add directory kernel
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gohigh
274
kernel/0.1x/linux-0.10/boot/bootsect.sg
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274
kernel/0.1x/linux-0.10/boot/bootsect.sg
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/*
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*
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* bootsect.s (C) 1991 Linus Torvalds
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*
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* bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves
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* iself out of the way to address 0x90000, and jumps there.
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*
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* It then loads 'setup' directly after itself (0x90200), and the system
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* at 0x10000, using BIOS interrupts.
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*
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* NOTE! currently system is at most 8*65536 bytes long. This should be no
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* problem, even in the future. I want to keep it simple. This 512 kB
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* kernel size should be enough, especially as this doesn't contain the
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* buffer cache as in minix
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*
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* The loader has been made as simple as possible, and continuos
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* read errors will result in a unbreakable loop. Reboot by hand. It
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* loads pretty fast by getting whole sectors at a time whenever possible.
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*/
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.globl begtext, begdata, begbss, endtext, enddata, endbss
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.text
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begtext:
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.data
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begdata:
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.bss
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begbss:
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.text
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SETUPLEN = 4 # nr of setup-sectors
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BOOTSEG = 0x07c0 # original address of boot-sector
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INITSEG = 0x9000 # we move boot here - out of the way
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SETUPSEG = 0x9020 # setup starts here
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SYSSEG = 0x1000 # system loaded at 0x10000 (65536).
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ENDSEG = SYSSEG + SYSSIZE # where to stop loading
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/*
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* ROOT_DEV: 0x000 - same type of floppy as boot.
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* 0x301 - first partition on first drive etc
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*/
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ROOT_DEV = 0 # 0x306
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entry start
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start:
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mov $BOOTSEG,%ax
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mov %ax,%ds
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mov $INITSEG,%ax
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mov %ax,%es
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mov $256,%cx
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sub %si,%si
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sub %di,%di
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rep
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movw
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jmpi go,INITSEG
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go: mov %cs,%ax
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mov %ax,%ds
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mov %ax,%es
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/*
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* put stack at 0x9ff00.
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*/
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mov %ax,%ss
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mov $0xFF00,%sp # arbitrary value >>512
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/*
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* load the setup-sectors directly after the bootblock.
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* Note that 'es' is already set up.
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*/
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load_setup:
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mov $0x0000,%dx # drive 0, head 0
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mov $0x0002,%cx # sector 2, track 0
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mov $0x0200,%bx # address = 512, in INITSEG
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mov $0x0200,%ax+SETUPLEN # service 2, nr of sectors
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int 0x13 # read it
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jnc ok_load_setup # ok - continue
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mov $0x0000,%dx
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mov $0x0000,%ax # reset the diskette
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int 0x13
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j load_setup
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ok_load_setup:
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/*
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* Get disk drive parameters, specifically nr of sectors/track
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*/
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mov $0x00,%dl
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mov $0x0800,%ax # AH=8 is get drive parameters
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int 0x13
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mov $0x00,%ch
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seg %cs
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mov %cx,sectors
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mov $INITSEG,%ax
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mov %ax,%es
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/*
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* Print some inane message
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*/
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mov $0x03,%ah # read cursor pos
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xor %bh,%bh
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int 0x10
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mov $24,%cx
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mov $0x0007,%bx # page 0, attribute 7 (normal)
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mov $msg1,%bp
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mov $0x1301,%ax # write string, move cursor
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int 0x10
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/*
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* ok, we've written the message, now
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* we want to load the system (at 0x10000)
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*/
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mov $SYSSEG,%ax
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mov %ax,%es # segment of 0x010000
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call read_it
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call kill_motor
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/*
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* After that we check which root-device to use. If the device is
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* defined (!= 0), nothing is done and the given device is used.
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* Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending
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* on the number of sectors that the BIOS reports currently.
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*/
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seg %cs
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mov root,%ax_dev
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cmp %ax,$0
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jne root_defined
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seg %cs
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mov sectors,%bx
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mov $0x0208,%ax # /dev/ps0 - 1.2Mb
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cmp %bx,$15
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je root_defined
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mov $0x021c,%ax # /dev/PS0 - 1.44Mb
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cmp %bx,$18
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je root_defined
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undef_root:
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jmp undef_root
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root_defined:
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seg %cs
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mov root_%ax,dev
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/*
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* after that (everyting loaded), we jump to
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* the setup-routine loaded directly after
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* the bootblock:
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*/
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jmpi 0,SETUPSEG
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/*
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* This routine loads the system at address 0x10000, making sure
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* no 64kB boundaries are crossed. We try to load it as fast as
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* possible, loading whole tracks whenever we can.
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*
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* in: es - starting address segment (normally 0x1000)
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*
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*/
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sread: .word 1+SETUPLEN # sectors read of current track
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head: .word 0 # current head
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track: .word 0 # current track
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read_it:
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mov %es,%ax
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test %ax,$0x0fff
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die: jne die # %es must be at 64kB boundary
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xor %bx,%bx # %bx is starting address within segment
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rp_read:
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mov %es,%ax
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cmp %ax,$ENDSEG # have we loaded all yet?
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jb ok1_read
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ret
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ok1_read:
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seg %cs
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mov sectors,%ax
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sub sread,%ax
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mov %ax,%cx
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shl $9,%cx
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add %bx,%cx
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jnc ok2_read
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je ok2_read
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xor %ax,%ax
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sub %bx,%ax
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shr $9,%ax
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ok2_read:
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call read_track
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mov %ax,%cx
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add sread,%ax
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seg %cs
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cmp %ax,sectors
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jne ok3_read
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mov $1,%ax
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sub head,%ax
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jne ok4_read
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inc track
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ok4_read:
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mov %ax,head
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xor %ax,%ax
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ok3_read:
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mov %ax,sread
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shl $9,%cx
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add %cx,%bx
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jnc rp_read
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mov %es,%ax
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add $0x1000,%ax
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mov %ax,%es
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xor %bx,%bx
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jmp rp_read
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read_track:
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push %ax
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push %bx
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push %cx
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push %dx
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mov track,%dx
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mov sread,%cx
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inc %cx
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mov %dl,%ch
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mov head,%dx
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mov %dl,%dh
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mov $0,%dl
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and $0x0100,%dx
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mov $2,%ah
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int 0x13
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jc bad_rt
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pop %dx
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pop %cx
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pop %bx
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pop %ax
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ret
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bad_rt: mov %ax,$0
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mov $0,%dx
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int 0x13
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pop %dx
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pop %cx
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pop %bx
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pop %ax
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jmp read_track
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/*
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* This procedure turns off the floppy drive motor, so
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* that we enter the kernel in a known state, and
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* don't have to worry about it later.
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*/
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kill_motor:
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push %dx
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mov $0x3f2,%dx
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mov $0,%al
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outb
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pop %dx
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ret
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sectors:
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.word 0
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msg1:
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.byte 13,10
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.ascii "Loading system ..."
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.byte 13,10,13,10
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.org 508
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root_dev:
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.word ROOT_DEV
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boot_flag:
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.word 0xAA55
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.text
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endtext:
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.data
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enddata:
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.bss
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endbss:
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