dosstart.s

grub4dos-0.4.4-2008- 08-src.zip

	shll	$6, %edx			# and go from 64k to 1k chunks
	movl	%edx, (0x1e0)			# store extended memory size
	andl	$0xffff, %ecx			# clear sign extend
 	addl	%ecx, (0x1e0)			# and add lower memory into
						# total size.

# Ye Olde Traditional Methode.  Returns the memory size (up to 16mb or
# 64mb, depending on the bios) in ax.
mem88:

#endif
	movb	$0x88, %ah
	int	$0x15
	movw	%ax, (2)

get_mem_size_end: 

# Set the keyboard repeat rate to the max
	movw	$0x0305, %ax
	xorw	%bx, %bx
	int	$0x16

#; grub4dos needn't get video, hd, mouse, APM, edd
#;	jmp	get_misc_info_end
#;
#;# Check for video adapter and its parameters and allow the
#;# user to browse video modes.
#;	call	video				# NOTE: we need %ds pointing
#;						# to bootsector
#;
#;# Get hd0 data...
#;	xorw	%ax, %ax
#;	movw	%ax, %ds
#;	ldsw	(4 * 0x41), %si
#;	movw	%cs, %ax			# aka SETUPSEG
#;	subw	$DELTA_INITSEG, %ax		# aka INITSEG
#;	pushw	%ax
#;	movw	%ax, %es
#;	movw	$0x0080, %di
#;	movw	$0x10, %cx
#;	pushw	%cx
#;	cld
#;	rep
#; 	movsb
#;# Get hd1 data...
#;	xorw	%ax, %ax
#;	movw	%ax, %ds
#;	ldsw	(4 * 0x46), %si
#;	popw	%cx
#;	popw	%es
#;	movw	$0x0090, %di
#;	rep
#;	movsb
#;# Check that there IS a hd1 :-)
#;	movw	$0x01500, %ax
#;	movb	$0x81, %dl
#;	int	$0x13
#;	jc	no_disk1
#;	
#;	cmpb	$3, %ah
#;	je	is_disk1
#;
#;no_disk1:
#;	movw	%cs, %ax			# aka SETUPSEG
#;	subw	$DELTA_INITSEG, %ax 		# aka INITSEG
#;	movw	%ax, %es
#;	movw	$0x0090, %di
#;	movw	$0x10, %cx
#;	xorw	%ax, %ax
#;	cld
#;	rep
#;	stosb
#;is_disk1:
#;# check for Micro Channel (MCA) bus
#;	movw	%cs, %ax			# aka SETUPSEG
#;	subw	$DELTA_INITSEG, %ax		# aka INITSEG
#;	movw	%ax, %ds
#;	xorw	%ax, %ax
#;	movw	%ax, (0xa0)			# set table length to 0
#;	movb	$0xc0, %ah
#;	stc
#;	int	$0x15				# moves feature table to es:bx
#;	jc	no_mca
#;
#;	pushw	%ds
#;	movw	%es, %ax
#;	movw	%ax, %ds
#;	movw	%cs, %ax			# aka SETUPSEG
#;	subw	$DELTA_INITSEG, %ax		# aka INITSEG
#;	movw	%ax, %es
#;	movw	%bx, %si
#;	movw	$0xa0, %di
#;	movw	(%si), %cx
#;	addw	$2, %cx				# table length is a short
#;	cmpw	$0x10, %cx
#;	jc	sysdesc_ok
#;
#;	movw	$0x10, %cx			# we keep only first 16 bytes
#;sysdesc_ok:
#;	rep
#;	movsb
#;	popw	%ds
#;no_mca:
#;#ifdef CONFIG_X86_VOYAGER
#;	movb	$0xff, 0x40	# flag on config found
#;	movb	$0xc0, %al
#;	mov	$0xff, %ah
#;	int	$0x15		# put voyager config info at es:di
#;	jc	no_voyager
#;	movw	$0x40, %si	# place voyager info in apm table
#;	cld
#;	movw	$7, %cx
#;voyager_rep:
#;	movb	%es:(%di), %al
#;	movb	%al,(%si)
#;	incw	%di
#;	incw	%si
#;	decw	%cx
#;	jnz	voyager_rep
#;no_voyager:	
#;#endif
#;# Check for PS/2 pointing device
#;	movw	%cs, %ax			# aka SETUPSEG
#;	subw	$DELTA_INITSEG, %ax		# aka INITSEG
#;	movw	%ax, %ds
#;	movw	$0, (0x1ff)			# default is no pointing device
#;	int	$0x11				# int 0x11: equipment list
#;	testb	$0x04, %al			# check if mouse installed
#;	jz	no_psmouse
#;
#;	movw	$0xAA, (0x1ff)			# device present
#;no_psmouse:
#;
#;#if defined(CONFIG_X86_SPEEDSTEP_SMI) || defined(CONFIG_X86_SPEEDSTEP_SMI_MODULE)
#;	movl	$0x0000E980, %eax		# IST Support 
#;	movl	$0x47534943, %edx		# Request value
#;	int	$0x15
#;
#;	movl	%eax, (96)
#;	movl	%ebx, (100)
#;	movl	%ecx, (104)
#;	movl	%edx, (108)
#;#endif
#;
#;#if defined(CONFIG_APM) || defined(CONFIG_APM_MODULE)
#;# Then check for an APM BIOS...
#;						# %ds points to the bootsector
#;	movw	$0, 0x40			# version = 0 means no APM BIOS
#;	movw	$0x05300, %ax			# APM BIOS installation check
#;	xorw	%bx, %bx
#;	int	$0x15
#;	jc	done_apm_bios			# Nope, no APM BIOS
#;	
#;	cmpw	$0x0504d, %bx			# Check for "PM" signature
#;	jne	done_apm_bios			# No signature, no APM BIOS
#;
#;	andw	$0x02, %cx			# Is 32 bit supported?
#;	je	done_apm_bios			# No 32-bit, no (good) APM BIOS
#;
#;	movw	$0x05304, %ax			# Disconnect first just in case
#;	xorw	%bx, %bx
#;	int	$0x15				# ignore return code
#;	movw	$0x05303, %ax			# 32 bit connect
#;	xorl	%ebx, %ebx
#;	xorw	%cx, %cx			# paranoia :-)
#;	xorw	%dx, %dx			#   ...
#;	xorl	%esi, %esi			#   ...
#;	xorw	%di, %di			#   ...
#;	int	$0x15
#;	jc	no_32_apm_bios			# Ack, error. 
#;
#;	movw	%ax,  (66)			# BIOS code segment
#;	movl	%ebx, (68)			# BIOS entry point offset
#;	movw	%cx,  (72)			# BIOS 16 bit code segment
#;	movw	%dx,  (74)			# BIOS data segment
#;	movl	%esi, (78)			# BIOS code segment lengths
#;	movw	%di,  (82)			# BIOS data segment length
#;# Redo the installation check as the 32 bit connect
#;# modifies the flags returned on some BIOSs
#;	movw	$0x05300, %ax			# APM BIOS installation check
#;	xorw	%bx, %bx
#;	xorw	%cx, %cx			# paranoia
#;	int	$0x15
#;	jc	apm_disconnect			# error -> shouldn't happen
#;
#;	cmpw	$0x0504d, %bx			# check for "PM" signature
#;	jne	apm_disconnect			# no sig -> shouldn't happen
#;
#;	movw	%ax, (64)			# record the APM BIOS version
#;	movw	%cx, (76)			# and flags
#;	jmp	done_apm_bios
#;
#;apm_disconnect:					# Tidy up
#;	movw	$0x05304, %ax			# Disconnect
#;	xorw	%bx, %bx
#;	int	$0x15				# ignore return code
#;
#;	jmp	done_apm_bios
#;
#;no_32_apm_bios:
#;	andw	$0xfffd, (76)			# remove 32 bit support bit
#;done_apm_bios:
#;#endif
#;
#;#include "edd.S"
#;
#;get_misc_info_end:

# Now we want to move to protected mode ...
	cmpw	$0, %cs:realmode_swtch - start
	jz	rmodeswtch_normal

	lcall	*%cs:realmode_swtch - start

	jmp	rmodeswtch_end

rmodeswtch_normal:
	pushw	%cs
	call	default_switch

rmodeswtch_end:
# we get the code32 start address and modify the below 'jmpi'
# (loader may have changed it)
	movl	%cs:code32_start - start, %eax
	movl	%eax, %cs:code32 - start

# Now we move the system to its rightful place ... but we check if we have a
# big-kernel. In that case we *must* not move it ...
	testb	$LOADED_HIGH, %cs:loadflags - start
	jz	do_move0			# .. then we have a normal low
						# loaded zImage
						# .. or else we have a high
						# loaded bzImage
	jmp	end_move			# ... and we skip moving

do_move0:
	movw	$0x100, %ax			# start of destination segment
	movw	%cs, %bp			# aka SETUPSEG
	subw	$DELTA_INITSEG, %bp		# aka INITSEG
	movw	%cs:start_sys_seg - start, %bx	# start of source segment
	cld
do_move:
	movw	%ax, %es			# destination segment
	incb	%ah				# instead of add ax,#0x100
	movw	%bx, %ds			# source segment
	addw	$0x100, %bx
	subw	%di, %di
	subw	%si, %si
	movw 	$0x800, %cx
	rep
	movsw
	cmpw	%bp, %bx			# assume start_sys_seg > 0x200,
						# so we will perhaps read one
						# page more than needed, but
						# never overwrite INITSEG
						# because destination is a
						# minimum one page below source
	jb	do_move

end_move:
# then we load the segment descriptors
	movw	%cs, %ax			# aka SETUPSEG
	movw	%ax, %ds
		
# Check whether we need to be downward compatible with version <=201
	cmpl	$0, cmd_line_ptr - start
	jne	end_move_self		# loader uses version >=202 features
	cmpb	$0x20, type_of_loader - start
	je	end_move_self		# bootsect loader, we know of it

# Boot loader doesnt support boot protocol version 2.02.
# If we have our code not at 0x90000, we need to move it there now.
# We also then need to move the params behind it (commandline)
# Because we would overwrite the code on the current IP, we move
# it in two steps, jumping high after the first one.
	movw	%cs, %ax
	cmpw	$SETUPSEG, %ax
	je	end_move_self

	cli					# make sure we really have
						# interrupts disabled !
						# because after this the stack
						# should not be used
	subw	$DELTA_INITSEG, %ax		# aka INITSEG
	movw	%ss, %dx
	cmpw	%ax, %dx
	jb	move_self_1

	addw	$INITSEG, %dx
	subw	%ax, %dx			# this will go into %ss after
						# the move
move_self_1:
	movw	%ax, %ds
	movw	$INITSEG, %ax			# real INITSEG
	movw	%ax, %es
	movw	%cs:setup_move_size - start, %cx
	std					# we have to move up, so we use
						# direction down because the
						# areas may overlap
	movw	%cx, %di
	decw	%di
	movw	%di, %si
	subw	$(move_self_here - start+0x200), %cx
	rep
	movsb
	ljmp	$SETUPSEG, $(move_self_here - start)

move_self_here:
	movw	$(move_self_here - start+0x200), %cx
	rep
	movsb
	movw	$SETUPSEG, %ax
	movw	%ax, %ds
	movw	%dx, %ss
end_move_self:					# now we are at the right place

#
# Enable A20.  This is at the very best an annoying procedure.
# A20 code ported from SYSLINUX 1.52-1.63 by H. Peter Anvin.
# AMD Elan bug fix by Robert Schwebel.
#
	movw	$(a20_control_begin_string - start), %si
	call	prtstr

	movw	$0x00ff, %cx		# try so many times on failure
	movw	$0x0101, %dx		# non-zero means `enable'
	call	enable_disable_a20
	jz	3f
	movw	$(a20_control_fail_string - start), %si
	call	prtstr
1:
	hlt
	jmp	1b
3:
	movw	$(a20_control_ok_string - start), %si
	call	prtstr

# set up gdt and idt
	lidt	idt_48 - start			# load idt with 0,0
	xorl	%eax, %eax			# Compute gdt_base
	movw	%ds, %ax			# (Convert %ds:gdt to a linear ptr)
	shll	$4, %eax
	addl	$gdt - start, %eax
	movl	%eax, (gdt_48 - start+2)
	lgdt	gdt_48 - start			# load gdt with whatever is
						# appropriate

# make sure any possible coprocessor is properly reset..
	xorw	%ax, %ax
	outb	%al, $0xf0
	call	delay

	outb	%al, $0xf1
	call	delay

# well, that went ok, I hope. Now we mask all interrupts - the rest
# is done in init_IRQ().
	movb	$0xFF, %al			# mask all interrupts for now
	outb	%al, $0xA1
	call	delay
	
	movb	$0xFB, %al			# mask all irq's but irq2 which
	outb	%al, $0x21			# is cascaded

# Well, that certainly wasn't fun :-(. Hopefully it works, and we don't
# need no steenking BIOS anyway (except for the initial loading :-).
# The BIOS-routine wants lots of unnecessary data, and it's less
# "interesting" anyway. This is how REAL programmers do it.
#
# Well, now's the time to actually move into protected mode. To make
# things as simple as possible, we do no register set-up or anything,
# we let the gnu-compiled 32-bit programs do that. We just jump to
# absolute address 0x1000 (or the loader supplied one),
# in 32-bit protected mode.
#
# Note that the short jump isn't strictly needed, although there are
# reasons why it might be a good idea. It won't hurt in any case.
	movw	$1, %ax				# protected mode (PE) bit
	lmsw	%ax				# This is it!
	jmp	flush_instr

flush_instr:
	xorw	%bx, %bx			# Flag to indicate a boot
	xorl	%esi, %esi			# Pointer to real-mode code
	movw	%cs, %si
	subw	$DELTA_INITSEG, %si
	shll	$4, %esi			# Convert to 32-bit pointer

# jump to startup_32 in arch/i386/boot/compressed/head.S
#	
# NOTE: For high loaded big kernels we need a
#	jmpi    0x100000,__BOOT_CS
#
#	but we yet haven't reloaded the CS register, so the default size 
#	of the target offset still is 16 bit.
#	However, using an operand prefix (0x66), the CPU will properly
#	take our 48 bit far pointer. (INTeL 80386 Programmer's Reference
#	Manual, Mixing 16-bit and 32-bit code, page 16-6)

	.byte 0x66, 0xea			# prefix + jmpi-opcode
code32:	.long	0x1000				# will be set to 0x100000
						# for big kernels
	.word	__BOOT_CS

# Here's a bunch of information about your current kernel..
kernel_version:	.ascii	UTS_RELEASE
		.ascii	" ("
		.ascii	LINUX_COMPILE_BY
		.ascii	"@"
		.ascii	LINUX_COMPILE_HOST
		.ascii	") "
		.ascii	UTS_VERSION
		.byte	0

# This is the default real mode switch routine.
# to be called just before protected mode transition
default_switch:
	cli					# no interrupts allowed !
	movb	$0x80, %al			# disable NMI for bootup
						# sequence
	outb	%al, $0x70
	lret

#-----------------------------------------------------------------------------
#	DOS device driver and EXE will use this code to enable/disable A20
#-----------------------------------------------------------------------------

	// to asure the command-line menu will not overwrite our code here

	. = start + 0x1000 + 0x82 + (. - (start + 0x1000 + 0x82)) * (1 & (. > (start + 0x1000 + 0x82)))

	. = . - ((0x1000 + 0x81) / (. - start))

	/* print ASCIZ string DS:SI (modifies AX BX SI) */
1:
	xorw	%bx, %bx	/* video page 0 */
	movb	$0x0e, %ah	/* print char in AL */
	int	$0x10		/* via TTY mode */

prtstr:

	lodsb			/* get token */
	cmpb	$0, %al		/* end of string? */
	jne	1b
	ret

//# Routine to print asciiz string at ds:si
//prtstr: