1#------------------------------------------------------------------------------
2#*
3#*   Copyright (c) 2006 - 2012, 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#*    bs32.asm
13#*
14#*   Abstract:
15#*
16#------------------------------------------------------------------------------
17
18        #.MODEL small
19        .stack:
20        .486p:
21        .code16
22
23.equ                      FAT_DIRECTORY_ENTRY_SIZE, 0x0020
24.equ                      FAT_DIRECTORY_ENTRY_SHIFT, 5
25.equ                      BLOCK_SIZE, 0x0200
26.equ                      BLOCK_MASK, 0x01ff
27.equ                      BLOCK_SHIFT, 9
28                                               # "EFILDR_____"
29.equ                      LOADER_FILENAME_PART1, 0x4c494645    # "EFIL"
30.equ                      LOADER_FILENAME_PART2, 0x30325244    # "DR20"
31.equ                      LOADER_FILENAME_PART3, 0x20202030    # "0___"
32
33        .org 0x0
34.global _start
35_start:
36Ia32Jump:
37  jmp   BootSectorEntryPoint  # JMP inst                  - 3 bytes
38  nop
39
40OemId:             .ascii  "INTEL   "   # OemId               - 8 bytes
41# BPB data below will be fixed by tool
42SectorSize:        .word  0             # Sector Size         - 16 bits
43SectorsPerCluster: .byte  0             # Sector Per Cluster  - 8 bits
44ReservedSectors:   .word  0             # Reserved Sectors    - 16 bits
45NoFats:            .byte  0             # Number of FATs      - 8 bits
46RootEntries:       .word  0             # Root Entries        - 16 bits
47Sectors:           .word  0             # Number of Sectors   - 16 bits
48Media:             .byte  0             # Media               - 8 bits  - ignored
49SectorsPerFat:     .word  0             # Sectors Per FAT     - 16 bits
50SectorsPerTrack:   .word  0             # Sectors Per Track   - 16 bits - ignored
51Heads:             .word  0             # Heads               - 16 bits - ignored
52HiddenSectors:     .long  0             # Hidden Sectors      - 32 bits - ignored
53LargeSectors:      .long  0             # Large Sectors       - 32 bits
54
55#******************************************************************************
56#
57#The structure for FAT32 starting at offset 36 of the boot sector. (At this point,
58#the BPB/boot sector for FAT12 and FAT16 differs from the BPB/boot sector for FAT32.)
59#
60#******************************************************************************
61
62SectorsPerFat32:   .long  0              # Sectors Per FAT for FAT32       - 4 bytes
63ExtFlags:          .word  0              # Mirror Flag                     - 2 bytes
64FSVersion:         .word  0              # File System Version             - 2 bytes
65RootCluster:       .long  0              # 1st Cluster Number of Root Dir  - 4 bytes
66FSInfo:            .word  0              # Sector Number of FSINFO         - 2 bytes
67BkBootSector:      .word  0              # Sector Number of Bk BootSector  - 2 bytes
68Reserved:          .fill  12, 1, 0       # Reserved Field                  - 12 bytes
69PhysicalDrive:     .byte  0              # Physical Drive Number           - 1 byte
70Reserved1:         .byte  0              # Reserved Field                  - 1 byte
71Signature:         .byte  0              # Extended Boot Signature         - 1 byte
72VolId:             .ascii  "    "        # Volume Serial Number            - 4 bytes
73FatLabel:          .ascii  "           " # Volume Label                    - 11 bytes
74FileSystemType:    .ascii  "FAT32   "    # File System Type                - 8 bytes
75BootSectorEntryPoint:
76        #ASSUME ds:@code
77        #ASSUME ss:@code
78
79# ****************************************************************************
80# Start Print
81# ****************************************************************************
82  movw $StartString, %si
83  call PrintString
84
85# ****************************************************************************
86# Print over
87# ****************************************************************************
88
89  movw  %cs, %ax      # ax = 0
90  movw  %ax, %ss      # ss = 0
91  addw  $0x1000, %ax
92  movw  %ax, %ds
93
94  movw  $0x7c00, %sp  # sp = 0x7c00
95  movw  %sp, %bp      # bp = 0x7c00
96
97  movb  $8, %ah                             # ah = 8 - Get Drive Parameters Function
98  movb  %dl, PhysicalDrive(%bp)             # BBS defines that BIOS would pass the booting driver number to the loader through DL
99  int   $0x13                               # Get Drive Parameters
100  xorw  %ax, %ax                # ax = 0
101  movb  %dh, %al                # al = dh
102  incb  %al                     # MaxHead = al + 1
103  pushw %ax                     # 0000:7bfe = MaxHead
104  movb  %cl, %al                # al = cl
105  andb  $0x3f, %al              # MaxSector = al & 0x3f
106  pushw %ax                     # 0000:7bfc = MaxSector
107
108  cmpw  $0xaa55, SectorSignature(%bp)         # Verify Boot Sector Signature
109  jne   BadBootSector
110  movw  RootEntries(%bp), %cx             # cx = RootEntries
111  shlw  $FAT_DIRECTORY_ENTRY_SHIFT, %cx   # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes
112  movw  %cx, %bx                          # bx = size of the Root Directory in bytes
113  andw  $BLOCK_MASK, %bx                  # See if it is an even number of sectors long
114  jne   BadBootSector                     # If is isn't, then the boot sector is bad.
115  movw  %cx, %bx                          # bx = size of the Root Directory in bytes
116  shrw  $BLOCK_SHIFT, %bx                 # bx = size of Root Directory in sectors
117  movb  NoFats(%bp), %al                  # al = NoFats
118  xorb  %ah, %ah                          # ah = 0  ==> ax = NoFats
119  mulw  SectorsPerFat32(%bp)              # ax = NoFats * SectorsPerFat
120  addw  ReservedSectors(%bp), %ax         # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA
121  addw  %bx, %ax                          # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA
122  movw  %ax, (%bp)                        # Save FirstClusterLBA for later use
123
124  movw  RootCluster(%bp), %ax             # ax = StartCluster of Root Directory
125  subw  $2, %ax                           # ax = StartCluster - 2
126  xorb  %bh, %bh
127  movb  SectorsPerCluster(%bp), %bl       # bx = SectorsPerCluster
128  mulw  %bx                               # ax = (StartCluster - 2) * SectorsPerCluster
129  addw  (%bp), %ax                        # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster
130  pushw %ds
131  popw  %es
132  xorw  %di, %di                          # Store directory in es:di = 1000:0000
133  call  ReadBlocks                        # Read StartCluster of Root Directory
134
135  # dx - variable storage (initial value is 0)
136  # bx - loader (initial value is 0)
137  xorw  %dx, %dx
138  xorw  %bx, %bx
139
140FindEFILDR:
141  cmpl  $LOADER_FILENAME_PART1, (%di)
142  jne   FindVARSTORE
143  cmpl  $LOADER_FILENAME_PART2, 4(%di)
144  jne   FindVARSTORE
145  cmpl  $LOADER_FILENAME_PART3, 7(%di)
146  jne   FindVARSTORE
147  movw  26(%di), %bx                      # bx = Start Cluster for EFILDR  <----------------------------------
148  testw %dx, %dx
149  je    FindNext                          # Efivar.bin is not loaded
150  jmp   FoundAll
151
152FindVARSTORE:
153  ## if the file is not loader file, see if it's "EFIVAR  BIN"
154  cmpl  $0x56494645, (%di)                # Compare to "EFIV"
155  jne   FindNext
156  cmpl  $0x20205241, 4(%di)               # Compare to "AR  "
157  jne   FindNext
158  cmpl  $0x4e494220, 7(%di)               # Compare to " BIN"
159  jne   FindNext
160  movw  %di, %dx                          # dx = Offset of Start Cluster for Efivar.bin <---------------------
161  addw  $26, %dx
162  testw %bx, %bx
163  je    FindNext                          # Efildr is not loaded
164  jmp   FoundAll
165
166FindNext:
167  # go to next find
168  addw  $FAT_DIRECTORY_ENTRY_SIZE, %di    # Increment di
169  subw  $FAT_DIRECTORY_ENTRY_SIZE, %cx    # Decrement cx
170  # TODO: jump to FindVarStore if ...
171  jne   FindEFILDR
172  jmp   NotFoundAll
173
174FoundAll:
175FoundEFILDR:
176  movw    %bx, %cx                            # cx = Start Cluster for EFILDR  <----------------------------------
177  movw    %cs, %ax                            # Destination = 2000:0000
178  addw    $0x2000, %ax
179  movw    %ax, %es
180  xorw    %di, %di
181ReadFirstClusterOfEFILDR:
182  movw    %cx, %ax                            # ax = StartCluster
183  subw    $2, %ax                             # ax = StartCluster - 2
184  xorb    %bh, %bh
185  movb    SectorsPerCluster(%bp), %bl         # bx = SectorsPerCluster
186  pushw   %dx
187  mulw    %bx
188  popw    %dx                                 # ax = (StartCluster - 2) * SectorsPerCluster
189  addw    (%bp), %ax                          # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster
190  xorb    %bh, %bh
191  movb    SectorsPerCluster(%bp), %bl         # bx = Number of Sectors in a cluster
192  pushw   %es
193  call    ReadBlocks
194  popw    %ax
195JumpIntoFirstSectorOfEFILDR:
196  movw    %ax, JumpSegment(%bp)
197JumpFarInstruction:
198  .byte   0xea
199JumpOffset:
200  .word   0x000
201JumpSegment:
202  .word   0x2000
203
204
205PrintString:
206  movw $0xb800, %ax
207  movw %ax, %es
208  movw $0x7c0, %ax
209  movw %ax, %ds
210  movw $6, %cx
211  movw $160, %di
212  rep
213  movsw
214  ret
215# ****************************************************************************
216# ReadBlocks - Reads a set of blocks from a block device
217#
218# AX    = Start LBA
219# BX    = Number of Blocks to Read
220# ES:DI = Buffer to store sectors read from disk
221# ****************************************************************************
222
223# cx = Blocks
224# bx = NumberOfBlocks
225# si = StartLBA
226
227ReadBlocks:
228  pusha
229  addl    LBAOffsetForBootSector(%bp), %eax            # Add LBAOffsetForBootSector to Start LBA
230  addl    HiddenSectors(%bp), %eax            # Add HiddenSectors to Start LBA
231  movl    %eax, %esi                          # esi = Start LBA
232  movw    %bx, %cx                            # cx = Number of blocks to read
233ReadCylinderLoop:
234  movw    $0x7bfc, %bp                        # bp = 0x7bfc
235  movl    %esi, %eax                          # eax = Start LBA
236  xorl    %edx, %edx                          # edx = 0
237  movzwl  (%bp), %ebx                         # bx = MaxSector
238  divl    %ebx                                # ax = StartLBA / MaxSector
239  incw    %dx                                 # dx = (StartLBA % MaxSector) + 1
240  subw    %dx, %bx                            # bx = MaxSector - Sector
241  incw    %bx                                 # bx = MaxSector - Sector + 1
242  cmpw    %bx, %cx                            # Compare (Blocks) to (MaxSector - Sector + 1)
243  jg      LimitTransfer
244  movw    %cx, %bx                            # bx = Blocks
245LimitTransfer:
246  pushw   %cx
247  movb    %dl, %cl                            # cl = (StartLBA % MaxSector) + 1 = Sector
248  xorw    %dx, %dx                            # dx = 0
249  divw    2(%bp)                              # ax = ax / (MaxHead + 1) = Cylinder
250                                              # dx = ax % (MaxHead + 1) = Head
251
252  pushw   %bx                                 # Save number of blocks to transfer
253  movb    %dl, %dh                            # dh = Head
254  movw    $0x7c00, %bp                        # bp = 0x7c00
255  movb    PhysicalDrive(%bp), %dl             # dl = Drive Number
256  movb    %al, %ch                            # ch = Cylinder
257  movb    %bl, %al                            # al = Blocks
258  movb    $2, %ah                             # ah = Function 2
259  movw    %di, %bx                            # es:bx = Buffer address
260  int     $0x13
261  jc      DiskError
262  popw    %bx
263  popw    %cx
264  movzwl  %bx, %ebx
265  addl    %ebx, %esi                          # StartLBA = StartLBA + NumberOfBlocks
266  subw    %bx, %cx                            # Blocks = Blocks - NumberOfBlocks
267  movw    %es, %ax
268  shlw    $(BLOCK_SHIFT-4), %bx
269  addw    %bx, %ax
270  movw    %ax, %es                            # es:di = es:di + NumberOfBlocks*BLOCK_SIZE
271  cmpw    $0, %cx
272  jne     ReadCylinderLoop
273  popa
274  ret
275
276# ****************************************************************************
277# ERROR Condition:
278# ****************************************************************************
279NotFoundAll:
280  ## if we found EFILDR, continue
281  testw %bx, %bx
282  jne  FoundEFILDR
283BadBootSector:
284DiskError:
285  movw $ErrorString, %si
286  call PrintString
287Halt:
288  jmp   Halt
289
290StartString:
291  .byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c
292ErrorString:
293  .byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c
294
295# ****************************************************************************
296# LBA Offset for BootSector, need patched by tool for HD boot.
297# ****************************************************************************
298
299  .org 0x01fa
300LBAOffsetForBootSector:
301  .long     0x0
302
303# ****************************************************************************
304# Sector Signature
305# ****************************************************************************
306
307  .org 0x01fe
308SectorSignature:
309  .word     0xaa55      # Boot Sector Signature
310
311
312
313