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bootsect.S 2.68 KB
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hinus 提交于 2021-07-08 22:42 . Title: Read data from floppy.
SYSSIZE = 0x3000
SETUPLEN = 4
BOOTSEG = 0x7c0
INITSEG = 0x9000
SETUPSEG = 0x9020
SYSSEG = 0x1000
ENDSEG = SYSSEG + SYSSIZE
ROOT_DEV = 0x000
.code16
.text
.global _start
_start:
jmpl $BOOTSEG, $start2
start2:
movw $BOOTSEG, %ax
movw %ax, %ds
movw $INITSEG, %ax
movw %ax, %es
movw $256, %cx
subw %si, %si
subw %di, %di
rep
movsw
jmpl $INITSEG, $go
go:
movw %cs, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %ss
movw $0xFF00, %sp
load_setup:
movw $0x0000, %dx
movw $0x0002, %cx
movw $0x0200, %bx
movb $0x02, %ah
movb $SETUPLEN, %al
int $0x13
jnc ok_load_setup
movw $0x0000, %dx
movw $0x0000, %ax
int $0x13
jmp load_setup
ok_load_setup:
movb $0x00, %dl
movw $0x0800, %ax
int $0x13
movb $0x00, %ch
movw %cx, %cs:sectors
movw $INITSEG, %ax
movw %ax, %es
movw $SYSSEG, %ax
movw %ax, %es
call read_it
call kill_motor
movw %cs:root_dev, %ax
cmpw $0, %ax
jne root_defined
movw %cs:sectors, %bx
movw $0x0208, %ax
cmpw $15, %bx
je root_defined
movw $0x021c, %ax
cmpw $18, %bx
je root_defined
undef_root:
jmp undef_root
root_defined:
mov %ax, %cs:root_dev
movw %cs, %ax
movw %ax, %ds
movw %ax, %es
movw $0x600, %ax
movw $0x700, %bx
movw $0x0, %cx
movw $0x184f,%dx
int $0x10
movw $msg, %ax
movw %ax, %bp
movw $0x01301, %ax
movw $0x0c, %bx
movw $23, %cx
movw $0, %dx
int $0x010
jmpl $SETUPSEG, $0
sread:
.word 1+SETUPLEN
head:
.word 0
track:
.word 0
read_it:
movw %es, %ax
testw $0x0fff, %ax
die:
jne die
xor %bx, %bx
rp_read:
movw %es, %ax
cmpw $ENDSEG, %ax
jb ok1_read
ret
ok1_read:
movw %cs:sectors, %ax
subw sread, %ax
movw %ax, %cx
shlw $9, %cx
addw %bx, %cx
jnc ok2_read
je ok2_read
xorw %ax, %ax
subw %bx, %ax
shrw $9, %ax
ok2_read:
call read_track
movw %ax, %cx
addw sread, %ax
cmpw %cs:sectors, %ax
jne ok3_read
movw $1, %ax
subw head, %ax
jne ok4_read
incw track
ok4_read:
movw %ax, head
xorw %ax, %ax
ok3_read:
movw %ax, sread
shlw $9, %cx
addw %cx, %bx
jnc rp_read
movw %es, %ax
addw $0x1000, %ax
movw %ax, %es
xorw %bx, %bx
jmp rp_read
read_track:
pushw %ax
pushw %bx
pushw %cx
pushw %dx
movw track, %dx
movw sread, %cx
incw %cx
movb %dl, %ch
movw head, %dx
movb %dl, %dh
movb $0, %dl
andw $0x0100, %dx
movb $2, %ah
int $0x13
jc bad_rt
popw %dx
popw %cx
popw %bx
popw %ax
ret
bad_rt:
movw $0x0, %ax
movw $0x0, %dx
int $0x13
popw %dx
popw %cx
popw %bx
popw %ax
jmp read_track
kill_motor:
pushw %dx
movw $0x3f2, %dx
movb $0, %al
outb %al, %dx
popw %dx
ret
sectors:
.word 0
msg:
.byte 13, 10
.ascii "Linux is booting..."
.byte 13, 10
.org 508
root_dev:
.word ROOT_DEV
boot_flag:
.word 0xaa55
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