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Rev 1 Rev 18
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# on head 0, track 0, sector 2 of the first floppy drive (1440K).
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# on head 0, track 0, sector 2 of the first floppy drive (1440K).
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# Next kernel sectors follow on disk sector 3, 4, ...
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# Next kernel sectors follow on disk sector 3, 4, ...
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#
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#
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- 
 
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# KERNEL_SIZE is passed from the outside to the preprocessor
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#if (KERNEL_SIZE%512>0)
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#define TAIL		1
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#else
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#define	TAIL		0
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#endif
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#define SECTORS		(KERNEL_SIZE/512+TAIL)
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.text
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.text
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.global _start_0x7c00
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.global _start_0x7c00
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.code16
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.code16
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_start_0x7c00:
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_start_0x7c00:
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	xorw %ax,%ax		# reset, %al will be used below
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	xorw %ax,%ax		# reset, %al will be used below
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	movw %ax,%dx		# fd0, %dh and %dl will be used below
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	movw %ax,%dx		# fd0, %dh and %dl will be used below
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	int $0x13
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	jc stop_trying
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    	movw %dx,%ds
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	movb $2,%ah		# read
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	incb %al		# one sector
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	movb %ah,%cl		# from disk sector 2
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	movw %dx,%ss		# initialize stack
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	movw %dx,%es
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	movw $stack,%sp
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	movw $0x8000,%bx	# at %es:%bx
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	int $0x13		# reset floppy
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	int $0x13
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	jc stop_trying
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	jc stop_trying
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	pushw $('.')
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	call echo_mark
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	add $2,%sp
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- 
 
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    	movw %dx,%ds
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    	movw %dx,%ds
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	movw %dx,%ss
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	movw $0x7c00,%sp
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	movw $0xffe0,%si	# after next increment, %si will become 0x0000
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	movw %si,%es
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	movw $0x8000,%bx	# at %es:%bx
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	# KERNEL_SIZE is passed from the outside to the preprocessor
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	movl $(KERNEL_SIZE),%edi
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	movl $(SECTORS),%edi
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	shrl $9,%edi		# number of sectors that kernel occupies (%edi div 512)
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- 
 
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read_next:
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read_next:
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	test %edi,%edi
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	test %edi,%edi
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	jnz read_sectors
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	jnz read_sectors
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	movb $12,%al
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	movb $12,%al
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	movw $0x3f2,%dx
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	movw $0x3f2,%dx
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	outb %al,%dx
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	outb %al,%dx
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	pushw $('$')
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	movb $('$'),%al
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	call echo_mark
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	call echo_mark
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	add $2,%sp
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	jmpl $0,$0x8000
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	jmpl $0,$0x8000
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read_sectors:
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read_sectors:
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	pushw $('.')
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	movb $('.'),%al
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	call echo_mark
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	call echo_mark
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	add $2,%sp
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	decl %edi
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	decl %edi
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	incw logical_sector
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	incw logical_sector
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	movw %es,%si
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	movw %es,%si
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	addw $0x20,%si
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	addw $0x20,%si
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	movw $0x0201,%ax
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	movw $0x0201,%ax
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	int $0x13
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	int $0x13
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	jnc read_next
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	jnc read_next
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	pushw $('R')
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	movb $('R'),%al
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	call echo_mark
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	call echo_mark
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	add $2,%sp
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	xorw %ax,%ax			# try to reset
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	xorw %ax,%ax			# try to reset
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	movw %ax,%dx			# fd0
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	movw %ax,%dx			# fd0
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	int $0x13
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	int $0x13
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	jnc read_next
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	jnc read_next
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stop_trying:
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stop_trying:
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	pushw $('F')
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	movb $('F'),%al
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	call echo_mark
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	call echo_mark
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	add $2,%sp
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	cli
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	cli
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	hlt
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	hlt
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CH=4
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CH=4
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echo_mark:
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echo_mark:
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	push %bp
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	push %bp
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	movw %sp,%bp
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	movw %sp,%bp
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	pusha
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	pusha
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	movw CH(%bp),%ax
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	movb $0xe,%ah
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	movb $0xe,%ah
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	movb $7,%bl
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	movb $7,%bl
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	int $0x10
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	int $0x10
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	popa
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	popa
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	pop %bp
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	pop %bp
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	ret
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	ret
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# current logical sector from the beginning of the disk
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# current logical sector from the beginning of the disk
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logical_sector:
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logical_sector:
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	.word 1
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	.word 0
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# number of sectors per track on 1440 floppy
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# number of sectors per track on 1440 floppy
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sectors:
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sectors:
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	.byte 18
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	.byte 18
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 - 
 
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# boot floppy signature
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# boot floppy signature
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.org 0x1fe
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.org 0x1fe
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boot_floppy_signature:
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boot_floppy_signature:
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	.byte 0x55
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	.byte 0x55
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	.byte 0xaa
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	.byte 0xaa
- 
 
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stack: