[mirror_edk2.git] / DuetPkg / BootSector / bootsect.S

#------------------------------------------------------------------------------\r
#*\r
#*   Copyright 2006 - 2007, Intel Corporation                                                         \r
#*   All rights reserved. This program and the accompanying materials                          \r
#*   are licensed and made available under the terms and conditions of the BSD License         \r
#*   which accompanies this distribution.  The full text of the license may be found at        \r
#*   http://opensource.org/licenses/bsd-license.php                                            \r
#*                                                                                             \r
#*   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     \r
#*   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             \r
#*   \r
#*    bootsect.asm\r
#*  \r
#*   Abstract:\r
#*\r
#------------------------------------------------------------------------------\r
\r
        #.MODEL small\r
        .stack: \r
        .486p: \r
        .code: \r
\r
.equ                      FAT_DIRECTORY_ENTRY_SIZE, 0x020\r
.equ                      FAT_DIRECTORY_ENTRY_SHIFT, 5\r
.equ                      BLOCK_SIZE, 0x0200\r
.equ                      BLOCK_MASK, 0x01ff\r
.equ                      BLOCK_SHIFT, 9\r
                                               # "EFILDR_____"\r
.equ                      LOADER_FILENAME_PART1, 0x04c494645    # "EFIL"\r
.equ                      LOADER_FILENAME_PART2, 0x020205244    # "DR__"\r
.equ                      LOADER_FILENAME_PART3, 0x020202020    # "____"\r
\r
        .org 0x0\r
Ia32Jump: \r
  jmp   BootSectorEntryPoint  # JMP inst                  - 3 bytes\r
  nop\r
\r
OemId:              .ascii   "INTEL   "       # OemId               - 8 bytes\r
# BPB data below will be fixed by tool\r
SectorSize:         .word  0                  # Sector Size         - 16 bits\r
SectorsPerCluster:  .byte  0                  # Sector Per Cluster  - 8 bits\r
ReservedSectors:    .word  0                  # Reserved Sectors    - 16 bits\r
NoFats:             .byte  0                  # Number of FATs      - 8 bits\r
RootEntries:        .word  0                  # Root Entries        - 16 bits\r
Sectors:            .word  0                  # Number of Sectors   - 16 bits\r
Media:              .byte  0                  # Media               - 8 bits  - ignored\r
SectorsPerFat:      .word  0                  # Sectors Per FAT     - 16 bits\r
SectorsPerTrack:    .word  0                  # Sectors Per Track   - 16 bits - ignored\r
Heads:              .word  0                  # Heads               - 16 bits - ignored\r
HiddenSectors:      .long  0                  # Hidden Sectors      - 32 bits - ignored\r
LargeSectors:       .long  0                  # Large Sectors       - 32 bits \r
PhysicalDrive:      .byte  0                  # PhysicalDriveNumber - 8 bits  - ignored\r
CurrentHead:        .byte  0                  # Current Head        - 8 bits\r
Signature:          .byte  0                  # Signature           - 8 bits  - ignored\r
VolId:              .ascii "    "             # Volume Serial Number- 4 bytes\r
FatLabel:           .ascii "           "      # Label               - 11 bytes\r
SystemId:           .ascii "FAT12   "         # SystemId            - 8 bytes\r
\r
BootSectorEntryPoint: \r
        #ASSUME ds:@code\r
        #ASSUME ss:@code\r
\r
# ****************************************************************************\r
# Start Print\r
# ****************************************************************************\r
  leaw %cs:StartString, %si\r
  call PrintString\r
\r
# ****************************************************************************\r
# Print over\r
# ****************************************************************************\r
\r
  movw  %cs, %ax      # ax = 0\r
  movw  %ax, %ss      # ss = 0\r
  addw  $0x1000, %ax\r
  movw  %ax, %ds\r
\r
  movw  $0x7c00, %sp  # sp = 0x7c00\r
  movw  %sp, %bp      # bp = 0x7c00\r
\r
  movb  $8, %ah                             # ah = 8 - Get Drive Parameters Function\r
  movb  %dl, PhysicalDrive(%bp)             # BBS defines that BIOS would pass the booting driver number to the loader through DL\r
  int   $0x13                               # Get Drive Parameters\r
  xorw  %ax, %ax                # ax = 0\r
  movb  %dh, %al                # al = dh\r
  incb  %al                     # MaxHead = al + 1\r
  pushw %ax                     # 0000:7bfe = MaxHead\r
  movb  %cl, %al                # al = cl\r
  andb  $0x3f, %al              # MaxSector = al & 0x3f\r
  pushw %ax                     # 0000:7bfc = MaxSector\r
\r
  cmpw  $0xaa55, SectorSignature(%bp)         # Verify Boot Sector Signature\r
  jne   BadBootSector\r
  movw  RootEntries(%bp), %cx             # cx = RootEntries\r
  shlw  $FAT_DIRECTORY_ENTRY_SHIFT, %cx   # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes\r
  movw  %cx, %bx                          # bx = size of the Root Directory in bytes\r
  andw  $BLOCK_MASK, %bx                  # See if it is an even number of sectors long\r
  jne   BadBootSector                     # If is isn't, then the boot sector is bad.\r
  movw  %cx, %bx                          # bx = size of the Root Directory in bytes\r
  shrw  $BLOCK_SHIFT, %bx                 # bx = size of Root Directory in sectors\r
  movb  NoFats(%bp), %al                  # al = NoFats\r
  xorb  %ah, %ah                          # ah = 0  ==> ax = NoFats\r
  mulw  SectorsPerFat(%bp)                # ax = NoFats * SectorsPerFat\r
  addw  ReservedSectors(%bp), %ax         # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA\r
  pushw %ds\r
  popw  %es\r
  xorw  %di, %di                          # Store directory in es:di = 1000:0000\r
  call  ReadBlocks                        # Read entire Root Directory\r
  addw  %bx, %ax                          # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector)\r
  movw  %ax, (%bp)                        # Save FirstClusterLBA (FirstDataSector) for later use\r
\r
  # dx - variable storage (initial value is 0)\r
  # bx - loader (initial value is 0)\r
  xorw  %dx, %dx\r
  xorw  %bx, %bx\r
\r
FindEFILDR: \r
	cmpl   $LOADER_FILENAME_PART1, (%di)        # Compare to "EFIL"\r
  jne   FindVARSTORE\r
  cmpl   $LOADER_FILENAME_PART2, 4(%di) \r
  jne   FindVARSTORE\r
  cmpl   $LOADER_FILENAME_PART3, 7(%di) \r
  jne   FindVARSTORE\r
  movw  26(%di), %bx                      # bx = Start Cluster for EFILDR  <----------------------------------\r
  testw %dx, %dx\r
  je    FindNext                          # Efivar.bin is not loaded\r
  jmp   FoundAll\r
\r
FindVARSTORE: \r
  ## if the file is not loader file, see if it's "EFIVAR  BIN"\r
  cmpl  $0x56494645, (%di)                # Compare to "EFIV"\r
  jne   FindNext\r
  cmpl  $0x20205241, 4(%di)               # Compare to "AR  "\r
  jne   FindNext\r
  cmpl  $0x4e494220, 7(%di)               # Compare to " BIN"\r
  jne   FindNext\r
  movw  %di, %dx                          # dx = Offset of Start Cluster for Efivar.bin <---------------------\r
  addw  $26, %dx\r
  testw %bx, %bx\r
  je    FindNext                          # Efildr is not loaded\r
  jmp   FoundAll\r
\r
FindNext: \r
  # go to next find\r
  addw  $FAT_DIRECTORY_ENTRY_SIZE, %di    # Increment di\r
  subw  $FAT_DIRECTORY_ENTRY_SIZE, %cx    # Decrement cx\r
  # TODO: jump to FindVarStore if ...\r
  jne   FindEFILDR\r
  jmp   NotFoundAll\r
\r
FoundAll: \r
FoundEFILDR: \r
  movw    %bx, %cx                            # cx = Start Cluster for EFILDR  <----------------------------------\r
  movw    %cs, %ax                            # Destination = 2000:0000\r
  addw    $0x2000, %ax\r
  movw    %ax, %es\r
  xorw    %di, %di\r
ReadFirstClusterOfEFILDR: \r
  movw    %cx, %ax                            # ax = StartCluster\r
  subw    $2, %ax                             # ax = StartCluster - 2\r
  xorb    %bh, %bh\r
  movb    SectorsPerCluster(%bp), %bl         # bx = SectorsPerCluster\r
  pushw   %dx\r
  mulw    %bx\r
  popw    %dx                                 # ax = (StartCluster - 2) * SectorsPerCluster\r
  addw    (%bp), %ax                          # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster\r
  xorb    %bh, %bh\r
  movb    SectorsPerCluster(%bp), %bl         # bx = Number of Sectors in a cluster\r
  pushw   %es\r
  call    ReadBlocks\r
  popw    %ax\r
JumpIntoFirstSectorOfEFILDR: \r
  movw    %ax, JumpSegment(%bp)\r
JumpFarInstruction: \r
  .byte   0xea\r
JumpOffset: \r
  .word   0x000\r
JumpSegment: \r
  .word   0x2000\r
\r
\r
PrintString: \r
  movw $0xb800, %ax\r
  movw %ax, %es\r
  movw $0x7c0, %ax\r
  movw %ax, %ds\r
  movw $7, %cx\r
  movw $160, %di\r
  rep\r
  movsw\r
  ret\r
# ****************************************************************************\r
# ReadBlocks - Reads a set of blocks from a block device\r
#\r
# AX    = Start LBA\r
# BX    = Number of Blocks to Read\r
# ES:DI = Buffer to store sectors read from disk\r
# ****************************************************************************\r
\r
# cx = Blocks\r
# bx = NumberOfBlocks\r
# si = StartLBA\r
\r
ReadBlocks: \r
  pusha\r
  addl    LBAOffsetForBootSector(%bp), %eax            # Add LBAOffsetForBootSector to Start LBA\r
  addl    HiddenSectors(%bp), %eax            # Add HiddenSectors to Start LBA\r
  movl    %eax, %esi                          # esi = Start LBA\r
  movw    %bx, %cx                            # cx = Number of blocks to read\r
ReadCylinderLoop: \r
  movw    $0x7bfc, %bp                        # bp = 0x7bfc\r
  movl    %esi, %eax                          # eax = Start LBA\r
  xorl    %edx, %edx                          # edx = 0\r
  movzwl  (%bp), %ebx                         # bx = MaxSector\r
  divl    %ebx                                # ax = StartLBA / MaxSector\r
  incw    %dx                                 # dx = (StartLBA % MaxSector) + 1\r
  subw    %dx, %bx                            # bx = MaxSector - Sector\r
  incw    %bx                                 # bx = MaxSector - Sector + 1\r
  cmpw    %bx, %cx                            # Compare (Blocks) to (MaxSector - Sector + 1)\r
  jg      LimitTransfer\r
  movw    %cx, %bx                            # bx = Blocks\r
LimitTransfer: \r
  pushw   %cx\r
  movb    %dl, %cl                            # cl = (StartLBA % MaxSector) + 1 = Sector\r
  xorw    %dx, %dx                            # dx = 0\r
  divw    2(%bp)                              # ax = ax / (MaxHead + 1) = Cylinder  \r
                                              # dx = ax % (MaxHead + 1) = Head\r
\r
  pushw   %bx                                 # Save number of blocks to transfer\r
  movb    %dl, %dh                            # dh = Head\r
  movw    $0x7c00, %bp                        # bp = 0x7c00\r
  movb    PhysicalDrive(%bp), %dl             # dl = Drive Number\r
  movb    %al, %ch                            # ch = Cylinder\r
  movb    %bl, %al                            # al = Blocks\r
  movb    $2, %ah                             # ah = Function 2\r
  movw    %di, %bx                            # es:bx = Buffer address\r
  int     $0x13\r
  jc      DiskError\r
  popw    %bx\r
  popw    %cx\r
  movzwl  %bx, %ebx\r
  addl    %ebx, %esi                          # StartLBA = StartLBA + NumberOfBlocks\r
  subw    %bx, %cx                            # Blocks = Blocks - NumberOfBlocks\r
  movw    %es, %ax\r
  shlw    $(BLOCK_SHIFT-4), %bx\r
  addw    %bx, %ax\r
  movw    %ax, %es                            # es:di = es:di + NumberOfBlocks*BLOCK_SIZE\r
  cmpw    $0, %cx\r
  jne     ReadCylinderLoop\r
  popa\r
  ret\r
\r
# ****************************************************************************\r
# ERROR Condition:\r
# ****************************************************************************\r
NotFoundAll: \r
  ## if we found EFILDR, continue\r
  testw %bx, %bx\r
  jne  FoundEFILDR\r
BadBootSector: \r
DiskError: \r
  leaw %cs:ErrorString, %si\r
  call PrintString\r
Halt: \r
  jmp   Halt\r
\r
StartString: \r
  .byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c\r
ErrorString: \r
  .byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c\r
\r
# ****************************************************************************\r
# LBA Offset for BootSector, need patched by tool for HD boot.\r
# ****************************************************************************\r
\r
  # .org 0x01fa   # Comment it for pass build. Should optimise code size. \r
LBAOffsetForBootSector: \r
  .long     0x0\r
\r
# ****************************************************************************\r
# Sector Signature\r
# ****************************************************************************\r
\r
  # .org 0x01fe    # Comment it for pass build.\r
SectorSignature: \r
  .word     0xaa55      # Boot Sector Signature\r
\r
\r
\r
Commit	Line	Data
819958c6	1	#------------------------------------------------------------------------------\r
	2	#*\r
	3	#* Copyright 2006 - 2007, Intel Corporation \r
	4	#* All rights reserved. This program and the accompanying materials \r
	5	#* are licensed and made available under the terms and conditions of the BSD License \r
	6	#* which accompanies this distribution. The full text of the license may be found at \r
	7	#* http://opensource.org/licenses/bsd-license.php \r
	8	#* \r
	9	#* THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, \r
	10	#* WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. \r
	11	#* \r
	12	#* bootsect.asm\r
	13	#* \r
	14	#* Abstract:\r
	15	#*\r
	16	#------------------------------------------------------------------------------\r
	17	\r
	18	#.MODEL small\r
	19	.stack: \r
	20	.486p: \r
	21	.code: \r
	22	\r
	23	.equ FAT_DIRECTORY_ENTRY_SIZE, 0x020\r
	24	.equ FAT_DIRECTORY_ENTRY_SHIFT, 5\r
	25	.equ BLOCK_SIZE, 0x0200\r
	26	.equ BLOCK_MASK, 0x01ff\r
	27	.equ BLOCK_SHIFT, 9\r
	28	# "EFILDR_____"\r
	29	.equ LOADER_FILENAME_PART1, 0x04c494645 # "EFIL"\r
	30	.equ LOADER_FILENAME_PART2, 0x020205244 # "DR__"\r
	31	.equ LOADER_FILENAME_PART3, 0x020202020 # "____"\r
	32	\r
	33	.org 0x0\r
	34	Ia32Jump: \r
	35	jmp BootSectorEntryPoint # JMP inst - 3 bytes\r
	36	nop\r
	37	\r
	38	OemId: .ascii "INTEL " # OemId - 8 bytes\r
	39	# BPB data below will be fixed by tool\r
	40	SectorSize: .word 0 # Sector Size - 16 bits\r
	41	SectorsPerCluster: .byte 0 # Sector Per Cluster - 8 bits\r
	42	ReservedSectors: .word 0 # Reserved Sectors - 16 bits\r
	43	NoFats: .byte 0 # Number of FATs - 8 bits\r
	44	RootEntries: .word 0 # Root Entries - 16 bits\r
	45	Sectors: .word 0 # Number of Sectors - 16 bits\r
	46	Media: .byte 0 # Media - 8 bits - ignored\r
	47	SectorsPerFat: .word 0 # Sectors Per FAT - 16 bits\r
	48	SectorsPerTrack: .word 0 # Sectors Per Track - 16 bits - ignored\r
	49	Heads: .word 0 # Heads - 16 bits - ignored\r
	50	HiddenSectors: .long 0 # Hidden Sectors - 32 bits - ignored\r
	51	LargeSectors: .long 0 # Large Sectors - 32 bits \r
	52	PhysicalDrive: .byte 0 # PhysicalDriveNumber - 8 bits - ignored\r
	53	CurrentHead: .byte 0 # Current Head - 8 bits\r
	54	Signature: .byte 0 # Signature - 8 bits - ignored\r
	55	VolId: .ascii " " # Volume Serial Number- 4 bytes\r
	56	FatLabel: .ascii " " # Label - 11 bytes\r
	57	SystemId: .ascii "FAT12 " # SystemId - 8 bytes\r
	58	\r
	59	BootSectorEntryPoint: \r
	60	#ASSUME ds:@code\r
	61	#ASSUME ss:@code\r
	62	\r
	63	# ****************************************************************************\r
	64	# Start Print\r
65	# ****************************************************************************\r
66	leaw %cs:StartString, %si\r
67	call PrintString\r
68	\r
69	# ****************************************************************************\r
70	# Print over\r
71	# ****************************************************************************\r
72	\r
73	movw %cs, %ax # ax = 0\r
74	movw %ax, %ss # ss = 0\r
75	addw $0x1000, %ax\r
76	movw %ax, %ds\r
77	\r
78	movw $0x7c00, %sp # sp = 0x7c00\r
79	movw %sp, %bp # bp = 0x7c00\r
80	\r
81	movb $8, %ah # ah = 8 - Get Drive Parameters Function\r
82	movb %dl, PhysicalDrive(%bp) # BBS defines that BIOS would pass the booting driver number to the loader through DL\r
83	int $0x13 # Get Drive Parameters\r
84	xorw %ax, %ax # ax = 0\r
85	movb %dh, %al # al = dh\r
86	incb %al # MaxHead = al + 1\r
87	pushw %ax # 0000:7bfe = MaxHead\r
88	movb %cl, %al # al = cl\r
89	andb $0x3f, %al # MaxSector = al & 0x3f\r
90	pushw %ax # 0000:7bfc = MaxSector\r
91	\r
92	cmpw $0xaa55, SectorSignature(%bp) # Verify Boot Sector Signature\r
93	jne BadBootSector\r
94	movw RootEntries(%bp), %cx # cx = RootEntries\r
95	shlw $FAT_DIRECTORY_ENTRY_SHIFT, %cx # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes\r
96	movw %cx, %bx # bx = size of the Root Directory in bytes\r
97	andw $BLOCK_MASK, %bx # See if it is an even number of sectors long\r
98	jne BadBootSector # If is isn't, then the boot sector is bad.\r
99	movw %cx, %bx # bx = size of the Root Directory in bytes\r
100	shrw $BLOCK_SHIFT, %bx # bx = size of Root Directory in sectors\r
101	movb NoFats(%bp), %al # al = NoFats\r
102	xorb %ah, %ah # ah = 0 ==> ax = NoFats\r
103	mulw SectorsPerFat(%bp) # ax = NoFats * SectorsPerFat\r
104	addw ReservedSectors(%bp), %ax # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA\r
105	pushw %ds\r
106	popw %es\r
107	xorw %di, %di # Store directory in es:di = 1000:0000\r
108	call ReadBlocks # Read entire Root Directory\r
109	addw %bx, %ax # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector)\r
110	movw %ax, (%bp) # Save FirstClusterLBA (FirstDataSector) for later use\r
111	\r
112	# dx - variable storage (initial value is 0)\r
113	# bx - loader (initial value is 0)\r
114	xorw %dx, %dx\r
115	xorw %bx, %bx\r
116	\r
117	FindEFILDR: \r
118	cmpl $LOADER_FILENAME_PART1, (%di) # Compare to "EFIL"\r
119	jne FindVARSTORE\r
120	cmpl $LOADER_FILENAME_PART2, 4(%di) \r
121	jne FindVARSTORE\r
122	cmpl $LOADER_FILENAME_PART3, 7(%di) \r
123	jne FindVARSTORE\r
124	movw 26(%di), %bx # bx = Start Cluster for EFILDR <----------------------------------\r
125	testw %dx, %dx\r
126	je FindNext # Efivar.bin is not loaded\r
127	jmp FoundAll\r
128	\r
129	FindVARSTORE: \r
130	## if the file is not loader file, see if it's "EFIVAR BIN"\r
131	cmpl $0x56494645, (%di) # Compare to "EFIV"\r
132	jne FindNext\r
133	cmpl $0x20205241, 4(%di) # Compare to "AR "\r
134	jne FindNext\r
135	cmpl $0x4e494220, 7(%di) # Compare to " BIN"\r
136	jne FindNext\r
137	movw %di, %dx # dx = Offset of Start Cluster for Efivar.bin <---------------------\r
138	addw $26, %dx\r
139	testw %bx, %bx\r
140	je FindNext # Efildr is not loaded\r
141	jmp FoundAll\r
142	\r
143	FindNext: \r
144	# go to next find\r
145	addw $FAT_DIRECTORY_ENTRY_SIZE, %di # Increment di\r
146	subw $FAT_DIRECTORY_ENTRY_SIZE, %cx # Decrement cx\r
147	# TODO: jump to FindVarStore if ...\r
148	jne FindEFILDR\r
149	jmp NotFoundAll\r
150	\r
151	FoundAll: \r
152	FoundEFILDR: \r
153	movw %bx, %cx # cx = Start Cluster for EFILDR <----------------------------------\r
154	movw %cs, %ax # Destination = 2000:0000\r
155	addw $0x2000, %ax\r
156	movw %ax, %es\r
157	xorw %di, %di\r
158	ReadFirstClusterOfEFILDR: \r
159	movw %cx, %ax # ax = StartCluster\r
160	subw $2, %ax # ax = StartCluster - 2\r
161	xorb %bh, %bh\r
162	movb SectorsPerCluster(%bp), %bl # bx = SectorsPerCluster\r
163	pushw %dx\r
164	mulw %bx\r
165	popw %dx # ax = (StartCluster - 2) * SectorsPerCluster\r
166	addw (%bp), %ax # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster\r
167	xorb %bh, %bh\r
168	movb SectorsPerCluster(%bp), %bl # bx = Number of Sectors in a cluster\r
169	pushw %es\r
170	call ReadBlocks\r
171	popw %ax\r
172	JumpIntoFirstSectorOfEFILDR: \r
173	movw %ax, JumpSegment(%bp)\r
174	JumpFarInstruction: \r
175	.byte 0xea\r
176	JumpOffset: \r
177	.word 0x000\r
178	JumpSegment: \r
179	.word 0x2000\r
180	\r
181	\r
182	PrintString: \r
183	movw $0xb800, %ax\r
184	movw %ax, %es\r
185	movw $0x7c0, %ax\r
186	movw %ax, %ds\r
187	movw $7, %cx\r
188	movw $160, %di\r
189	rep\r
190	movsw\r
191	ret\r
192	# ****************************************************************************\r
193	# ReadBlocks - Reads a set of blocks from a block device\r
194	#\r
195	# AX = Start LBA\r
196	# BX = Number of Blocks to Read\r
197	# ES:DI = Buffer to store sectors read from disk\r
198	# ****************************************************************************\r
199	\r
200	# cx = Blocks\r
201	# bx = NumberOfBlocks\r
202	# si = StartLBA\r
203	\r
204	ReadBlocks: \r
205	pusha\r
206	addl LBAOffsetForBootSector(%bp), %eax # Add LBAOffsetForBootSector to Start LBA\r
207	addl HiddenSectors(%bp), %eax # Add HiddenSectors to Start LBA\r
208	movl %eax, %esi # esi = Start LBA\r
209	movw %bx, %cx # cx = Number of blocks to read\r
210	ReadCylinderLoop: \r
211	movw $0x7bfc, %bp # bp = 0x7bfc\r
212	movl %esi, %eax # eax = Start LBA\r
213	xorl %edx, %edx # edx = 0\r
214	movzwl (%bp), %ebx # bx = MaxSector\r
215	divl %ebx # ax = StartLBA / MaxSector\r
216	incw %dx # dx = (StartLBA % MaxSector) + 1\r
217	subw %dx, %bx # bx = MaxSector - Sector\r
218	incw %bx # bx = MaxSector - Sector + 1\r
219	cmpw %bx, %cx # Compare (Blocks) to (MaxSector - Sector + 1)\r
220	jg LimitTransfer\r
221	movw %cx, %bx # bx = Blocks\r
222	LimitTransfer: \r
223	pushw %cx\r
224	movb %dl, %cl # cl = (StartLBA % MaxSector) + 1 = Sector\r
225	xorw %dx, %dx # dx = 0\r
226	divw 2(%bp) # ax = ax / (MaxHead + 1) = Cylinder \r
227	# dx = ax % (MaxHead + 1) = Head\r
228	\r
229	pushw %bx # Save number of blocks to transfer\r
230	movb %dl, %dh # dh = Head\r
231	movw $0x7c00, %bp # bp = 0x7c00\r
232	movb PhysicalDrive(%bp), %dl # dl = Drive Number\r
233	movb %al, %ch # ch = Cylinder\r
234	movb %bl, %al # al = Blocks\r
235	movb $2, %ah # ah = Function 2\r
236	movw %di, %bx # es:bx = Buffer address\r
237	int $0x13\r
238	jc DiskError\r
239	popw %bx\r
240	popw %cx\r
241	movzwl %bx, %ebx\r
242	addl %ebx, %esi # StartLBA = StartLBA + NumberOfBlocks\r
243	subw %bx, %cx # Blocks = Blocks - NumberOfBlocks\r
244	movw %es, %ax\r
245	shlw $(BLOCK_SHIFT-4), %bx\r
246	addw %bx, %ax\r
247	movw %ax, %es # es:di = es:di + NumberOfBlocks*BLOCK_SIZE\r
248	cmpw $0, %cx\r
249	jne ReadCylinderLoop\r
250	popa\r
251	ret\r
252	\r
253	# ****************************************************************************\r
254	# ERROR Condition:\r
255	# ****************************************************************************\r
256	NotFoundAll: \r
257	## if we found EFILDR, continue\r
258	testw %bx, %bx\r
259	jne FoundEFILDR\r
260	BadBootSector: \r
261	DiskError: \r
262	leaw %cs:ErrorString, %si\r
263	call PrintString\r
264	Halt: \r
265	jmp Halt\r
266	\r
267	StartString: \r
268	.byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c\r
269	ErrorString: \r
270	.byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c\r
271	\r
272	# ****************************************************************************\r
273	# LBA Offset for BootSector, need patched by tool for HD boot.\r
274	# ****************************************************************************\r
275	\r
276	# .org 0x01fa # Comment it for pass build. Should optimise code size. \r
277	LBAOffsetForBootSector: \r
278	.long 0x0\r
279	\r
280	# ****************************************************************************\r
281	# Sector Signature\r
282	# ****************************************************************************\r
283	\r
284	# .org 0x01fe # Comment it for pass build.\r
285	SectorSignature: \r
286	.word 0xaa55 # Boot Sector Signature\r
287	\r
288	\r
289	\r