfg_asm_flags
	db 2 ! To version Y=2     i.e. Real version
flags:	db cfg_flags
def:	db cfg_def
delay:	dw cfg_delay
drive:	db cfg_drive

padding:
#ifdef Y2KBUG
.space (DEST_ADDR+0x1b9)-padding
year:	dw 0x2001 ! Year
	db 1 ! Month
#else /* Y2KBUG */
.space (DEST_ADDR+0x1bc)-padding
#endif
	dw data-DEST_ADDR ! Pointer to the data
	
#else
	! The data area follows.  The area ends just before the
	! partition table, at 0x1b8. Check the signature and version
	! numbers.  The version is the real version of the structure
	! used.  It should be used to determine which fields are
	! valid.  When new fields are added we put them at the
	! beginning of the area.  This means that the old fields are
	! still where an old installer expects them.  We use the
	! compat_version field to tell the old installer that it is
	! allowed to use them.  If the old installer knows about the
	! compat_version, but not version, it may assume that there
	! are new fields, but the old fields are where it expects
	! them.
padding:
	.space 0x1ab-(padding - DEST_ADDR)
	! These are only valid on the Y2K version, but I cannot be
	! bothered removing them.
year:	dw 2001
month:	db 7
flags:	db cfg_flags
def:	db cfg_def
delay:	dw cfg_delay
drive:	db cfg_drive
	db cfg_asm_flags
	db 2 ! Compatible version.  Safe to access as v2.
	db 2 ! Real version.  This is v2.
	db 0xef, 0x17
! Disk signature
	.space 6
#endif
! Format of partition table entry
!   00 byte Boot indicator
!   01 byte start head
!   02 byte start sector
!   03 byte start cylinder
!   04 byte type
!   05 byte end head
!   06 byte end sector
!   07 byte end cylinder
!   08 dw   sectors before partition
!   0c dw   sectors in partition
table:	.space 0x40 ! The partition table
	dw 0xaa55

! Local Variables:
! mode:asm
! End: