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                <td><span id="ArticleContent1_ArticleContent1_lblContent"><p>;====================================================================<br>; <br>; FlyingDragon OS Boot Sector FOR FAT32<br>;<br>; Author: Jack<br>; V0.01 2005-07-23 17:39<br>; V0.02&nbsp;2005-08-07 09:29<br>; <br>; Build : nasm -f bin FAT32.ASM -oFAT32.BIN&nbsp;<br>; &nbsp;<br>;====================================================================================<br>; <br>; BIOS在啟動中的角色:<br>; &nbsp;(1) BIOS裝載引導驅動器上的0扇區(CHS = 0:0:1)內容到內存線性地址7C00H處；<br>; &nbsp;(2) BIOS檢查所裝載的扇區是否有啟動標記(510、511字節分別為55H和AAH)； <br>; &nbsp;(3) CPU寄存器DL被設置為分配給引導驅動器的驅動器號，00H為軟驅A，80H為硬盤C；<br>; &nbsp;(4) BIOS跳轉到其裝載的扇區中的代碼(即7C00H處)，將控制權轉交給引導代碼。<br>; <br>; 引導代碼應該初始化以下寄存器：<br>; &nbsp;(1) DS：某些BIOS設置其值為0，某些設置其為40H，它應該被設置為(7C00H-BOOT_ORG)/16；<br>; &nbsp;&nbsp;其中，BOOT_ORG為引導代碼的ORG值，該值通常為7C00H(這意味著DS應設置為0);<br>; &nbsp;(2) SS和SP(堆棧)：這兩個寄存器的初始值依賴于BIOS；<br>; &nbsp;(3) CS個IP(通過JMP指令)：大多數的BIOS進入啟動代碼的地址為0000:7C00H，但是某些<br>; &nbsp;&nbsp;BIOS卻跳轉到07C0:0000H。由于短跳轉和條件跳轉是IP相關的，因此如果沒有使用<br>;&nbsp;&nbsp;遠跳轉或者絕對跳轉，則不需要重置CS和IP；然而，DS仍舊必須是正確的值。<br>; <br>;=====================================================================================<br>; <br>; 常規內存( 0000 0000H - 000F FFFFH，即0-1MB )在系統啟動時的使用情況<br>; <br>;=====================================================================================<br>; <br>; &nbsp;&nbsp;---------------------------------<br>; &nbsp;&nbsp;|&nbsp;0000 0000 - 0000 03FF&nbsp;&nbsp; &nbsp;|&nbsp;1024B&nbsp; &nbsp;IDT&nbsp; read only<br>; &nbsp;&nbsp;|-------------------------------|<br>; &nbsp;&nbsp;|&nbsp;0000 0400 - 0000 04FF&nbsp;&nbsp;|&nbsp;256B &nbsp;BIOS Data Area , read only&nbsp;<br>; &nbsp;&nbsp;|-------------------------------|<br>; &nbsp;&nbsp;|&nbsp;0000 0500 - 0000 7BFF&nbsp; &nbsp;|*&nbsp;30464B&nbsp;Free Memory , read/write &nbsp;(29.75KB) <br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;0000 7C00 - 0000 7DFF&nbsp;&nbsp; &nbsp;|&nbsp;512B&nbsp;Boot Sector , read/write&nbsp;<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;0000 7E00 - 0000 7FFF&nbsp;&nbsp;|&nbsp;512B&nbsp;&nbsp;&nbsp; Free Memory , read /write<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;0000 8000 - 0009 FBFF&nbsp; &nbsp;|&nbsp;607KB&nbsp;Free Memory , read / write( 32K - 639KB ) <br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>;
&nbsp;&nbsp;|&nbsp;0009 FC00 - 0009 FFFF&nbsp;&nbsp;
&nbsp;|**&nbsp;1KB&nbsp;&nbsp;EBDA extended BIOS data
area&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;000A 0000 - 000A FFFF&nbsp;&nbsp;|&nbsp;64KB&nbsp;Video Memory<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;000B 0000 - 000B 7FFF&nbsp; &nbsp;|&nbsp;32KB&nbsp;Mono Video Text Memory <br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;000B 8000 - 000B FFFF&nbsp;&nbsp; &nbsp;|&nbsp;32KB&nbsp;Color Video Text Memory<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;000C 0000 - 000C 7FFF&nbsp;&nbsp;|&nbsp;32KB&nbsp;Video BIOS , read only<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;000C 8000 - 000E FFFF&nbsp; &nbsp;|&nbsp;160KB&nbsp;Adapter ROM，read only<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;000F 0000 - 000F FFFF&nbsp;&nbsp; &nbsp;|&nbsp;64KB&nbsp;System BIOS, read only<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;0010 0000 - 0010 FFEF&nbsp;&nbsp;|***64KB-16&nbsp;High Memory Area,read/write&nbsp; ( 1MB開始處 )<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; &nbsp;&nbsp;|&nbsp;0010 FFF0 - &nbsp;&nbsp;&nbsp; &nbsp;|&nbsp;&nbsp;&nbsp;Free Extended Memory, read/write&nbsp;<br>; &nbsp;&nbsp;|------------------------------&nbsp;|<br>; <br>; &nbsp;*&nbsp;空閑內存實際并非從 0000 0500處開始，BIOS數據區實際上會利用從0000 0500開始的少量字節，例如<br>; &nbsp;&nbsp;00000500處保存的是打印屏幕狀態，當按下打印屏幕(PrintScreen)鍵時，低級鍵盤BIOS初始化打印屏<br>; &nbsp;&nbsp;幕功能，鍵盤BIOS觸發中斷5打印屏幕處理程序。正因為BIOS數據區越過了256B的界限，因此DOS實際<br>; &nbsp;&nbsp;上是從0000 0522開始裝載的。為保險起見，可從0000 0600開始利用空閑內存。（1.5K - 31K 29.5KB)<br>; <br>; **&nbsp;有些機器上沒有這段BIOS擴展數據區。<br>; <br>; ***&nbsp;如果沒有使用擴展高端內存區域程序（例如Emm386.exe)，則從0010 0000 (1MB )開始的內存都是可用的。<br>; <br>; <br>;=====================================================================================<br>; </p><p>BITS &nbsp;&nbsp;16&nbsp;&nbsp;&nbsp;; 生成16位代碼而不是32位代碼<br>SECTION&nbsp;&nbsp;.TEXT &nbsp;&nbsp;; 代碼段<br>ORG&nbsp;&nbsp;&nbsp;7C00H&nbsp;&nbsp;; 指定程序被裝入內存的起始位置</p><p>;====================================================================<br>; <br>; 宏和常量定義<br>; <br>;====================================================================<br>? &nbsp;&nbsp;&nbsp;&nbsp;EQU &nbsp;0&nbsp;&nbsp;; NASM不支持DW ?這樣的語法，可以使用這樣的定義<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 模擬，以使代碼的可讀性更強<br>DATA_BUF_SEG&nbsp;EQU&nbsp;&nbsp;0200H&nbsp;; 用于讀取根目錄或文件內容的緩沖區(8K) 段地址<br>DATA_BUF_OFF&nbsp;EQU&nbsp;&nbsp;2000H<br>STACK_ADDR&nbsp;&nbsp;EQU&nbsp;&nbsp;7BD0H&nbsp;; 堆棧棧頂(注意：堆棧大小約為20K)&nbsp;<br>OSLOADER_ADDR&nbsp;EQU&nbsp;&nbsp;8000H&nbsp;; FDOSLDR.BIN放入內存中的起始位置，這就意味著<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 裝載程序及相關資源的尺寸不能超過608K<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 8000H - A000H (32K - 640K )<br>OSLOADER_SEG&nbsp;EQU&nbsp;&nbsp;0800H&nbsp;; 起始段地址&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br>SECOND_SECTOR&nbsp;EQU&nbsp;&nbsp;03H&nbsp;&nbsp;; 第二個引導扇區的扇區號(第四個扇區)<br>SECOND_ADDR&nbsp;&nbsp;EQU&nbsp;&nbsp;7E00H&nbsp;; 第二個引導扇區的裝載位置</p><p>;====================================================================<br>; 用堆棧保存若干中間變量( SS = 0 BP = 7C00H )<br>;====================================================================<br>FAT_START_SECTOR&nbsp;EQU&nbsp;&nbsp;4&nbsp;&nbsp;; FAT表的起始扇區號&nbsp;&nbsp;DWORD<br>ROOT_START_SECTOR&nbsp;EQU&nbsp;&nbsp;8&nbsp;&nbsp;; 根目錄的起始扇區號&nbsp;DWORD<br>DATA_START_SECTOR&nbsp;EQU&nbsp;&nbsp;12&nbsp;&nbsp;; 數據區起始扇區號&nbsp;&nbsp;DWORD<br>FAT_ENTRY_SECTORS&nbsp;EQU&nbsp;&nbsp;14&nbsp;&nbsp;; FAT表所占的扇區數&nbsp;&nbsp;WORD<br>ROOT_ENTRY_SECTORS&nbsp;EQU&nbsp;&nbsp;16&nbsp;&nbsp;; 根目錄所占的扇區數&nbsp;WORD<br>DIR_PER_SECTOR&nbsp;&nbsp;EQU&nbsp;&nbsp;17&nbsp;&nbsp;; 每個扇區所容納的目錄&nbsp;BYTE<br>DISK_EXT_SUPPORT&nbsp;EQU&nbsp;&nbsp;18&nbsp;&nbsp;&nbsp;&nbsp; ; 磁盤是否支持擴展BIOS&nbsp;BYTE<br>CURRENT_CLUSTER&nbsp;&nbsp;EQU&nbsp;&nbsp;40&nbsp;&nbsp;; 當前正在處理的簇號&nbsp;DWORD</p><p><br>;====================================================================&nbsp;&nbsp;<br>; 擴展磁盤服務所使用的地址包<br>;====================================================================<br>DAP_SECTOR_HIGH&nbsp;&nbsp;EQU&nbsp;&nbsp;24&nbsp;&nbsp;; 起始扇區號的高32位 ( 每次調用需要重置 )&nbsp;DWORD<br>DAP_SECTOR_LOW&nbsp;&nbsp;EQU&nbsp;&nbsp;28&nbsp;&nbsp;; 起始扇區號的低32位 ( 每次調用需要重置 )&nbsp;DWORD<br>DAP_BUFFER_SEG&nbsp;&nbsp;EQU&nbsp;&nbsp;30&nbsp;&nbsp;; 緩沖區段地址&nbsp;&nbsp; ( 每次調用需要重置 )&nbsp;WORD<br>DAP_BUFFER_OFF&nbsp;&nbsp;EQU&nbsp;&nbsp;32&nbsp;&nbsp;; 緩沖區偏移&nbsp;&nbsp; ( 每次調用需要重置 )&nbsp;WORD&nbsp;&nbsp;<br>DAP_RESERVED2&nbsp;&nbsp;EQU&nbsp;&nbsp;33&nbsp;&nbsp;; 保留字節<br>DAP_READ_SECTORS&nbsp;EQU&nbsp;&nbsp;34&nbsp;&nbsp;; 要處理的扇區數(1 - 127 )<br>DAP_RESERVED1&nbsp;&nbsp;EQU&nbsp;&nbsp;35&nbsp;&nbsp;; 保留字節<br>DAP_PACKET_SIZE&nbsp;&nbsp;EQU&nbsp;&nbsp;36&nbsp;&nbsp;; 包的大小為16字節</p><p>;====================================================================<br>; <br>; 目錄項結構(每個結構為32字節)<br>; <br>;====================================================================<br>OFF_DIR_NAME&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;0&nbsp;&nbsp;; 目錄項的偏移&nbsp;&nbsp;BYTE[11]<br>OFF_DIR_ATTRIBUTE&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;11&nbsp;&nbsp;; 目錄屬性&nbsp;&nbsp;&nbsp;BYTE<br>OFF_NT_RESERVED&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;12&nbsp;&nbsp;; 保留屬性&nbsp;&nbsp;&nbsp;BYTE<br>OFF_CREATE_TIME_HUNDREDTH&nbsp;EQU&nbsp;&nbsp;13&nbsp;&nbsp;; 創建時間&nbsp;&nbsp;&nbsp;BYTE<br>OFF_CREATE_TIME&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;14&nbsp;&nbsp;; 創建時間&nbsp;&nbsp;&nbsp;WORD<br>OFF_CREATE_DATE&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;16&nbsp;&nbsp;; 創建時間&nbsp;&nbsp;&nbsp;WORD<br>OFF_LAST_ACCESS_DATE&nbsp;&nbsp;EQU&nbsp;&nbsp;18&nbsp;&nbsp;; 上次訪問時間&nbsp;&nbsp;WORD<br>OFF_START_CLUSTER_HIGH&nbsp;&nbsp;EQU&nbsp;&nbsp;20&nbsp;&nbsp;; 起始簇號高位&nbsp;&nbsp;WORD<br>OFF_LAST_UPDATE_TIME&nbsp;&nbsp;EQU&nbsp;&nbsp;22&nbsp;&nbsp;; 上次更新時間&nbsp;&nbsp;WORD<br>OFF_LAST_UPDATE_DATE&nbsp;&nbsp;EQU&nbsp;&nbsp;24&nbsp;&nbsp;; 上次更新時間&nbsp;&nbsp;WORD<br>OFF_START_CLUSTER_LOW&nbsp;&nbsp;EQU&nbsp;&nbsp;26&nbsp;&nbsp;; 起始簇號低位&nbsp;&nbsp;WORD<br>OFF_FILE_SIZE&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;28&nbsp;&nbsp;; 文件尺寸&nbsp;&nbsp;&nbsp;DWORD</p><p>; 相關常量<br>DIR_NAME_DELETED&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;0E5H&nbsp;; 該項已經被刪除<br>DIR_NAME_FREE&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;00H&nbsp;&nbsp;; 該項是空閑的(其后也是空閑的)<br>DIR_NAME_DOT&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;2EH&nbsp;&nbsp;; 特殊目錄 . 或 ..<br>DIR_NAME_SPACE&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;20H&nbsp;&nbsp;; 不允許的字符<br>DIR_ENTRY_SIZE&nbsp;&nbsp;&nbsp;&nbsp;EQU &nbsp;32&nbsp;&nbsp;; 每個目錄項的尺寸，其結構如上所示&nbsp;</p><p>;文件屬性<br>DIR_ATTR_READONLY&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;01H&nbsp;&nbsp;; 只讀文件<br>DIR_ATTR_HIDDEN&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;02H&nbsp;&nbsp;; 隱藏文件<br>DIR_ATTR_SYSTEM&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;04H&nbsp;&nbsp;; 系統文件<br>DIR_ATTR_VOLUME&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;08H&nbsp;&nbsp;; 卷標號(只可能出現在根目錄中)<br>DIR_ATTR_SUBDIR&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;10H&nbsp;&nbsp;; 子目錄<br>DIR_ATTR_ARCHIVE&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;20H&nbsp;&nbsp;; 歸檔屬性<br>DIR_ATTR_LONGNAME&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;0FH&nbsp;&nbsp;; 長文件名<br>DIR_ATTR_LONGNAME_MASK&nbsp;&nbsp;EQU&nbsp;&nbsp;3FH&nbsp;&nbsp;; 長文件名掩碼</p><p>; 簇屬性<br>CLUSTER_MASK&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;0FFFFFFFH&nbsp;; 簇號掩碼(FAT32=&gt;FAT28)<br>CLUSTER_FREE&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;00000000H&nbsp;; 簇是空閑的<br>CLUSTER_RESERVED&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;00000001H&nbsp;; 簇是保留的<br>CLUSTER_MIN_VALID&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;00000002H&nbsp;; 最小有效簇號<br>CLUSTER_MAX_VALID&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;0FFFFFF6H&nbsp;; 最大有效簇號<br>CLUSTER_BAD&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;0FFFFFF7H&nbsp;; 壞簇<br>CLUSTER_LAST&nbsp;&nbsp;&nbsp;&nbsp;EQU&nbsp;&nbsp;0FFFFFF8H&nbsp;&nbsp; ;0xFFFFFFF8-0xFFFFFFFF表示文件的最后一個簇</p><p>;====================================================================<br>;<br>; 啟動扇區(512字節)<br>;<br>;====================================================================<br>_ENTRY_POINT: </p><p>; 3字節的跳轉指令<br>&nbsp;JMP&nbsp;SHORT _BOOT_CODE&nbsp;; 跳轉到真正的引導代碼<br>&nbsp;NOP&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 空指令以保證字節數為3</p><p>; 8字節的OEMName<br>OEMName&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;DB&nbsp;"FDOS1.00"</p><p>;====================================================================<br>; <br>; BPB( BIOS Parameter Block ) <br>; <br>;====================================================================<br>BytesPerSector&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;; 每個扇區的字節數 (512 1024 2048 4096)<br>SectorsPerCluster&nbsp;&nbsp;DB&nbsp;?&nbsp;; 每個簇的扇區數 ( 1 2 4 8 16 32 64 128 )<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 兩者相乘不能超過32K(簇最大大小)<br>ReservedSectors&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;; 從卷的第一個扇區開始的保留扇區數目；<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 該值不能為0，對于FAT12/FAT16，該值通常為1；<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 對于FAT32，典型值為32；<br>NumberOfFATs&nbsp;&nbsp;&nbsp;DB&nbsp;?&nbsp;; 卷上FAT數據結構的數目，該值通常應為2<br>RootEntries&nbsp;&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;; 對于FAT12/FAT16,該值表示32字節目錄項的數目；<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 對于FAT32，該值必須為0；<br>NumberOfSectors16&nbsp;&nbsp;DW&nbsp;?&nbsp;; 該卷上的扇區總數，該字段可以為0，如果該字段<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 為0，則NumberOfSectors32不能為0；對于FAT32，<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 該字段必須為0<br>MediaDescriptor&nbsp;&nbsp;&nbsp;DB&nbsp;?&nbsp;; 介質類型<br>SectorsPerFAT16&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;; 該字段標識一個FAT結構占有的扇區數（FAT12/FAT16），<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 對于FAT32卷，該字段必須為0；<br>SectorsPerTrack&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;; 用于INT 0x13中斷的每個磁道的扇區數<br>HeadsPerCylinder&nbsp;&nbsp;DW&nbsp;?&nbsp;; 用于INT 0x13中斷的每個柱面的磁頭數<br>HiddenSectors&nbsp;&nbsp;&nbsp;DD&nbsp;?&nbsp;; 包含該FAT卷的分區之前的隱藏扇區數<br>NumberOfSectors32&nbsp;&nbsp;DD&nbsp;?&nbsp;; 該字段包含該卷上的所有扇區數目，對于FAT32，該字段<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 不為0；FAT12/FAT16可根據實際大小是否超過65536個扇<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 區數決定是否采用該字段；</p><p>;====================================================================<br>; <br>; EBPB ( Extended BIOS Parameter Block )<br>; <br>;====================================================================<br>SectorsPerFAT32&nbsp;&nbsp;&nbsp;DD&nbsp;?&nbsp;&nbsp;&nbsp;; 對于FAT32，該字段包含一個FAT的大小，而SectorsPerFAT16<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 字段必須為0;<br>ExtFlags&nbsp;&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;&nbsp;&nbsp;; 標志&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br>FSVersion&nbsp;&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;&nbsp;&nbsp;; 這是文件系統的版本，高字節為主版本，低字節為次版本；<br>RootDirectoryStart&nbsp;&nbsp;DD&nbsp;?&nbsp;&nbsp;&nbsp;; 根目錄的起始簇號，通常為2；<br>FSInfoSector&nbsp;&nbsp;&nbsp;DW&nbsp;?&nbsp;&nbsp;&nbsp;; FSINFO結構在FAT32卷保留區域的扇區號 <br>BackupBootSector&nbsp;&nbsp;DW&nbsp;?&nbsp;&nbsp;&nbsp;; 如果該字段不為0，則表示在保留區域保存的啟動記錄的扇區號<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 通常為6，不推薦其他值；<br>Reserved1&nbsp;TIMES 12&nbsp;DB&nbsp;?&nbsp;&nbsp;&nbsp;; 保留字段，格式化程序應將該字段清0<br>DriveNumber&nbsp;&nbsp;&nbsp;&nbsp;DB&nbsp;?&nbsp;&nbsp;&nbsp;; 用于INT 0x13的驅動器號，0x00為軟盤，0x80為硬盤<br>NTReserved&nbsp;&nbsp;&nbsp;&nbsp;DB&nbsp;?&nbsp;&nbsp;&nbsp;; 保留字節（用于Windows NT，即NTFS），對于FAT文件<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 系統，應始終為0<br>BootSignature&nbsp;&nbsp;&nbsp;DB &nbsp;29H&nbsp;&nbsp;&nbsp;; 擴展引導標志（值為0x29）<br>VolumeId&nbsp;&nbsp;&nbsp;&nbsp;DD&nbsp;?&nbsp;&nbsp;&nbsp;; 卷的序列號<br>VolumeLabel&nbsp; times 11&nbsp;&nbsp; DB&nbsp;?&nbsp;&nbsp;&nbsp;; 卷標號，該字段與根目錄中的11字節卷標相同<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; NASM目前尚不支持DUP語法<br>FileSystemType&nbsp;&nbsp;&nbsp;DB&nbsp;'FAT32&nbsp;&nbsp; '&nbsp;; 文件系統類型</p><p>;====================================================================<br>;<br>; 真正的啟動代碼從這開始( 偏移：0x3E )&nbsp;<br>; 其功能是搜索磁盤的根目錄，查找FDOSLDR.BIN文件，將其讀入內存并運行。<br>;<br>;====================================================================<br>_BOOT_CODE:</p><p>&nbsp;; 初始化相關寄存器及標志位<br>&nbsp;CLI&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 先關掉中斷<br>&nbsp;CLD&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 方向為向前遞增<br>&nbsp;XOR&nbsp;&nbsp;AX,AX&nbsp;&nbsp;&nbsp;; AX = 0<br>&nbsp;MOV &nbsp;DS,AX&nbsp;&nbsp;&nbsp;; 設置數據段寄存器&nbsp;DS:SI<br>&nbsp;MOV&nbsp;&nbsp;ES,AX&nbsp;&nbsp;&nbsp;; 設置附加段寄存器&nbsp;ES:DI<br>&nbsp;MOV&nbsp;&nbsp;SS,AX&nbsp;&nbsp;&nbsp;; 設置堆棧段寄存器<br>&nbsp;MOV&nbsp;&nbsp;BP,7C00H&nbsp;&nbsp;; 設置基址寄存器<br>&nbsp;MOV&nbsp;&nbsp;SP,STACK_ADDR&nbsp;; 設置堆棧棧頂<br>&nbsp;STI&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 允許中斷</p><p>&nbsp;;====================================================================<br>&nbsp;; 保存啟動的磁盤編號<br>&nbsp;;====================================================================<br>&nbsp;MOV &nbsp;[DriveNumber],DL; 該值由BIOS設置，如果是從USB啟動，該值為0x80<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 即為第一個硬盤的編號，該值將用于后續的磁盤<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 讀取調用</p><p><br>&nbsp;;====================================================================&nbsp;&nbsp;<br>&nbsp;; 準備FAT32文件系統常用的常數，以便后面的操作<br>&nbsp;;====================================================================<br>&nbsp;;<br>&nbsp;; [隱藏扇區][保留扇區][FAT][DATA]<br>&nbsp;;<br>&nbsp;;====================================================================<br>&nbsp;<br>&nbsp;;====================================================================&nbsp;&nbsp;<br>&nbsp;; 檢查是否支持磁盤中斷INT 13H的擴展<br>&nbsp;;====================================================================<br>&nbsp;MOV&nbsp;&nbsp;BYTE [BP - DISK_EXT_SUPPORT],00H&nbsp;&nbsp;; 00H表示不支持磁盤擴展<br>&nbsp;MOV&nbsp;&nbsp;DL,[DriveNumber]<br>&nbsp;MOV&nbsp;&nbsp;AH,41H<br>&nbsp;MOV &nbsp;BX,055AAH<br>&nbsp;INT&nbsp;&nbsp;13H<br>&nbsp;JC&nbsp;&nbsp;_NO_DISK_EXTENSION&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 如果失敗，進位標志為1或者BX值不對( AA55 or 55AA )<br>&nbsp;<br>&nbsp;; 設置磁盤支持擴展中斷標志<br>&nbsp;MOV&nbsp;&nbsp;BYTE [BP - DISK_EXT_SUPPORT],01H&nbsp;&nbsp;; 01H表示支持磁盤擴展</p><p>; 不支持磁盤擴展<br>_NO_DISK_EXTENSION:<br>&nbsp;<br>&nbsp;; 檢查是否為FAT32分區<br>&nbsp;; 對于FAT32分區，其根目錄項為0<br>&nbsp;CMP&nbsp;&nbsp;WORD [RootEntries],0<br>&nbsp;JNZ&nbsp;&nbsp;NEAR _DISK_ERROR<br>&nbsp;<br>&nbsp;; 檢查保留扇區數(保留扇區必須大于等于4，我們將<br>&nbsp;; 第二個扇區的代碼存在第四個扇區)<br>&nbsp;CMP&nbsp;&nbsp;WORD [ReservedSectors],4<br>&nbsp;JB&nbsp;&nbsp;NEAR _DISK_ERROR <br>&nbsp;<br>&nbsp;; 檢查每FAT扇區數<br>&nbsp;; SectorsPerFAT16 == 0<br>&nbsp;; SectorsPerFAT32 != 0<br>&nbsp;CMP&nbsp;&nbsp;WORD [SectorsPerFAT16],0<br>&nbsp;JNZ&nbsp;&nbsp;NEAR _DISK_ERROR<br>&nbsp;CMP&nbsp;&nbsp;DWORD[SectorsPerFAT32],0<br>&nbsp;JZ&nbsp;&nbsp;NEAR _DISK_ERROR<br>&nbsp;<br>&nbsp;; 計算每個扇區包含的目錄項 ( 512/32 = 16 = 10H )<br>&nbsp;MOV&nbsp;&nbsp;AX,WORD [BytesPerSector]<br>&nbsp;MOV&nbsp;&nbsp;CL,DIR_ENTRY_SIZE<br>&nbsp;DIV&nbsp;&nbsp;CL&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; AH:AL = BytesPerSector / 32 ( AH = Remainder = 0 )<br>&nbsp;MOV&nbsp;&nbsp;BYTE [BP - DIR_PER_SECTOR],AL&nbsp;; AL&nbsp;&nbsp;&nbsp; = DirEntriesPerSector<br>&nbsp;<br>&nbsp;; FAT起始扇區<br>&nbsp;; FAT起始扇區 = Hidden+Reserved<br>&nbsp;MOV &nbsp;AX ,WORD [ReservedSectors]<br>&nbsp;CWD&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; AX =&gt; DX : AX<br>&nbsp;ADD &nbsp;AX, WORD [HiddenSectors]<br>&nbsp;ADC&nbsp; &nbsp;DX, WORD [HiddenSectors+2]&nbsp;&nbsp;<br>&nbsp;MOV &nbsp;WORD[ BP - FAT_START_SECTOR&nbsp; ],AX <br>&nbsp;MOV&nbsp; &nbsp;WORD[ BP - FAT_START_SECTOR+2],DX <br>&nbsp;<br>&nbsp;<br>&nbsp;; FAT表所占的扇區數<br>&nbsp;; FAT_SECTORS = NumberOfFAT * SectorsPerFAT<br>&nbsp;XOR&nbsp;&nbsp;EAX,EAX<br>&nbsp;MOV&nbsp;&nbsp;AL, BYTE [NumberOfFATs]&nbsp;&nbsp;; FAT的數目<br>&nbsp;MOV&nbsp;&nbsp;EBX,DWORD [SectorsPerFAT32]<br>&nbsp;MUL&nbsp;&nbsp;EBX &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 乘積放入 EDX:EAX<br>&nbsp;MOV &nbsp;DWORD [ BP - FAT_ENTRY_SECTORS &nbsp;] , EAX<br>&nbsp;<br>&nbsp;; 計算數據區起始扇區<br>&nbsp;ADD &nbsp;EAX ,DWORD[ BP - FAT_START_SECTOR&nbsp; ]<br>&nbsp;MOV &nbsp;DWORD [ BP - DATA_START_SECTOR&nbsp;],EAX <br>&nbsp;<br>&nbsp;<br>&nbsp;;====================================================================<br>&nbsp;;<br>&nbsp;; 初始化DiskAddressPacket<br>&nbsp;; 使用時只需要修改字段：DATA_BUFFER_OFF DATA_BUFFER_SEG <br>&nbsp;; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;DAP_SECTOR_LOW &nbsp;DAP_SECTOR_HIGH<br>&nbsp;;<br>&nbsp;;====================================================================<br>&nbsp;MOV &nbsp;DWORD [BP - DAP_SECTOR_HIGH ],00H<br>&nbsp;MOV &nbsp;BYTE&nbsp; [BP - DAP_RESERVED1&nbsp;&nbsp; ],00H<br>&nbsp;MOV &nbsp;BYTE&nbsp; [BP - DAP_RESERVED2&nbsp;&nbsp; ],00H<br>&nbsp;MOV &nbsp;BYTE&nbsp; [BP - DAP_PACKET_SIZE ],10H<br>&nbsp;MOV &nbsp;BYTE&nbsp; [BP - DAP_READ_SECTORS],01H<br>&nbsp;MOV &nbsp;WORD&nbsp; [BP - DAP_BUFFER_SEG&nbsp; ],00H<br>&nbsp;MOV &nbsp;BYTE&nbsp; [BP - DAP_READ_SECTORS],01H&nbsp;&nbsp;; 每次只讀取一個扇區<br>&nbsp;<br>&nbsp;; 裝載第二個啟動扇區&nbsp;<br>&nbsp;MOV &nbsp;WORD&nbsp; [BP - DAP_BUFFER_OFF&nbsp; ],SECOND_ADDR&nbsp;<br>&nbsp;MOV&nbsp;&nbsp;EAX , DWORD[HiddenSectors]<br>&nbsp;ADD&nbsp;&nbsp;EAX , SECOND_SECTOR<br>&nbsp;MOV&nbsp;&nbsp;DWORD [BP - DAP_SECTOR_LOW&nbsp; ],EAX<br>&nbsp;CALL&nbsp;ReadSector<br>&nbsp;<br>&nbsp;<br>&nbsp;; 下面開始查找根目錄并且裝載FDOSLDR.BIN<br>&nbsp;JMP&nbsp;&nbsp;_SEARCH_LOADER<br>&nbsp;<br>;====================================================================<br>;&nbsp;錯誤處理<br>;====================================================================<br>_MISSING_LOADER:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 顯示沒有裝載程序<br>&nbsp;MOV&nbsp;&nbsp;SI,MessageMissLoader<br>&nbsp;CALL&nbsp;ShowMessage<br>&nbsp;JMP&nbsp;&nbsp;_REBOOT</p><p>_DISK_ERROR:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 顯示磁盤錯誤信息<br>&nbsp;MOV&nbsp;&nbsp;SI,MessageDiskError<br>&nbsp;CALL&nbsp;ShowMessage</p><p>_REBOOT:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 重啟<br>&nbsp;MOV&nbsp;&nbsp;SI,MessageRestart<br>&nbsp;CALL&nbsp;ShowMessage<br>&nbsp;<br>&nbsp;; 調用鍵盤中斷，等待用戶按鍵<br>&nbsp;MOV&nbsp;&nbsp;AH,00H<br>&nbsp;INT&nbsp;&nbsp;16H<br>&nbsp;<br>&nbsp;; 重啟計算機<br>&nbsp;INT&nbsp;&nbsp;19H&nbsp;</p><p>&nbsp;; 死循環<br>&nbsp;JMP &nbsp;$</p><p><br>;====================================================================<br>; <br>; 子過程<br>; <br>;====================================================================</p><p>;====================================================================<br>; <br>; 讀取一個磁盤扇區<br>;&nbsp;輸入： 已經設置了DAP中相應的字段<br>;&nbsp;限制： 不能讀取超過一個簇的內容&nbsp;&nbsp;&nbsp;<br>; <br>;====================================================================<br>ReadSector:</p><p>&nbsp;PUSHA&nbsp;&nbsp;; 保存寄存器<br>&nbsp;<br>&nbsp;; 檢查是否使用擴展方式<br>&nbsp;CMP&nbsp;&nbsp;BYTE [BP - DISK_EXT_SUPPORT],00H<br>&nbsp;JZ&nbsp;&nbsp;.NoDiskExtension<br>&nbsp;<br>;====================================================================<br>; INT 13H &nbsp;AH = 42H 擴展磁盤調用<br>;====================================================================<br>&nbsp;; 每次讀取一個扇區<br>&nbsp;MOV&nbsp;&nbsp;AH,42H&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 功能號&nbsp;<br>&nbsp;LEA &nbsp;SI ,[BP - DAP_PACKET_SIZE]&nbsp;&nbsp;&nbsp;&nbsp;; 地址包地址</p><p>&nbsp;; 驅動器號<br>&nbsp;MOV &nbsp;DL ,[DriveNumber]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 驅動器號<br>&nbsp;INT &nbsp;13H<br>&nbsp;JC &nbsp;&nbsp;_DISK_ERROR&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 讀取失敗<br>&nbsp;JMP&nbsp;&nbsp;_READ_SECTOR_OK&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 讀取成功</p><p>;====================================================================<br>;&nbsp;<br>; INT 13H&nbsp;<br>;&nbsp;&nbsp;AH = 2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;柱面號：0 - 1023<br>;&nbsp;&nbsp;AL = 要讀取的扇區數&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;磁頭號：0 - 255&nbsp;&nbsp;&nbsp; <br>;&nbsp;&nbsp;CH = 柱面號低8位&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;扇區號：1 - 63&nbsp; <br>;&nbsp;&nbsp;CL = 柱面號高2位 : 6位扇區號&nbsp;&nbsp;<br>;&nbsp;&nbsp;DH = 磁頭號 <br>;&nbsp;&nbsp;DL = 驅動器號<br>;<br>;&nbsp;LBA = ( (cylinder * HeadsPerCylinder + heads ) * SectorsPerTrack ) + sector - 1<br>;<br>;&nbsp;Sector&nbsp;= LBA % SectorsPerTrack +1<br>;&nbsp;Head&nbsp;= (&nbsp; LBA / SectorsPerTrack&nbsp;) % HeadsPerCylinder<br>;&nbsp;&nbsp; Cylinder= (&nbsp; LBA / SectorsPerTrack&nbsp;) / HeadsPerCylinder<br>;<br>;====================================================================&nbsp;<br>.NoDiskExtension:<br>&nbsp;&nbsp;<br>&nbsp;;====================================================================&nbsp;&nbsp;<br>&nbsp;; 首先需要將扇區號轉換為CHS地址<br>&nbsp;;====================================================================<br>&nbsp;<br>&nbsp;; 首先計算扇區號<br>&nbsp;MOV&nbsp;&nbsp;AX,WORD [ BP - DAP_SECTOR_LOW&nbsp;&nbsp; ]<br>&nbsp;MOV&nbsp;&nbsp;DX,WORD&nbsp;[ BP - DAP_SECTOR_LOW+2 ]<br>&nbsp;DIV&nbsp;&nbsp;WORD [SectorsPerTrack ] ; AX = LBA / SectorsPerTrack DX = LDA % SectorsPerTrack<br>&nbsp;MOV&nbsp;&nbsp;CX,DX<br>&nbsp;INC&nbsp;&nbsp;CX&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; CL = Sector<br>&nbsp;AND&nbsp;&nbsp;CL,3FH&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 1-63</p><p>&nbsp;; 再計算磁頭號和柱面號<br>&nbsp;XOR&nbsp;&nbsp;DX,DX&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; DX:AX = LBA / SectorsPerTrack<br>&nbsp;DIV&nbsp;&nbsp;WORD [HeadsPerCylinder] ; DX = ( LBA/SectorsPerTrack ) %&nbsp; HeadsPerCylinder = Head<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; AX = ( LBA/SectorsPerTrack ) /&nbsp; HeadsPerCylinder = Cylinder<br>&nbsp;MOV&nbsp;&nbsp;CH,AL&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 柱面號低8位<br>&nbsp;SHL&nbsp;&nbsp;AH,6<br>&nbsp;OR&nbsp;&nbsp;CL,AH&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; CL = 柱面號高2位：6位扇區號<br>&nbsp;MOV&nbsp;&nbsp;DH,DL&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; DL = 磁頭號<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br>&nbsp;; 準備讀取磁盤&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br>&nbsp;MOV&nbsp;&nbsp;AX,WORD[ BP - DAP_BUFFER_SEG ]<br>&nbsp;MOV&nbsp;&nbsp;ES,AX<br>&nbsp;MOV&nbsp;&nbsp;BX,WORD[ BP - DAP_BUFFER_OFF ]<br>&nbsp;MOV&nbsp;&nbsp;AX ,0201H&nbsp;&nbsp;&nbsp;&nbsp;; 每次只讀取一個扇區<br>&nbsp;<br>&nbsp;; 驅動器號<br>&nbsp;MOV &nbsp;DL ,[DriveNumber]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 驅動器號<br>&nbsp;INT &nbsp;13H<br>&nbsp;JC &nbsp;&nbsp;_DISK_ERROR&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 讀取失敗</p><p>_READ_SECTOR_OK:<br>&nbsp;POPA&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 恢復寄存器&nbsp;<br>&nbsp;RET <br>&nbsp;&nbsp;&nbsp; <br>;====================================================================<br>; <br>; 顯示一個字符串<br>;&nbsp;輸入：<br>;&nbsp;&nbsp;&nbsp;DS:SI &nbsp;= 字符串的起始地址(以NULL結束)<br>;&nbsp;&nbsp;&nbsp;<br>;====================================================================<br>ShowMessage:<br>&nbsp;LODSB&nbsp;&nbsp;&nbsp;&nbsp;; AL = DS:[SI] SI = SI+1<br>&nbsp;OR&nbsp;&nbsp;AL,AL&nbsp;&nbsp; &nbsp;; 檢測是否遇到NULL字符串<br>&nbsp;JZ&nbsp;&nbsp;_SHOW_END<br>&nbsp;MOV&nbsp;&nbsp;AH,0EH<br>&nbsp;MOV&nbsp;&nbsp;BX,07H<br>&nbsp;INT&nbsp;&nbsp;10H<br>&nbsp;JMP&nbsp;&nbsp;ShowMessage</p><p>_SHOW_END:<br>&nbsp;RET&nbsp;</p><p>;====================================================================<br>; 數據區<br>;====================================================================<br>LoaderName&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;db&nbsp;"FDOSLDR BIN"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 第二階段啟動程序 FDOSLDR.BIN<br>MessageMissLoader&nbsp;&nbsp;&nbsp;db&nbsp;"NO FDOSLDR.BIN.",0DH,0AH,00H&nbsp;&nbsp;&nbsp;; 沒有找到裝載程序<br>MessageDiskError&nbsp;&nbsp;&nbsp;db &nbsp;"Disk Error.",0DH,0AH,00&nbsp;&nbsp;&nbsp;&nbsp;; 磁盤錯誤消息<br>MessageRestart&nbsp;&nbsp;&nbsp;&nbsp;db&nbsp;"Press any key to restart." ,0DH,0AH,00&nbsp;; 提示重啟消息</p><p>;====================================================================<br>; 扇區最后的標記字節(NASM不支持重復ORG)<br>;====================================================================<br>Padding&nbsp;TIMES 510-($-$$)&nbsp;db &nbsp;00H<br>SectorSignature&nbsp;&nbsp;&nbsp;&nbsp;dw&nbsp;0AA55H</p><p></p><p>;====================================================================<br>; 第二個扇區的代碼(該代碼位于分區的第四個扇區)<br>;====================================================================</p><p>;====================================================================<br>; 查找根目錄，檢查是否有 FDOSLDR.BIN文件<br>;====================================================================<br>_SEARCH_LOADER:&nbsp;</p><p><br>&nbsp;; 設置緩沖區<br>&nbsp;MOV&nbsp;&nbsp;WORD [ BP - DAP_BUFFER_OFF&nbsp; ], DATA_BUF_OFF&nbsp;; 0000:1000H<br>&nbsp;<br>&nbsp;; 根目錄起始扇區號<br>&nbsp;MOV&nbsp;&nbsp;EAX,DWORD[RootDirectoryStart]<br>&nbsp;MOV&nbsp;&nbsp;DWORD[ BP - CURRENT_CLUSTER ],EAX</p><p>; 檢查下一個簇<br>_NEXT_ROOT_CLUSTER: </p><p>&nbsp;; 根據簇號計算扇區號<br>&nbsp;DEC&nbsp;&nbsp;EAX<br>&nbsp;DEC&nbsp;&nbsp;EAX&nbsp;&nbsp;; EAX = EAX - 2<br>&nbsp;XOR&nbsp;&nbsp;EBX,EBX&nbsp;<br>&nbsp;MOV&nbsp;&nbsp;BL, BYTE[ SectorsPerCluster]<br>&nbsp;MUL&nbsp;&nbsp;EBX&nbsp;<br>&nbsp;ADD&nbsp;&nbsp;EAX,DWORD[ BP- DATA_START_SECTOR]<br>&nbsp;MOV&nbsp;&nbsp;DWORD[ BP - DAP_SECTOR_LOW &nbsp;], EAX<br>&nbsp;MOV&nbsp;&nbsp;DL,[SectorsPerCluster]</p><p>; 檢查下一個扇區<br>_NEXT_ROOT_SECTOR:<br>&nbsp;&nbsp;<br>&nbsp;; 依次讀取每個根目錄扇區，檢查是否存在FDOSLDR.BIN文件<br>&nbsp;CALL&nbsp;ReadSector<br>&nbsp;<br>&nbsp;; 檢查該扇區內容<br>&nbsp;MOV&nbsp;&nbsp;DI,DATA_BUF_OFF<br>&nbsp;MOV &nbsp;BL,BYTE [ BP - DIR_PER_SECTOR]</p><p>; 檢查每一個目錄項<br>_NEXT_ROOT_ENTRY:<br>&nbsp;CMP &nbsp;BYTE [DI],DIR_NAME_FREE<br>&nbsp;JZ&nbsp;&nbsp;_MISSING_LOADER&nbsp;&nbsp;&nbsp; ; NO MORE DIR ENTRY<br>&nbsp;<br>&nbsp;; 檢查是否裝載程序<br>&nbsp;PUSH &nbsp;DI&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ; 保存DI<br>&nbsp;MOV &nbsp;SI,LoaderName<br>&nbsp;MOV &nbsp;CX,11<br>&nbsp;REPE &nbsp;CMPSB <br>&nbsp;JCXZ &nbsp;_FOUND_LOADER&nbsp;&nbsp;&nbsp; ; 裝載Loader并運行<br>&nbsp;&nbsp;<br>&nbsp;; 是否還有下一個目錄項(內層循環)<br>&nbsp;POP&nbsp;&nbsp;DI<br>&nbsp;ADD&nbsp; &nbsp;DI,DIR_ENTRY_SIZE<br>&nbsp;DEC &nbsp;BL <br>&nbsp;JNZ&nbsp; &nbsp;_NEXT_ROOT_ENTRY<br>&nbsp;<br>&nbsp;; 檢查是否還有下一個扇區可讀(外層循環)<br>&nbsp;DEC &nbsp;DL<br>&nbsp;JZ&nbsp;&nbsp;_CHECK_NEXT_ROOT_CLUSTER<br>&nbsp;INC&nbsp;&nbsp;DWORD [ BP - DAP_SECTOR_LOW ]&nbsp;; 增加扇區號<br>&nbsp;JMP&nbsp;&nbsp;_NEXT_ROOT_SECTOR&nbsp;<br>&nbsp;<br>; 檢查下一個簇<br>_CHECK_NEXT_ROOT_CLUSTER:</p><p>&nbsp;; 計算FAT所在的簇號和偏移 <br>&nbsp;; FatOffset = ClusterNum*4<br>&nbsp;XOR&nbsp;&nbsp;EDX,EDX<br>&nbsp;MOV&nbsp;&nbsp;EAX,DWORD[BP - CURRENT_CLUSTER]<br>&nbsp;SHL&nbsp;&nbsp;EAX,2<br>&nbsp;XOR&nbsp;&nbsp;ECX,ECX<br>&nbsp;MOV&nbsp;&nbsp;CX,WORD [ BytesPerSector ]<br>&nbsp;DIV&nbsp;&nbsp;ECX&nbsp;&nbsp;; EAX = Sector EDX = OFFSET<br>&nbsp;ADD&nbsp;&nbsp;EAX,DWORD [BP - FAT_START_SECTOR&nbsp; ]<br>&nbsp;MOV&nbsp;&nbsp;DWORD [ BP - DAP_SECTOR_LOW ], EAX <br>&nbsp;&nbsp;&nbsp;<br>&nbsp;; 讀取扇區<br>&nbsp;CALL &nbsp;ReadSector<br>&nbsp;&nbsp;<br>&nbsp;; 檢查下一個簇<br>&nbsp;MOV&nbsp;&nbsp;DI,DX<br>&nbsp;ADD&nbsp;&nbsp;DI,DATA_BUF_OFF<br>&nbsp;MOV&nbsp;&nbsp;EAX,DWORD[DI]&nbsp;&nbsp;; EAX = 下一個要讀的簇號<br>&nbsp;AND&nbsp;&nbsp;EAX,CLUSTER_MASK<br>&nbsp;MOV&nbsp;&nbsp;DWORD[ BP - CURRENT_CLUSTER ],EAX<br>&nbsp;CMP&nbsp;&nbsp;EAX,CLUSTER_LAST&nbsp;&nbsp;; CX &gt;= 0FFFFFF8H，則意味著沒有更多的簇了<br>&nbsp;JB&nbsp;&nbsp;_NEXT_ROOT_CLUSTER<br>&nbsp;JMP&nbsp;&nbsp;_MISSING_LOADER</p><p>;====================================================================<br>;&nbsp;裝載FDOSLDR.BIN文件<br>;====================================================================<br>_FOUND_LOADER:<br>&nbsp;; 目錄結構地址放在DI中<br>&nbsp;POP&nbsp;&nbsp;DI<br>&nbsp;XOR&nbsp;&nbsp;EAX,EAX<br>&nbsp;MOV&nbsp;&nbsp;AX,[DI+OFF_START_CLUSTER_HIGH] ; 起始簇號高32位<br>&nbsp;SHL&nbsp;&nbsp;AX,16<br>&nbsp;MOV&nbsp;&nbsp;AX,[DI+OFF_START_CLUSTER_LOW]&nbsp; ; 起始簇號低32位<br>&nbsp;MOV&nbsp;&nbsp;DWORD[ BP - CURRENT_CLUSTER ],EAX<br>&nbsp;MOV&nbsp;&nbsp;CX, OSLOADER_SEG&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ; CX&nbsp; = 緩沖區段地址&nbsp;<br>&nbsp;<br>&nbsp;&nbsp;<br>_NEXT_DATA_CLUSTER:<br>&nbsp;<br>&nbsp;; 根據簇號計算扇區號<br>&nbsp;DEC&nbsp;&nbsp;EAX<br>&nbsp;DEC&nbsp;&nbsp;EAX&nbsp;&nbsp;; EAX = EAX - 2<br>&nbsp;XOR&nbsp;&nbsp;EBX,EBX&nbsp;<br>&nbsp;MOV&nbsp;&nbsp;BL, BYTE[ SectorsPerCluster]<br>&nbsp;MUL&nbsp;&nbsp;EBX&nbsp;<br>&nbsp;ADD&nbsp;&nbsp;EAX,DWORD[ BP- DATA_START_SECTOR]<br>&nbsp;MOV&nbsp;&nbsp;DWORD[ BP - DAP_SECTOR_LOW &nbsp;], EAX<br>&nbsp;MOV&nbsp;&nbsp;DL,[SectorsPerCluster]</p><p>&nbsp;; 設置緩沖區<br>&nbsp;MOV&nbsp;&nbsp;WORD [ BP - DAP_BUFFER_SEG &nbsp; ],CX<br>&nbsp;MOV&nbsp;&nbsp;WORD [ BP - DAP_BUFFER_OFF &nbsp; ],00H<br>&nbsp;&nbsp;&nbsp;<br>&nbsp;; 每個簇需要讀取的扇區數<br>&nbsp;MOV&nbsp;&nbsp;BL , BYTE [SectorsPerCluster]</p><p>_NEXT_DATA_SECTOR:<br>&nbsp;; 讀取簇中的每個扇區(內層循環)<br>&nbsp;; 注意 : 通過檢查文件大小，可以避免讀取最后一個不滿簇的所有大小<br>&nbsp;; 讀取數據扇區<br>&nbsp;CALL &nbsp;ReadSector<br>&nbsp;<br>&nbsp;; 更新地址，繼續讀取<br>&nbsp;MOV&nbsp;&nbsp;AX, WORD [BytesPerSector]<br>&nbsp;ADD&nbsp;&nbsp;WORD&nbsp; [BP - DAP_BUFFER_OFF],AX <br>&nbsp;INC&nbsp;&nbsp;DWORD [BP - DAP_SECTOR_LOW]&nbsp;&nbsp;; 遞增扇區號<br>&nbsp;DEC &nbsp;BL&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;; 內層循環計數<br>&nbsp;JNZ&nbsp;&nbsp;_NEXT_DATA_SECTOR<br>&nbsp;&nbsp;<br>&nbsp;<br>&nbsp;; 檢查下一個簇<br>&nbsp;&nbsp;<br>&nbsp;; 更新讀取下一個簇的緩沖區地址<br>&nbsp;MOV&nbsp;&nbsp;CL,BYTE [ SectorsPerCluster ]<br>&nbsp;MOV&nbsp;&nbsp;AX ,WORD [BytesPerSector]<br>&nbsp;SHR&nbsp;&nbsp;AX ,4<br>&nbsp;MUL&nbsp;&nbsp;CL<br>&nbsp;ADD&nbsp;&nbsp;AX ,WORD [ BP - DAP_BUFFER_SEG ] <br>&nbsp;MOV&nbsp;&nbsp;CX,AX ; 保存下一個簇的緩沖區段地址<br>&nbsp;<br>&nbsp;;====================================================================<br>&nbsp;;<br>&nbsp;; 檢查是否還有下一個簇(讀取FAT表的相關信息)<br>&nbsp;;&nbsp;&nbsp;LET&nbsp; &nbsp;N = 數據簇號<br>&nbsp;;&nbsp;&nbsp;THUS&nbsp;FAT_BYTES &nbsp;= N*4&nbsp;&nbsp;(FAT32)<br>&nbsp;;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;FAT_SECTOR&nbsp;= FAT_BYTES / BytesPerSector<br>&nbsp;;&nbsp;&nbsp;&nbsp;&nbsp;FAT_OFFSET&nbsp;= FAT_BYTES % BytesPerSector<br>&nbsp;;<br>&nbsp;;====================================================================<br>&nbsp;<br>&nbsp;; 計算FAT所在的簇號和偏移 <br>&nbsp;MOV&nbsp;&nbsp;EAX,DWORD [BP - CURRENT_CLUSTER]<br>&nbsp;XOR&nbsp;&nbsp;EDX,EDX<br>&nbsp;SHL&nbsp;&nbsp;EAX,2<br>&nbsp;XOR&nbsp;&nbsp;EBX,EBX<br>&nbsp;MOV&nbsp;&nbsp;BX,WORD [ BytesPerSector ]<br>&nbsp;DIV&nbsp;&nbsp;EBX&nbsp;&nbsp;&nbsp;; EAX = Sector&nbsp; EDX = Offset<br>&nbsp;<br>&nbsp;; 設置緩沖區地址<br>&nbsp;ADD&nbsp;&nbsp;EAX,DWORD [BP - FAT_START_SECTOR&nbsp; ]<br>&nbsp;MOV&nbsp;&nbsp;DWORD [ BP - DAP_SECTOR_LOW ], EAX <br>&nbsp;MOV&nbsp; &nbsp;WORD [BP - DAP_BUFFER_SEG&nbsp; ], 00H <br>&nbsp;MOV &nbsp;WORD [BP - DAP_BUFFER_OFF&nbsp; ], DATA_BUF_OFF&nbsp;; 0000:1000H</p><p>&nbsp;; 讀取扇區<br>&nbsp;CALL &nbsp;ReadSector<br>&nbsp;&nbsp;<br>&nbsp;; 檢查下一個簇<br>&nbsp;MOV&nbsp;&nbsp;DI,DX<br>&nbsp;ADD&nbsp;&nbsp;DI,DATA_BUF_OFF<br>&nbsp;MOV&nbsp;&nbsp;EAX,DWORD[DI]&nbsp;&nbsp;; EAX = 下一個要讀的簇號<br>&nbsp;AND&nbsp;&nbsp;EAX,CLUSTER_MASK<br>&nbsp;MOV&nbsp;&nbsp;DWORD[ BP - CURRENT_CLUSTER ],EAX<br>&nbsp;CMP&nbsp;&nbsp;EAX,CLUSTER_LAST&nbsp;&nbsp;; CX &gt;= 0FFFFFF8H，則意味著沒有更多的簇了<br>&nbsp;JB&nbsp;&nbsp;_NEXT_DATA_CLUSTER</p><p>;讀取完畢<br>_RUN_LOADER:&nbsp;</p><p>&nbsp;; 運行FDOSLDR.BIN<br>&nbsp;MOV&nbsp;&nbsp;DL,[DriveNumber]<br>&nbsp;JMP&nbsp;&nbsp;00:OSLOADER_ADDR</p><p>;====================================================================<br>; 調試例程<br>;====================================================================<br>%IFDEF DEBUG<br>;====================================================================</p><p>;====================================================================<br>; <br>; 顯示一個字符<br>;&nbsp;輸入： AL = 待顯示字符<br>;<br>;====================================================================<br>PrintChar:<br>&nbsp;PUSH&nbsp;BX<br>&nbsp;MOV &nbsp;AH,0EH<br>&nbsp;MOV&nbsp;&nbsp;BX,7<br>&nbsp;INT&nbsp;&nbsp;10H<br>&nbsp;POP &nbsp;BX<br>&nbsp;RET<br>&nbsp;<br>;====================================================================<br>%ENDIF ; DEBUG<br>;====================================================================</p><p><br>;====================================================================<br>; 扇區最后的標記字節(NASM不支持重復ORG)<br>;====================================================================<br>SecondPadding&nbsp;&nbsp;TIMES 1022-($-$$)&nbsp;db &nbsp;00H<br>SecondSignature&nbsp;&nbsp;DW&nbsp;0AA55H</p><p>;====================================================================<br>; 代碼結束<br>;====================================================================</p><p>&nbsp;&nbsp; </p></span>
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