DuetPkg/BootSector/bootsect.asm - third_party/edk2 - Git at Google

 ;------------------------------------------------------------------------------
 ;*
 ;*   Copyright 2006 - 2007, Intel Corporation
 ;*   All rights reserved. This program and the accompanying materials
 ;*   are licensed and made available under the terms and conditions of the BSD License
 ;*   which accompanies this distribution.  The full text of the license may be found at
 ;*   http://opensource.org/licenses/bsd-license.php
 ;*
 ;*   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
 ;*   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 ;*
 ;*   bootsect.asm
 ;*
 ;*   bootsect.asm is built as 16-bit binary file in 512 bytes and patched to disk/partition's
 ;*   first section - boot sector.
 ;*
 ;*   The startup sequence for DUET disk boot sector is:
 ;*
 ;*   1, LegacyBios check 0xAA55 signature at boot sectore offset 0x1FE to judget
 ;*      whether disk/partition is bootable.
 ;*   2, LegacyBios will load boot sector to 0x7c00 in real mode, pass BPB data and
 ;*      hand off control to 0x7c00 code.
 ;*   3, boot sector code simply parse FAT format in boot disk and find EfiLdr binary file
 ;*      and EfiVar.bin if exists. For first boot, EfiVar.bin does not exist.
 ;*   4, boot sector load the first sector of EfiLdr binary which is start.com to
 ;*      0x2000:0x0000 address.
 ;*   5, boot sector handoff control to 0x2000:0x0000 for start.com binary.
 ;*
 ;------------------------------------------------------------------------------

         .model  small
         .stack
         .486p
         .code

 FAT_DIRECTORY_ENTRY_SIZE  EQU     020h
 FAT_DIRECTORY_ENTRY_SHIFT EQU     5
 BLOCK_SIZE                EQU     0200h
 BLOCK_MASK                EQU     01ffh
 BLOCK_SHIFT               EQU     9
                                                ; "EFILDR_____"
 LOADER_FILENAME_PART1     EQU     04c494645h   ; "EFIL"
 LOADER_FILENAME_PART2     EQU     020205244h   ; "DR__"
 LOADER_FILENAME_PART3     EQU     020202020h   ; "____"

         org 0h
 Ia32Jump:
   jmp   BootSectorEntryPoint  ; JMP inst                  - 3 bytes
   nop

 OemId             db  "INTEL   "    ; OemId               - 8 bytes
 ; BPB data below will be fixed by tool
 SectorSize        dw  0             ; Sector Size         - 16 bits
 SectorsPerCluster db  0             ; Sector Per Cluster  - 8 bits
 ReservedSectors   dw  0             ; Reserved Sectors    - 16 bits
 NoFats            db  0             ; Number of FATs      - 8 bits
 RootEntries       dw  0             ; Root Entries        - 16 bits
 Sectors           dw  0             ; Number of Sectors   - 16 bits
 Media             db  0             ; Media               - 8 bits  - ignored
 SectorsPerFat     dw  0             ; Sectors Per FAT     - 16 bits
 SectorsPerTrack   dw  0             ; Sectors Per Track   - 16 bits - ignored
 Heads             dw  0             ; Heads               - 16 bits - ignored
 HiddenSectors     dd  0             ; Hidden Sectors      - 32 bits - ignored
 LargeSectors      dd  0             ; Large Sectors       - 32 bits
 PhysicalDrive     db  0             ; PhysicalDriveNumber - 8 bits  - ignored
 CurrentHead       db  0             ; Current Head        - 8 bits
 Signature         db  0             ; Signature           - 8 bits  - ignored
 Id                db  "    "        ; Id                  - 4 bytes
 FatLabel          db  "           " ; Label               - 11 bytes
 SystemId          db  "FAT12   "    ; SystemId            - 8 bytes

 BootSectorEntryPoint:
         ASSUME  ds:@code
         ASSUME  ss:@code

 ; ****************************************************************************
 ; Start Print
 ; ****************************************************************************
   lea  si, cs:[StartString]
   call PrintString

 ; ****************************************************************************
 ; Print over
 ; ****************************************************************************

   mov   ax,cs         ; ax = 0
   mov   ss,ax         ; ss = 0
   add   ax,1000h
   mov   ds,ax

   mov   sp,07c00h     ; sp = 0x7c00
   mov   bp,sp         ; bp = 0x7c00

   mov   ah,8                                ; ah = 8 - Get Drive Parameters Function
   mov   byte ptr [bp+PhysicalDrive],dl      ; BBS defines that BIOS would pass the booting driver number to the loader through DL
   int   13h                                 ; Get Drive Parameters
   xor   ax,ax                               ; ax = 0
   mov   al,dh                               ; al = dh (number of sides (0 based))
   inc   al                                  ; MaxHead = al + 1
   push  ax                                  ; 0000:7bfe = MaxHead
   mov   al,cl                               ; al = cl (CL = sectors per track)
   and   al,03fh                             ; MaxSector = al & 0x3f
   push  ax                                  ; 0000:7bfc = MaxSector

   cmp   word ptr [bp+SectorSignature],0aa55h  ; Verify Boot Sector Signature
   jne   BadBootSector
   mov   cx,word ptr [bp+RootEntries]      ; cx = RootEntries
   shl   cx,FAT_DIRECTORY_ENTRY_SHIFT      ; cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes
   mov   bx,cx                             ; bx = size of the Root Directory in bytes
   and   bx,BLOCK_MASK                     ; See if it is an even number of sectors long
   jne   BadBootSector                     ; If is isn't, then the boot sector is bad.
   mov   bx,cx                             ; bx = size of the Root Directory in bytes
   shr   bx,BLOCK_SHIFT                    ; bx = size of Root Directory in sectors
   mov   al,byte ptr [bp+NoFats]           ; al = NoFats
   xor   ah,ah                             ; ah = 0  ==> ax = NoFats
   mul   word ptr [bp+SectorsPerFat]       ; ax = NoFats * SectorsPerFat
   add   ax,word ptr [bp+ReservedSectors]  ; ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA
   push  ds
   pop   es
   xor   di,di                             ; Store directory in es:di = 1000:0000
   call  ReadBlocks                        ; Read entire Root Directory
   add   ax,bx                             ; ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector)
   mov   word ptr [bp],ax                  ; Save FirstClusterLBA (FirstDataSector) for later use

   ; dx - variable storage (initial value is 0)
   ; bx - loader (initial value is 0)
   xor   dx, dx
   xor   bx, bx

 FindEFILDR:
   cmp   dword ptr [di],LOADER_FILENAME_PART1         ; Compare to "EFIL"
   jne   FindVARSTORE
   cmp   dword ptr [di+4],LOADER_FILENAME_PART2
   jne   FindVARSTORE
   cmp   dword ptr [di+7],LOADER_FILENAME_PART3
   jne   FindVARSTORE
   mov   bx, word ptr [di+26]              ; bx = Start Cluster for EFILDR  <----------------------------------
   test  dx, dx
   je    FindNext                          ; Efivar.bin is not loaded
   jmp   FoundAll

 FindVARSTORE:
   ; if the file is not loader file, see if it's "EFIVAR  BIN"
   cmp   dword ptr [di], 056494645h        ; Compare to "EFIV"
   jne   FindNext
   cmp   dword ptr [di+4], 020205241h      ; Compare to "AR  "
   jne   FindNext
   cmp   dword ptr [di+7], 04e494220h      ; Compare to " BIN"
   jne   FindNext
   mov   dx, di                            ; dx = Offset of Start Cluster for Efivar.bin <---------------------
   add   dx, 26
   test  bx, bx
   je    FindNext                          ; Efildr is not loaded
   jmp   FoundAll

 FindNext:
   ; go to next find
   add   di,FAT_DIRECTORY_ENTRY_SIZE       ; Increment di
   sub   cx,FAT_DIRECTORY_ENTRY_SIZE       ; Decrement cx
   ; TODO: jump to FindVarStore if ...
   jne   FindEFILDR
   jmp   NotFoundAll

 FoundAll:
 FoundEFILDR:                                  ; 0x7cfe
   mov     cx,bx                               ; cx = Start Cluster for EFILDR  <----------------------------------
   mov     ax,cs                               ; Destination = 2000:0000
   add     ax,2000h
   mov     es,ax
   xor     di,di
 ReadFirstClusterOfEFILDR:
   mov     ax,cx                               ; ax = StartCluster
   sub     ax,2                                ; ax = StartCluster - 2
   xor     bh,bh
   mov     bl,byte ptr [bp+SectorsPerCluster]  ; bx = SectorsPerCluster
   push    dx
   mul     bx
   pop     dx                                  ; ax = (StartCluster - 2) * SectorsPerCluster
   add     ax, word ptr [bp]                   ; ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster
   xor     bh,bh
   mov     bl,byte ptr [bp+SectorsPerCluster]  ; bx = Number of Sectors in a cluster
   push    es
   call    ReadBlocks
   pop     ax
 JumpIntoFirstSectorOfEFILDR:
   mov     word ptr [bp+JumpSegment],ax        ; 0x7d26
 JumpFarInstruction:                           ; 0x7d2a
   db      0eah
 JumpOffset:
   dw      0000h
 JumpSegment:
   dw      2000h


 PrintString:
   mov  ax,0b800h
   mov  es,ax
   mov  ax, 07c0h
   mov  ds, ax
   mov  cx, 7
   mov  di, 160
   rep  movsw
   ret
 ; ****************************************************************************
 ; ReadBlocks - Reads a set of blocks from a block device
 ;
 ; AX    = Start LBA
 ; BX    = Number of Blocks to Read
 ; ES:DI = Buffer to store sectors read from disk
 ; ****************************************************************************

 ; cx = Blocks
 ; bx = NumberOfBlocks
 ; si = StartLBA

 ReadBlocks:
   pusha
   add     eax,dword ptr [bp+LBAOffsetForBootSector]    ; Add LBAOffsetForBootSector to Start LBA
   add     eax,dword ptr [bp+HiddenSectors]    ; Add HiddenSectors to Start LBA
   mov     esi,eax                             ; esi = Start LBA
   mov     cx,bx                               ; cx = Number of blocks to read
 ReadCylinderLoop:
   mov     bp,07bfch                           ; bp = 0x7bfc
   mov     eax,esi                             ; eax = Start LBA
   xor     edx,edx                             ; edx = 0
   movzx   ebx,word ptr [bp]                   ; bx = MaxSector
   div     ebx                                 ; ax = StartLBA / MaxSector
   inc     dx                                  ; dx = (StartLBA % MaxSector) + 1
   sub     bx,dx                               ; bx = MaxSector - Sector
   inc     bx                                  ; bx = MaxSector - Sector + 1
   cmp     cx,bx                               ; Compare (Blocks) to (MaxSector - Sector + 1)
   jg      LimitTransfer
   mov     bx,cx                               ; bx = Blocks
 LimitTransfer:
   push    cx
   mov     cl,dl                               ; cl = (StartLBA % MaxSector) + 1 = Sector
   xor     dx,dx                               ; dx = 0
   div     word ptr [bp+2]                     ; ax = ax / (MaxHead + 1) = Cylinder
                                               ; dx = ax % (MaxHead + 1) = Head

   push    bx                                  ; Save number of blocks to transfer
   mov     dh,dl                               ; dh = Head
   mov     bp,07c00h                           ; bp = 0x7c00
   mov     dl,byte ptr [bp+PhysicalDrive]      ; dl = Drive Number
   mov     ch,al                               ; ch = Cylinder
   mov     al,bl                               ; al = Blocks
   mov     ah,2                                ; ah = Function 2
   mov     bx,di                               ; es:bx = Buffer address
   int     013h
   jc      DiskError
   pop     bx
   pop     cx
   movzx   ebx,bx
   add     esi,ebx                             ; StartLBA = StartLBA + NumberOfBlocks
   sub     cx,bx                               ; Blocks = Blocks - NumberOfBlocks
   mov     ax,es
   shl     bx,(BLOCK_SHIFT-4)
   add     ax,bx
   mov     es,ax                               ; es:di = es:di + NumberOfBlocks*BLOCK_SIZE
   cmp     cx,0
   jne     ReadCylinderLoop
   popa
   ret

 ; ****************************************************************************
 ; ERROR Condition:
 ; ****************************************************************************
 NotFoundAll:                            ; 0x7da6
   ; if we found EFILDR, continue
   test bx,bx
   jne  FoundEFILDR
 BadBootSector:
 DiskError:
   lea  si, cs:[ErrorString]
   call PrintString
 Halt:
   jmp   Halt

 StartString:
   db 'B', 0ch, 'S', 0ch, 't', 0ch, 'a', 0ch, 'r', 0ch, 't', 0ch, '!', 0ch
 ErrorString:
   db 'B', 0ch, 'E', 0ch, 'r', 0ch, 'r', 0ch, 'o', 0ch, 'r', 0ch, '!', 0ch

 ; ****************************************************************************
 ; LBA Offset for BootSector, need patched by tool for HD boot.
 ; ****************************************************************************

   org 01fah
 LBAOffsetForBootSector:
   dd        0h

 ; ****************************************************************************
 ; Sector Signature
 ; ****************************************************************************

   org 01feh
 SectorSignature:
   dw        0aa55h      ; Boot Sector Signature

   end
	;------------------------------------------------------------------------------
	;*
	;* Copyright 2006 - 2007, Intel Corporation
	;* All rights reserved. This program and the accompanying materials
	;* are licensed and made available under the terms and conditions of the BSD License
	;* which accompanies this distribution. The full text of the license may be found at
	;* http://opensource.org/licenses/bsd-license.php
	;*
	;* THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
	;* WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
	;*
	;* bootsect.asm
	;*
	;* bootsect.asm is built as 16-bit binary file in 512 bytes and patched to disk/partition's
	;* first section - boot sector.
	;*
	;* The startup sequence for DUET disk boot sector is:
	;*
	;* 1, LegacyBios check 0xAA55 signature at boot sectore offset 0x1FE to judget
	;* whether disk/partition is bootable.
	;* 2, LegacyBios will load boot sector to 0x7c00 in real mode, pass BPB data and
	;* hand off control to 0x7c00 code.
	;* 3, boot sector code simply parse FAT format in boot disk and find EfiLdr binary file
	;* and EfiVar.bin if exists. For first boot, EfiVar.bin does not exist.
	;* 4, boot sector load the first sector of EfiLdr binary which is start.com to
	;* 0x2000:0x0000 address.
	;* 5, boot sector handoff control to 0x2000:0x0000 for start.com binary.
	;*
	;------------------------------------------------------------------------------

	.model small
	.stack
	.486p
	.code

	FAT_DIRECTORY_ENTRY_SIZE EQU 020h
	FAT_DIRECTORY_ENTRY_SHIFT EQU 5
	BLOCK_SIZE EQU 0200h
	BLOCK_MASK EQU 01ffh
	BLOCK_SHIFT EQU 9
	; "EFILDR_____"
	LOADER_FILENAME_PART1 EQU 04c494645h ; "EFIL"
	LOADER_FILENAME_PART2 EQU 020205244h ; "DR__"
	LOADER_FILENAME_PART3 EQU 020202020h ; "____"

	org 0h
	Ia32Jump:
	jmp BootSectorEntryPoint ; JMP inst - 3 bytes
	nop

	OemId db "INTEL " ; OemId - 8 bytes
	; BPB data below will be fixed by tool
	SectorSize dw 0 ; Sector Size - 16 bits
	SectorsPerCluster db 0 ; Sector Per Cluster - 8 bits
	ReservedSectors dw 0 ; Reserved Sectors - 16 bits
	NoFats db 0 ; Number of FATs - 8 bits
	RootEntries dw 0 ; Root Entries - 16 bits
	Sectors dw 0 ; Number of Sectors - 16 bits
	Media db 0 ; Media - 8 bits - ignored
	SectorsPerFat dw 0 ; Sectors Per FAT - 16 bits
	SectorsPerTrack dw 0 ; Sectors Per Track - 16 bits - ignored
	Heads dw 0 ; Heads - 16 bits - ignored
	HiddenSectors dd 0 ; Hidden Sectors - 32 bits - ignored
	LargeSectors dd 0 ; Large Sectors - 32 bits
	PhysicalDrive db 0 ; PhysicalDriveNumber - 8 bits - ignored
	CurrentHead db 0 ; Current Head - 8 bits
	Signature db 0 ; Signature - 8 bits - ignored
	Id db " " ; Id - 4 bytes
	FatLabel db " " ; Label - 11 bytes
	SystemId db "FAT12 " ; SystemId - 8 bytes

	BootSectorEntryPoint:
	ASSUME ds:@code
	ASSUME ss:@code

	; ****************************************************************************
	; Start Print
	; ****************************************************************************
	lea si, cs:[StartString]
	call PrintString

	; ****************************************************************************
	; Print over
	; ****************************************************************************

	mov ax,cs ; ax = 0
	mov ss,ax ; ss = 0
	add ax,1000h
	mov ds,ax

	mov sp,07c00h ; sp = 0x7c00
	mov bp,sp ; bp = 0x7c00

	mov ah,8 ; ah = 8 - Get Drive Parameters Function
	mov byte ptr [bp+PhysicalDrive],dl ; BBS defines that BIOS would pass the booting driver number to the loader through DL
	int 13h ; Get Drive Parameters
	xor ax,ax ; ax = 0
	mov al,dh ; al = dh (number of sides (0 based))
	inc al ; MaxHead = al + 1
	push ax ; 0000:7bfe = MaxHead
	mov al,cl ; al = cl (CL = sectors per track)
	and al,03fh ; MaxSector = al & 0x3f
	push ax ; 0000:7bfc = MaxSector

	cmp word ptr [bp+SectorSignature],0aa55h ; Verify Boot Sector Signature
	jne BadBootSector
	mov cx,word ptr [bp+RootEntries] ; cx = RootEntries
	shl cx,FAT_DIRECTORY_ENTRY_SHIFT ; cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes
	mov bx,cx ; bx = size of the Root Directory in bytes
	and bx,BLOCK_MASK ; See if it is an even number of sectors long
	jne BadBootSector ; If is isn't, then the boot sector is bad.
	mov bx,cx ; bx = size of the Root Directory in bytes
	shr bx,BLOCK_SHIFT ; bx = size of Root Directory in sectors
	mov al,byte ptr [bp+NoFats] ; al = NoFats
	xor ah,ah ; ah = 0 ==> ax = NoFats
	mul word ptr [bp+SectorsPerFat] ; ax = NoFats * SectorsPerFat
	add ax,word ptr [bp+ReservedSectors] ; ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA
	push ds
	pop es
	xor di,di ; Store directory in es:di = 1000:0000
	call ReadBlocks ; Read entire Root Directory
	add ax,bx ; ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector)
	mov word ptr [bp],ax ; Save FirstClusterLBA (FirstDataSector) for later use

	; dx - variable storage (initial value is 0)
	; bx - loader (initial value is 0)
	xor dx, dx
	xor bx, bx

	FindEFILDR:
	cmp dword ptr [di],LOADER_FILENAME_PART1 ; Compare to "EFIL"
	jne FindVARSTORE
	cmp dword ptr [di+4],LOADER_FILENAME_PART2
	jne FindVARSTORE
	cmp dword ptr [di+7],LOADER_FILENAME_PART3
	jne FindVARSTORE
	mov bx, word ptr [di+26] ; bx = Start Cluster for EFILDR <----------------------------------
	test dx, dx
	je FindNext ; Efivar.bin is not loaded
	jmp FoundAll

	FindVARSTORE:
	; if the file is not loader file, see if it's "EFIVAR BIN"
	cmp dword ptr [di], 056494645h ; Compare to "EFIV"
	jne FindNext
	cmp dword ptr [di+4], 020205241h ; Compare to "AR "
	jne FindNext
	cmp dword ptr [di+7], 04e494220h ; Compare to " BIN"
	jne FindNext
	mov dx, di ; dx = Offset of Start Cluster for Efivar.bin <---------------------
	add dx, 26
	test bx, bx
	je FindNext ; Efildr is not loaded
	jmp FoundAll

	FindNext:
	; go to next find
	add di,FAT_DIRECTORY_ENTRY_SIZE ; Increment di
	sub cx,FAT_DIRECTORY_ENTRY_SIZE ; Decrement cx
	; TODO: jump to FindVarStore if ...
	jne FindEFILDR
	jmp NotFoundAll

	FoundAll:
	FoundEFILDR: ; 0x7cfe
	mov cx,bx ; cx = Start Cluster for EFILDR <----------------------------------
	mov ax,cs ; Destination = 2000:0000
	add ax,2000h
	mov es,ax
	xor di,di
	ReadFirstClusterOfEFILDR:
	mov ax,cx ; ax = StartCluster
	sub ax,2 ; ax = StartCluster - 2
	xor bh,bh
	mov bl,byte ptr [bp+SectorsPerCluster] ; bx = SectorsPerCluster
	push dx
	mul bx
	pop dx ; ax = (StartCluster - 2) * SectorsPerCluster
	add ax, word ptr [bp] ; ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster
	xor bh,bh
	mov bl,byte ptr [bp+SectorsPerCluster] ; bx = Number of Sectors in a cluster
	push es
	call ReadBlocks
	pop ax
	JumpIntoFirstSectorOfEFILDR:
	mov word ptr [bp+JumpSegment],ax ; 0x7d26
	JumpFarInstruction: ; 0x7d2a
	db 0eah
	JumpOffset:
	dw 0000h
	JumpSegment:
	dw 2000h


	PrintString:
	mov ax,0b800h
	mov es,ax
	mov ax, 07c0h
	mov ds, ax
	mov cx, 7
	mov di, 160
	rep movsw
	ret
	; ****************************************************************************
	; ReadBlocks - Reads a set of blocks from a block device
	;
	; AX = Start LBA
	; BX = Number of Blocks to Read
	; ES:DI = Buffer to store sectors read from disk
	; ****************************************************************************

	; cx = Blocks
	; bx = NumberOfBlocks
	; si = StartLBA

	ReadBlocks:
	pusha
	add eax,dword ptr [bp+LBAOffsetForBootSector] ; Add LBAOffsetForBootSector to Start LBA
	add eax,dword ptr [bp+HiddenSectors] ; Add HiddenSectors to Start LBA
	mov esi,eax ; esi = Start LBA
	mov cx,bx ; cx = Number of blocks to read
	ReadCylinderLoop:
	mov bp,07bfch ; bp = 0x7bfc
	mov eax,esi ; eax = Start LBA
	xor edx,edx ; edx = 0
	movzx ebx,word ptr [bp] ; bx = MaxSector
	div ebx ; ax = StartLBA / MaxSector
	inc dx ; dx = (StartLBA % MaxSector) + 1
	sub bx,dx ; bx = MaxSector - Sector
	inc bx ; bx = MaxSector - Sector + 1
	cmp cx,bx ; Compare (Blocks) to (MaxSector - Sector + 1)
	jg LimitTransfer
	mov bx,cx ; bx = Blocks
	LimitTransfer:
	push cx
	mov cl,dl ; cl = (StartLBA % MaxSector) + 1 = Sector
	xor dx,dx ; dx = 0
	div word ptr [bp+2] ; ax = ax / (MaxHead + 1) = Cylinder
	; dx = ax % (MaxHead + 1) = Head

	push bx ; Save number of blocks to transfer
	mov dh,dl ; dh = Head
	mov bp,07c00h ; bp = 0x7c00
	mov dl,byte ptr [bp+PhysicalDrive] ; dl = Drive Number
	mov ch,al ; ch = Cylinder
	mov al,bl ; al = Blocks
	mov ah,2 ; ah = Function 2
	mov bx,di ; es:bx = Buffer address
	int 013h
	jc DiskError
	pop bx
	pop cx
	movzx ebx,bx
	add esi,ebx ; StartLBA = StartLBA + NumberOfBlocks
	sub cx,bx ; Blocks = Blocks - NumberOfBlocks
	mov ax,es
	shl bx,(BLOCK_SHIFT-4)
	add ax,bx
	mov es,ax ; es:di = es:di + NumberOfBlocks*BLOCK_SIZE
	cmp cx,0
	jne ReadCylinderLoop
	popa
	ret

	; ****************************************************************************
	; ERROR Condition:
	; ****************************************************************************
	NotFoundAll: ; 0x7da6
	; if we found EFILDR, continue
	test bx,bx
	jne FoundEFILDR
	BadBootSector:
	DiskError:
	lea si, cs:[ErrorString]
	call PrintString
	Halt:
	jmp Halt

	StartString:
	db 'B', 0ch, 'S', 0ch, 't', 0ch, 'a', 0ch, 'r', 0ch, 't', 0ch, '!', 0ch
	ErrorString:
	db 'B', 0ch, 'E', 0ch, 'r', 0ch, 'r', 0ch, 'o', 0ch, 'r', 0ch, '!', 0ch

	; ****************************************************************************
	; LBA Offset for BootSector, need patched by tool for HD boot.
	; ****************************************************************************

	org 01fah
	LBAOffsetForBootSector:
	dd 0h

	; ****************************************************************************
	; Sector Signature
	; ****************************************************************************

	org 01feh
	SectorSignature:
	dw 0aa55h ; Boot Sector Signature

	end