261 lines
7.4 KiB
NASM
261 lines
7.4 KiB
NASM
BaseOfBoot equ 1000h ; 段地址，mbr加载loader到这个段
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OffsetOfBoot equ 7c00h ; load Boot sector to BaseOfBoot:OffsetOfBoot
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OffsetOfActiPartStartSec equ 7e00h ; 活动分区的起始扇区号相对于BaseOfBoot的偏移量 ;added by mingxuan 2020-9-12
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; 该变量来自分区表，保存在该内存地址，用于在os_boot和loader中查找FAT32文件
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org 07c00h
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LABEL_START:
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mov ax, cs
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mov ds, ax
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mov es, ax
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mov ss, ax
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mov sp, 7c00h
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; 清屏
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mov ax, 0600h ; AH = 6, AL = 0h
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mov bx, 0700h ; 黑底白字(BL = 07h)
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mov cx, 0 ; 左上角: (0, 0)
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mov dx, 0184fh ; 右下角: (80, 50)
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int 10h ; int 10h
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mov dh, 0 ;
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call DispStr ;
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xor ah, ah ; ┓
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xor dl, dl ; ┣ 软驱复位
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int 13h ; ┛
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;循环读取分区表
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mov bx, 0 ;每次循环累加16
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mov dh, 1 ;每次循环累加1
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jmp CHECK_PARTITION ;added by mingxuan 2020-9-29
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;added by mingxuan 2020-9-29
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LABLE_END_EXTENDED:
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mov byte [EndInExt], 0 ;将EndInExt置0，复位
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; 检查扩展分区表的第二项是否是空项。如果是空项则表明当前逻辑分区就是最后一个。
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add bx, 16
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mov cl, [es:7c00h+446+bx+4] ;分区类型
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;sub bx, 16 ;deleted by mingxuan 2020-9-30
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cmp cl, 0
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jz RESET_SecOffset_SELF
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CHECK_PARTITION:
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mov dl, [es:7c00h+446+bx] ;分区活跃标志地址
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;mov ax, word [es:7c00h+446+bx+8] ;分区起始扇区地址 ;deletd by mingxuan 2020-9-12
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mov eax, dword [es:7c00h+446+bx+8] ;分区起始扇区地址 ;modified by mingxuan 2020-9-12
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;修改为eax的原因: 分区表用4个字节来表示起始扇区，而不是2个字节, mingxuan
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;add ax, [SecOffset] ;deletd by mingxuan 2020-9-12
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;add eax, [SecOffset] ;modified by mingxuan 2020-9-29
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;deleted by mingxuan 2020-9-29
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mov cl, [es:7c00h+446+bx+4] ;分区类型
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cmp cl, 5 ;extended partition type = 5
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;jz LABLE_EXTENDED
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jz LABLE_IN_EXTENDED ;modified by mingxuan 2020-9-29
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add eax, [SecOffset_SELF] ;added by mingxuan 2020-9-29
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add byte [CurPartNo], 1
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add byte [CurPartNum], 1 ; added by mingxuan 2020-9-29 ;deleted by mingxuan 2020-9-30
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cmp dl, 80h
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jz LABLE_ACTIVE
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; 检查当前的分区表是否是扩展分区的最后一个逻辑分区
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mov cl, [EndInExt]
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cmp cl, 1 ;added by mingxuan 2020-9-29
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jz LABLE_END_EXTENDED ;added by mingxuan 2020-9-29
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cmp dh, 4
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jz LABLE_NOT_FOUND
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inc dh
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add bx, 16
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jmp CHECK_PARTITION
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RESET_SecOffset_SELF:
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; SecOffset_SELF置0的目的是以后又恢复到搜索主分区
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mov edx, 0
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mov [SecOffset_SELF], edx
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mov dl, [EXTNum]
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mov al, 16
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mul dl
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mov bx, ax
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mov ax, 0 ;added by mingxuan 2020-9-30
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mov es, ax ;added by mingxuan 2020-9-30
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jmp CHECK_PARTITION
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; added by mingxuan 2020-9-29
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LABLE_IN_EXTENDED: ;在分区表中发现扩展分区后，跳转到这里来执行
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; 此时的eax有两种情况：
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; 1) 当第一次执行该程序时，eax是从主分区表里获得的扩展分区起始的绝对地址
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; 2) 之后的执行, eax是从扩展分区表的第二项获得的起始地址(相对于整个扩展分区起始地址偏移量)
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; 从扩展分区表的第二项获得的起始地址是相对于整个扩展分区起始地址偏移量，所以要加上基地址
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; 特殊情况: 当第一次进入该过程时，SecOffset_EXT的值是0。此时是从主分区表里获得的起始地址，这个地址是绝对地址。
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add eax, [SecOffset_EXT] ;modified by mingxuan 2020-9-29
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; FirstInExt是标志位，判断是否是第一次进入该过程
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mov cl, [FirstInExt]
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; 若为1，表示不是第一次进入该过程。
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cmp cl, 1
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jz LABLE_EXTENDED
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; 以下是第一次进入该过程要执行的语句（仅执行一遍）
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; 要记录下扩展分区是主分区表的第几项
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add byte [CurPartNum], 1 ;added by mingxuan 2020-9-30
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mov cl, [CurPartNum]
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mov [EXTNum], cl
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; 当第一次进入该过程时，要记录下扩展分区的起始地址，该地址是以后所有逻辑分区的偏移量的基地址
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mov [SecOffset_EXT], eax
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mov byte [FirstInExt], 1
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LABLE_EXTENDED:
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;mov [SecOffset], ax ;deleted by mingxuan 2020-9-12
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;mov [SecOffset], eax ;deleted by mingxuan 2020-9-12
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;要记录下每个逻辑分区的起始地址，因为每次找自身时需要用这个地址做基地址。（该变量每次都要更新）
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mov [SecOffset_SELF], eax ;added by mingxuan 2020-9-29
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add byte [EbrNum], 1
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cmp byte [EbrNum], 1
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jz ._add_CurPartNo
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._read_ebr:
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mov cl, 1
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mov bx, BaseOfBoot
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mov es, bx
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mov bx, OffsetOfBoot
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call ReadSector
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mov bx, 0
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mov dh, 1
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; 将EndInExt置1，表示此时正在扫描扩展分区，用于之后程序判断当前是否是扩展分区的终点
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mov [EndInExt], dh ;added by mingxuan 2020-9-29
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jmp CHECK_PARTITION
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._add_CurPartNo:
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add byte [CurPartNo], 1
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jmp ._read_ebr
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LABLE_ACTIVE:
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mov cl, 1 ;要读取的扇区个数
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mov bx, BaseOfBoot
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mov es, bx
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mov dword [es:OffsetOfActiPartStartSec], eax ;此时eax中存放活动分区的起始扇区号
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;added by mingxuan 2020-9-12
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mov bx, OffsetOfBoot ;对应扇区会被加载到内存的 es:bx 处
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call ReadSector
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;mov dh, 1
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;call DispStr
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;mov dh, 2
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;call DispStr
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; mov ah,0h
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; int 16h
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jmp BaseOfBoot:OffsetOfBoot
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LABLE_NOT_FOUND:
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mov dh, 3
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call DispStr
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jmp $
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;SecOffset dw 0 ;deletd by mingxuan 2020-9-12
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;SecOffset dd 0 ;modifed by mingxuan 2020-9-29
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SecOffset_SELF dd 0 ;modifed by mingxuan 2020-9-29
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SecOffset_EXT dd 0 ;modifed by mingxuan 2020-9-29
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EbrNum db 0
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FirstInExt db 0 ;added by mingxuan 2020-9-29
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EndInExt db 0 ;added by mingxuan 2020-9-29
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EXTNum db 0 ;added by mingxuan 2020-9-29
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CurPartNum db 0 ;added by mingxuan 2020-9-29
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MessageLength equ 27
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BootMessage: db "Finding active partition..." ; 27字节, 不够则用空格补齐. 序号 0
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Message1 db " partition "
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CurPartNo db "0"
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db ": active"
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;Message2 db "press any key to continue "
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Message3 db "active partition not found!"
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DispStr:
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push ax
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push dx
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mov ax, MessageLength
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mul dh
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add ax, BootMessage
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mov bp, ax ; ┓
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mov ax, ds ; ┣ ES:BP = 串地址
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mov es, ax ; ┛
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mov cx, MessageLength ; CX = 串长度
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mov ax, 01301h ; AH = 13, AL = 01h
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mov bx, 0007h ; 页号为0(BH = 0) 黑底白字(BL = 07h)
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mov dl, 0
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int 10h ; int 10h
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pop dx
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pop ax
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ret
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;----------------------------------------------------------------------------
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; 函数名: ReadSector (使用扩展int13 ah=42)
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;----------------------------------------------------------------------------
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; 作用:
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; 从第 ax 个 Sector 开始, 将 cl 个 Sector 读入 es:bx 中
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DAPS:
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DB 0x10 ; size of packet
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DB 0 ; Always 0
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D_CL DW 1 ; number of sectors to transfer
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D_BX DW OffsetOfBoot ; transfer buffer (16 bit segment:16 bit offset)
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D_ES DW BaseOfBoot
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LBA_Lo DD 1 ; lower 32-bits of 48-bit starting LBA
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LBA_Hi DD 0 ; upper 32-bits of 48-bit starting LBAs
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ReadSector:
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mov [D_CL], cl
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mov [D_BX], bx
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mov [D_ES], es
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;mov [LBA_Lo], ax ;deleted by mingxuan 2020-9-17
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mov [LBA_Lo], eax ;modified by mingxuan 2020-9-17
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;修改为eax的原因: 分区表用4个字节来表示起始扇区，而不是2个字节, mingxuan
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mov dl, 0x80
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.GoOnReading:
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mov ah, 42h
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mov si, DAPS
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int 13h
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jc .GoOnReading ; 如果读取错误 CF 会被置为 1, 这时就不停地读, 直到正确为止
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ret
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times 444 -($-$$) db 0
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dw 0x0000 |