1#------------------------------------------------------------------------------
2#*
3#*   Copyright (c) 2006 - 2007, Intel Corporation. All rights reserved.<BR>
4#*   This program and the accompanying materials
5#*   are licensed and made available under the terms and conditions of the BSD License
6#*   which accompanies this distribution.  The full text of the license may be found at
7#*   http://opensource.org/licenses/bsd-license.php
8#*
9#*   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
10#*   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
11#*
12#*   bootsect.S
13#*
14#*   bootsect.S is built as 16-bit binary file in 512 bytes and patched to disk/partition's
15#*   first section - boot sector.
16#*
17#*   The startup sequence for DUET disk boot sector is:
18#*
19#*   1, LegacyBios check 0xAA55 signature at boot sectore offset 0x1FE to judget
20#*      whether disk/partition is bootable.
21#*   2, LegacyBios will load boot sector to 0x7c00 in real mode, pass BPB data and
22#*      hand off control to 0x7c00 code.
23#*   3, boot sector code simply parse FAT format in boot disk and find EfiLdr binary file
24#*      and EfiVar.bin if exists. For first boot, EfiVar.bin does not exist.
25#*   4, boot sector load the first sector of EfiLdr binary which is start.com to
26#*      0x2000:0x0000 address.
27#*   5, boot sector handoff control to 0x2000:0x0000 for start.com binary.
28#*
29#------------------------------------------------------------------------------
30
31        .stack:
32        .486p:
33        .code16
34
35.equ                      FAT_DIRECTORY_ENTRY_SIZE, 0x020
36.equ                      FAT_DIRECTORY_ENTRY_SHIFT, 5
37.equ                      BLOCK_SIZE, 0x0200
38.equ                      BLOCK_MASK, 0x01ff
39.equ                      BLOCK_SHIFT, 9
40                                               # "EFILDR_____"
41.equ                      LOADER_FILENAME_PART1, 0x04c494645    # "EFIL"
42.equ                      LOADER_FILENAME_PART2, 0x020205244    # "DR__"
43.equ                      LOADER_FILENAME_PART3, 0x020202020    # "____"
44
45        .org 0x0
46.global _start
47_start:
48Ia32Jump:
49  jmp   BootSectorEntryPoint  # JMP inst                  - 3 bytes
50  nop
51
52OemId:              .ascii   "INTEL   "       # OemId               - 8 bytes
53# BPB data below will be fixed by tool
54SectorSize:         .word  0                  # Sector Size         - 16 bits
55SectorsPerCluster:  .byte  0                  # Sector Per Cluster  - 8 bits
56ReservedSectors:    .word  0                  # Reserved Sectors    - 16 bits
57NoFats:             .byte  0                  # Number of FATs      - 8 bits
58RootEntries:        .word  0                  # Root Entries        - 16 bits
59Sectors:            .word  0                  # Number of Sectors   - 16 bits
60Media:              .byte  0                  # Media               - 8 bits  - ignored
61SectorsPerFat:      .word  0                  # Sectors Per FAT     - 16 bits
62SectorsPerTrack:    .word  0                  # Sectors Per Track   - 16 bits - ignored
63Heads:              .word  0                  # Heads               - 16 bits - ignored
64HiddenSectors:      .long  0                  # Hidden Sectors      - 32 bits - ignored
65LargeSectors:       .long  0                  # Large Sectors       - 32 bits
66PhysicalDrive:      .byte  0                  # PhysicalDriveNumber - 8 bits  - ignored
67CurrentHead:        .byte  0                  # Current Head        - 8 bits
68Signature:          .byte  0                  # Signature           - 8 bits  - ignored
69VolId:              .ascii "    "             # Volume Serial Number- 4 bytes
70FatLabel:           .ascii "           "      # Label               - 11 bytes
71SystemId:           .ascii "FAT12   "         # SystemId            - 8 bytes
72
73BootSectorEntryPoint:
74        #ASSUME ds:@code
75        #ASSUME ss:@code
76
77# ****************************************************************************
78# Start Print
79# ****************************************************************************
80  movw $StartString, %si
81  call PrintString
82
83# ****************************************************************************
84# Print over
85# ****************************************************************************
86
87  movw  %cs, %ax      # ax = 0
88  movw  %ax, %ss      # ss = 0
89  addw  $0x1000, %ax
90  movw  %ax, %ds
91
92  movw  $0x7c00, %sp  # sp = 0x7c00
93  movw  %sp, %bp      # bp = 0x7c00
94
95  movb  $8, %ah                             # ah = 8 - Get Drive Parameters Function
96  movb  %dl, PhysicalDrive(%bp)             # BBS defines that BIOS would pass the booting driver number to the loader through DL
97  int   $0x13                               # Get Drive Parameters
98  xorw  %ax, %ax                # ax = 0
99  movb  %dh, %al                # al = dh
100  incb  %al                     # MaxHead = al + 1
101  pushw %ax                     # 0000:7bfe = MaxHead
102  movb  %cl, %al                # al = cl
103  andb  $0x3f, %al              # MaxSector = al & 0x3f
104  pushw %ax                     # 0000:7bfc = MaxSector
105
106  cmpw  $0xaa55, SectorSignature(%bp)         # Verify Boot Sector Signature
107  jne   BadBootSector
108  movw  RootEntries(%bp), %cx             # cx = RootEntries
109  shlw  $FAT_DIRECTORY_ENTRY_SHIFT, %cx   # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes
110  movw  %cx, %bx                          # bx = size of the Root Directory in bytes
111  andw  $BLOCK_MASK, %bx                  # See if it is an even number of sectors long
112  jne   BadBootSector                     # If is isn't, then the boot sector is bad.
113  movw  %cx, %bx                          # bx = size of the Root Directory in bytes
114  shrw  $BLOCK_SHIFT, %bx                 # bx = size of Root Directory in sectors
115  movb  NoFats(%bp), %al                  # al = NoFats
116  xorb  %ah, %ah                          # ah = 0  ==> ax = NoFats
117  mulw  SectorsPerFat(%bp)                # ax = NoFats * SectorsPerFat
118  addw  ReservedSectors(%bp), %ax         # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA
119  pushw %ds
120  popw  %es
121  xorw  %di, %di                          # Store directory in es:di = 1000:0000
122  call  ReadBlocks                        # Read entire Root Directory
123  addw  %bx, %ax                          # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector)
124  movw  %ax, (%bp)                        # Save FirstClusterLBA (FirstDataSector) for later use
125
126  # dx - variable storage (initial value is 0)
127  # bx - loader (initial value is 0)
128  xorw  %dx, %dx
129  xorw  %bx, %bx
130
131FindEFILDR:
132  cmpl   $LOADER_FILENAME_PART1, (%di)        # Compare to "EFIL"
133  jne   FindVARSTORE
134  cmpl   $LOADER_FILENAME_PART2, 4(%di)
135  jne   FindVARSTORE
136  cmpl   $LOADER_FILENAME_PART3, 7(%di)
137  jne   FindVARSTORE
138  movw  26(%di), %bx                      # bx = Start Cluster for EFILDR  <----------------------------------
139  testw %dx, %dx
140  je    FindNext                          # Efivar.bin is not loaded
141  jmp   FoundAll
142
143FindVARSTORE:
144  ## if the file is not loader file, see if it's "EFIVAR  BIN"
145  cmpl  $0x56494645, (%di)                # Compare to "EFIV"
146  jne   FindNext
147  cmpl  $0x20205241, 4(%di)               # Compare to "AR  "
148  jne   FindNext
149  cmpl  $0x4e494220, 7(%di)               # Compare to " BIN"
150  jne   FindNext
151  movw  %di, %dx                          # dx = Offset of Start Cluster for Efivar.bin <---------------------
152  addw  $26, %dx
153  testw %bx, %bx
154  je    FindNext                          # Efildr is not loaded
155  jmp   FoundAll
156
157FindNext:
158  # go to next find
159  addw  $FAT_DIRECTORY_ENTRY_SIZE, %di    # Increment di
160  subw  $FAT_DIRECTORY_ENTRY_SIZE, %cx    # Decrement cx
161  # TODO: jump to FindVarStore if ...
162  jne   FindEFILDR
163  jmp   NotFoundAll
164
165FoundAll:
166FoundEFILDR:
167  movw    %bx, %cx                            # cx = Start Cluster for EFILDR  <----------------------------------
168  movw    %cs, %ax                            # Destination = 2000:0000
169  addw    $0x2000, %ax
170  movw    %ax, %es
171  xorw    %di, %di
172ReadFirstClusterOfEFILDR:
173  movw    %cx, %ax                            # ax = StartCluster
174  subw    $2, %ax                             # ax = StartCluster - 2
175  xorb    %bh, %bh
176  movb    SectorsPerCluster(%bp), %bl         # bx = SectorsPerCluster
177  pushw   %dx
178  mulw    %bx
179  popw    %dx                                 # ax = (StartCluster - 2) * SectorsPerCluster
180  addw    (%bp), %ax                          # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster
181  xorb    %bh, %bh
182  movb    SectorsPerCluster(%bp), %bl         # bx = Number of Sectors in a cluster
183  pushw   %es
184  call    ReadBlocks
185  popw    %ax
186JumpIntoFirstSectorOfEFILDR:
187  movw    %ax, JumpSegment(%bp)
188JumpFarInstruction:
189  .byte   0xea
190JumpOffset:
191  .word   0x000
192JumpSegment:
193  .word   0x2000
194
195
196PrintString:
197  movw $0xb800, %ax
198  movw %ax, %es
199  movw $0x7c0, %ax
200  movw %ax, %ds
201  movw $7, %cx
202  movw $160, %di
203  rep
204  movsw
205  ret
206# ****************************************************************************
207# ReadBlocks - Reads a set of blocks from a block device
208#
209# AX    = Start LBA
210# BX    = Number of Blocks to Read
211# ES:DI = Buffer to store sectors read from disk
212# ****************************************************************************
213
214# cx = Blocks
215# bx = NumberOfBlocks
216# si = StartLBA
217
218ReadBlocks:
219  pusha
220  addl    LBAOffsetForBootSector(%bp), %eax            # Add LBAOffsetForBootSector to Start LBA
221  addl    HiddenSectors(%bp), %eax            # Add HiddenSectors to Start LBA
222  movl    %eax, %esi                          # esi = Start LBA
223  movw    %bx, %cx                            # cx = Number of blocks to read
224ReadCylinderLoop:
225  movw    $0x7bfc, %bp                        # bp = 0x7bfc
226  movl    %esi, %eax                          # eax = Start LBA
227  xorl    %edx, %edx                          # edx = 0
228  movzwl  (%bp), %ebx                         # bx = MaxSector
229  divl    %ebx                                # ax = StartLBA / MaxSector
230  incw    %dx                                 # dx = (StartLBA % MaxSector) + 1
231  subw    %dx, %bx                            # bx = MaxSector - Sector
232  incw    %bx                                 # bx = MaxSector - Sector + 1
233  cmpw    %bx, %cx                            # Compare (Blocks) to (MaxSector - Sector + 1)
234  jg      LimitTransfer
235  movw    %cx, %bx                            # bx = Blocks
236LimitTransfer:
237  pushw   %cx
238  movb    %dl, %cl                            # cl = (StartLBA % MaxSector) + 1 = Sector
239  xorw    %dx, %dx                            # dx = 0
240  divw    2(%bp)                              # ax = ax / (MaxHead + 1) = Cylinder
241                                              # dx = ax % (MaxHead + 1) = Head
242
243  pushw   %bx                                 # Save number of blocks to transfer
244  movb    %dl, %dh                            # dh = Head
245  movw    $0x7c00, %bp                        # bp = 0x7c00
246  movb    PhysicalDrive(%bp), %dl             # dl = Drive Number
247  movb    %al, %ch                            # ch = Cylinder
248  movb    %bl, %al                            # al = Blocks
249  movb    $2, %ah                             # ah = Function 2
250  movw    %di, %bx                            # es:bx = Buffer address
251  int     $0x13
252  jc      DiskError
253  popw    %bx
254  popw    %cx
255  movzwl  %bx, %ebx
256  addl    %ebx, %esi                          # StartLBA = StartLBA + NumberOfBlocks
257  subw    %bx, %cx                            # Blocks = Blocks - NumberOfBlocks
258  movw    %es, %ax
259  shlw    $(BLOCK_SHIFT-4), %bx
260  addw    %bx, %ax
261  movw    %ax, %es                            # es:di = es:di + NumberOfBlocks*BLOCK_SIZE
262  cmpw    $0, %cx
263  jne     ReadCylinderLoop
264  popa
265  ret
266
267# ****************************************************************************
268# ERROR Condition:
269# ****************************************************************************
270NotFoundAll:
271  ## if we found EFILDR, continue
272  testw %bx, %bx
273  jne  FoundEFILDR
274BadBootSector:
275DiskError:
276  movw $ErrorString, %si
277  call PrintString
278Halt:
279  jmp   Halt
280
281StartString:
282  .byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c
283ErrorString:
284  .byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c
285
286# ****************************************************************************
287# LBA Offset for BootSector, need patched by tool for HD boot.
288# ****************************************************************************
289
290  .org 0x01fa   # Comment it for pass build. Should optimise code size.
291LBAOffsetForBootSector:
292  .long     0x0
293
294# ****************************************************************************
295# Sector Signature
296# ****************************************************************************
297
298  .org 0x01fe    # Comment it for pass build.
299SectorSignature:
300  .word     0xaa55      # Boot Sector Signature
301
302
303
304