boot.s

.code16
.align 4
BOOTSEG=0x07c0
INITSEG=0x9000

SETUPSEG=0x9020
SETUPLEN=4 

SYSSEG=0x1000
SYSLEN=17 #setup占用的磁道数

.globl start
.text
start:

# 将0x7c00处的bootsect读入到内存0x90000处
    mov $BOOTSEG, %ax
    mov %ax, %ds
    mov $INITSEG, %ax
    mov %ax, %es
    mov $256, %cx
    xor %si, %si
    xor %di, %di
    rep
    movsw
# 跳到0x90000处继续执行bootsect
    ljmp $INITSEG, $go

# 这里只做最基础的功能，并不考虑其他的问题（如书中提到的BIOS识别的最大软盘扇区是7）
go:
    mov %cs, %ax
    mov $0xfef4, %dx
    mov %ax, %ds
    mov %ax, %es 
    mov %ax, %ss
    mov %dx, %sp

# 将sectup读入到内存的0x90200
load_setup:
    xor %dx, %dx
    mov $0x0002, %cx
    mov $0x0200, %bx
    mov $0x0200+SETUPLEN, %ax
    int $0x13
    jnc ok_load_setup
# 读取setup失败
    xor %dx, %dx
    int $0x13
    jmp load_setup

ok_load_setup:
#读取每磁道的扇区数，保存在sectors中
    xor %dl, %dl
    mov $0x08, %ah
    int $0x13
    xor %ch, %ch
    mov %cx, sectors
# 恢复es寄存器
    mov $INITSEG, %ax
    mov %ax, %es
# 读取光标位置，保存在dx（dh行号，dl列号）
	mov $0x03, %ah
	xor %bh, %bh
	int $0x10
# 紧接着打印“Loading”字符串	
	mov $9, %cx
	mov $0x0007, %bx
	mov $msg1, %bp
	mov $0x1301, %ax
	int $0x10


# 读取system模块到0x10000处
	mov SYSSEG, %ax
	mov %ax, %es
	#call read_it
	call kill_motor
	
	# mov root_dev, %ax
	# or %ax, %ax
	# jne root_defined
	

# root_defined:
	# seg %cs
	# mov ax, root_dev, 

	ljmp $SETUPSEG, $0
# --------------------------------------------------------------------------------
kill_motor:
	push %dx
	mov $0x3f2, %dx
	xor %al, %al
	outb %al, %dx
	pop %dx
	ret
	
sectors:
	.word 0
	
msg1:
	.byte 13, 10
	.ascii "Loading"

.org 510
    .word 0xaa55