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#

# Copyright (C) 2001-2004 Jakub Jermar

# All rights reserved.

#

# Redistribution and use in source and binary forms, with or without

# modification, are permitted provided that the following conditions

# are met:

#

# - Redistributions of source code must retain the above copyright

#   notice, this list of conditions and the following disclaimer.

# - Redistributions in binary form must reproduce the above copyright

#   notice, this list of conditions and the following disclaimer in the

#   documentation and/or other materials provided with the distribution.

# - The name of the author may not be used to endorse or promote products

#   derived from this software without specific prior written permission.

#

# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#

# This is a very primitive boot.s

# It assumes that the first sector of the kernel image is found

# on head 0, track 0, sector 2 of the first floppy drive (1440K).

# Next kernel sectors follow on disk sector 3, 4, ...

#

.text

.global _start_0x7c00

.code16

_start_0x7c00:

	xorw %ax,%ax		# reset, %al will be used below

	movw %ax,%dx		# fd0, %dh and %dl will be used below

	int $0x13

	jc stop_trying

	movb $2,%ah		# read

	incb %al		# one sector

	movb %ah,%cl		# from disk sector 2

	movw %dx,%es

	movw $0x8000,%bx	# at %es:%bx

	int $0x13

	jc stop_trying

	pushw $('.')

	call echo_mark

	add $2,%sp

    	movw %dx,%ds

	# KERNEL_SIZE is passed from the outside to the preprocessor

	movl $(KERNEL_SIZE),%edi

	shrl $9,%edi		# number of sectors that kernel occupies (%edi div 512)

read_next:

	test %edi,%edi

	jnz read_sectors

	movb $12,%al

	movw $0x3f2,%dx

	outb %al,%dx

	pushw $('$')

	call echo_mark

	add $2,%sp	

	jmpl $0,$0x8000

read_sectors:

	pushw $('.')

	call echo_mark

	add $2,%sp

	decl %edi

	incw logical_sector

	movw %es,%si

	addw $0x20,%si

	movw %si,%es

	movw logical_sector,%ax

	divb sectors

	movb %ah,%cl

        incb %cl			# sector

	movb %al,%ch

	shrb $1,%ch			# track

	movb %al,%dh

	andb $1,%dh			# head

	movw $0x0201,%ax

	int $0x13

	jnc read_next

	pushw $('R')

	call echo_mark

	add $2,%sp

	xorw %ax,%ax			# try to reset

	movw %ax,%dx			# fd0

	int $0x13

	jnc read_next

stop_trying:

	pushw $('F')

	call echo_mark

	add $2,%sp

	cli

	hlt

CH=4

echo_mark:

	push %bp

	movw %sp,%bp

	pusha

	movw CH(%bp),%ax

	movb $0xe,%ah

	movb $7,%bl

	int $0x10

	popa

	pop %bp

	ret

# current logical sector from the beginning of the disk

logical_sector:

	.word 1

# number of sectors per track on 1440 floppy

sectors:

	.byte 18

# boot floppy signature

.org 0x1fe

boot_floppy_signature:

	.byte 0x55

	.byte 0xaa