| blob | cbb3649a46a9e359059339d9c7746d6b30716adf |
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 #* bs16.asm\r
13 #* \r
14 #* Abstract:\r
15 #*\r
16 #------------------------------------------------------------------------------\r
17 \r
18 #.MODEL small\r
19 .stack: \r
20 .486p: \r
21 .code16\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, 0x036315244 # "DR16"\r
31 .equ LOADER_FILENAME_PART3, 0x020202036 # "6___"\r
32 \r
33 .org 0x0\r
35 _start:\r
36 Ia32Jump: \r
37 jmp BootSectorEntryPoint # JMP inst - 3 bytes\r
38 nop\r
39 \r
40 OemId: .ascii "INTEL " # OemId - 8 bytes\r
41 # BPB data below will be fixed by tool\r
42 SectorSize: .word 0 # Sector Size - 16 bits\r
43 SectorsPerCluster: .byte 0 # Sector Per Cluster - 8 bits\r
44 ReservedSectors: .word 0 # Reserved Sectors - 16 bits\r
45 NoFats: .byte 0 # Number of FATs - 8 bits\r
46 RootEntries: .word 0 # Root Entries - 16 bits\r
47 Sectors: .word 0 # Number of Sectors - 16 bits\r
48 Media: .byte 0 # Media - 8 bits - ignored\r
49 SectorsPerFat: .word 0 # Sectors Per FAT - 16 bits\r
50 SectorsPerTrack: .word 0 # Sectors Per Track - 16 bits - ignored\r
51 Heads: .word 0 # Heads - 16 bits - ignored\r
52 HiddenSectors: .long 0 # Hidden Sectors - 32 bits - ignored\r
53 LargeSectors: .long 0 # Large Sectors - 32 bits \r
54 PhysicalDrive: .byte 0 # PhysicalDriveNumber - 8 bits - ignored\r
55 CurrentHead: .byte 0 # Current Head - 8 bits\r
56 Signature: .byte 0 # Signature - 8 bits - ignored\r
57 VolId: .ascii " " # Volume Serial Number- 4 bytes\r
58 FatLabel: .ascii " " # Label - 11 bytes\r
59 SystemId: .ascii "FAT12 " # SystemId - 8 bytes\r
60 \r
61 BootSectorEntryPoint: \r
62 #ASSUME ds:@code\r
63 #ASSUME ss:@code\r
64 \r
65 # ****************************************************************************\r
66 # Start Print\r
67 # ****************************************************************************\r
68 movw $StartString, %si\r
69 call PrintString\r
70 \r
71 # ****************************************************************************\r
72 # Print over\r
73 # ****************************************************************************\r
74 \r
75 movw %cs, %ax # ax = 0\r
76 movw %ax, %ss # ss = 0\r
77 addw $0x1000, %ax\r
78 movw %ax, %ds\r
79 \r
80 movw $0x7c00, %sp # sp = 0x7c00\r
81 movw %sp, %bp # bp = 0x7c00\r
82 \r
83 movb $8, %ah # ah = 8 - Get Drive Parameters Function\r
84 movb %dl, PhysicalDrive(%bp) # BBS defines that BIOS would pass the booting driver number to the loader through DL\r
85 int $0x13 # Get Drive Parameters\r
86 xorw %ax, %ax # ax = 0\r
87 movb %dh, %al # al = dh\r
88 incb %al # MaxHead = al + 1\r
89 pushw %ax # 0000:7bfe = MaxHead\r
90 movb %cl, %al # al = cl\r
91 andb $0x3f, %al # MaxSector = al & 0x3f\r
92 pushw %ax # 0000:7bfc = MaxSector\r
93 \r
94 cmpw $0xaa55, SectorSignature(%bp) # Verify Boot Sector Signature\r
95 jne BadBootSector\r
96 movw RootEntries(%bp), %cx # cx = RootEntries\r
97 shlw $FAT_DIRECTORY_ENTRY_SHIFT, %cx # cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes\r
98 movw %cx, %bx # bx = size of the Root Directory in bytes\r
99 andw $BLOCK_MASK, %bx # See if it is an even number of sectors long\r
100 jne BadBootSector # If is isn't, then the boot sector is bad.\r
101 movw %cx, %bx # bx = size of the Root Directory in bytes\r
102 shrw $BLOCK_SHIFT, %bx # bx = size of Root Directory in sectors\r
103 movb NoFats(%bp), %al # al = NoFats\r
104 xorb %ah, %ah # ah = 0 ==> ax = NoFats\r
105 mulw SectorsPerFat(%bp) # ax = NoFats * SectorsPerFat\r
106 addw ReservedSectors(%bp), %ax # ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA\r
107 pushw %ds\r
108 popw %es\r
109 xorw %di, %di # Store directory in es:di = 1000:0000\r
110 call ReadBlocks # Read entire Root Directory\r
111 addw %bx, %ax # ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector)\r
112 movw %ax, (%bp) # Save FirstClusterLBA (FirstDataSector) for later use\r
113 \r
114 # dx - variable storage (initial value is 0)\r
115 # bx - loader (initial value is 0)\r
116 xorw %dx, %dx\r
117 xorw %bx, %bx\r
118 \r
119 FindEFILDR: \r
120 cmpl $LOADER_FILENAME_PART1, (%di) # Compare to "EFIL"\r
121 jne FindVARSTORE\r
122 cmpl $LOADER_FILENAME_PART2, 4(%di) \r
123 jne FindVARSTORE\r
124 cmpl $LOADER_FILENAME_PART3, 7(%di) \r
125 jne FindVARSTORE\r
126 movw 26(%di), %bx # bx = Start Cluster for EFILDR <----------------------------------\r
127 testw %dx, %dx\r
128 je FindNext # Efivar.bin is not loaded\r
129 jmp FoundAll\r
130 \r
131 FindVARSTORE: \r
132 ##if the file is not loader file, see if it's "EFIVAR BIN"\r
133 cmpl $0x56494645, (%di) # Compare to "EFIV"\r
134 jne FindNext\r
135 cmpl $0x20205241, 4(%di) # Compare to "AR "\r
136 jne FindNext\r
137 cmpl $0x4e494220, 7(%di) # Compare to " BIN"\r
138 jne FindNext\r
139 movw %di, %dx # dx = Offset of Start Cluster for Efivar.bin <---------------------\r
140 addw $26, %dx\r
141 testw %bx, %bx\r
142 je FindNext # Efildr is not loaded\r
143 jmp FoundAll\r
144 \r
145 FindNext: \r
146 # go to next find\r
147 addw $FAT_DIRECTORY_ENTRY_SIZE, %di # Increment di\r
148 subw $FAT_DIRECTORY_ENTRY_SIZE, %cx # Decrement cx\r
149 # TODO: jump to FindVarStore if ...\r
150 jne FindEFILDR\r
151 jmp NotFoundAll\r
152 \r
153 FoundAll: \r
154 FoundEFILDR: \r
155 movw %bx, %cx # cx = Start Cluster for EFILDR <----------------------------------\r
156 movw %cs, %ax # Destination = 2000:0000\r
157 addw $0x2000, %ax\r
158 movw %ax, %es\r
159 xorw %di, %di\r
160 ReadFirstClusterOfEFILDR: \r
161 movw %cx, %ax # ax = StartCluster\r
162 subw $2, %ax # ax = StartCluster - 2\r
163 xorb %bh, %bh\r
164 movb SectorsPerCluster(%bp), %bl # bx = SectorsPerCluster\r
165 pushw %dx\r
166 mulw %bx\r
167 popw %dx # ax = (StartCluster - 2) * SectorsPerCluster\r
168 addw (%bp), %ax # ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster\r
169 xorb %bh, %bh\r
170 movb SectorsPerCluster(%bp), %bl # bx = Number of Sectors in a cluster\r
171 pushw %es\r
172 call ReadBlocks\r
173 popw %ax\r
174 JumpIntoFirstSectorOfEFILDR: \r
175 movw %ax, JumpSegment(%bp)\r
176 JumpFarInstruction: \r
177 .byte 0xea\r
178 JumpOffset: \r
179 .word 0x000\r
180 JumpSegment: \r
181 .word 0x2000\r
182 \r
183 \r
184 PrintString: \r
185 movw $0xb800, %ax\r
186 movw %ax, %es\r
187 movw $0x7c0, %ax\r
188 movw %ax, %ds\r
189 movw $7, %cx\r
190 movw $160, %di\r
191 rep\r
192 movsw\r
193 ret\r
194 # ****************************************************************************\r
195 # ReadBlocks - Reads a set of blocks from a block device\r
196 #\r
197 # AX = Start LBA\r
198 # BX = Number of Blocks to Read\r
199 # ES:DI = Buffer to store sectors read from disk\r
200 # ****************************************************************************\r
201 \r
202 # cx = Blocks\r
203 # bx = NumberOfBlocks\r
204 # si = StartLBA\r
205 \r
206 ReadBlocks: \r
207 pusha\r
208 addl LBAOffsetForBootSector(%bp), %eax # Add LBAOffsetForBootSector to Start LBA\r
209 addl HiddenSectors(%bp), %eax # Add HiddenSectors to Start LBA\r
210 movl %eax, %esi # esi = Start LBA\r
211 movw %bx, %cx # cx = Number of blocks to read\r
212 ReadCylinderLoop: \r
213 movw $0x7bfc, %bp # bp = 0x7bfc\r
214 movl %esi, %eax # eax = Start LBA\r
215 xorl %edx, %edx # edx = 0\r
216 movzwl (%bp), %ebx # bx = MaxSector\r
217 divl %ebx # ax = StartLBA / MaxSector\r
218 incw %dx # dx = (StartLBA % MaxSector) + 1\r
219 subw %dx, %bx # bx = MaxSector - Sector\r
220 incw %bx # bx = MaxSector - Sector + 1\r
221 cmpw %bx, %cx # Compare (Blocks) to (MaxSector - Sector + 1)\r
222 jg LimitTransfer\r
223 movw %cx, %bx # bx = Blocks\r
224 LimitTransfer: \r
225 pushw %cx\r
226 movb %dl, %cl # cl = (StartLBA % MaxSector) + 1 = Sector\r
227 xorw %dx, %dx # dx = 0\r
228 divw 2(%bp) # ax = ax / (MaxHead + 1) = Cylinder \r
229 # dx = ax % (MaxHead + 1) = Head\r
230 \r
231 pushw %bx # Save number of blocks to transfer\r
232 movb %dl, %dh # dh = Head\r
233 movw $0x7c00, %bp # bp = 0x7c00\r
234 movb PhysicalDrive(%bp), %dl # dl = Drive Number\r
235 movb %al, %ch # ch = Cylinder\r
236 movb %bl, %al # al = Blocks\r
237 movb $2, %ah # ah = Function 2\r
238 movw %di, %bx # es:bx = Buffer address\r
239 int $0x13\r
240 jc DiskError\r
241 popw %bx\r
242 popw %cx\r
243 movzwl %bx, %ebx\r
244 addl %ebx, %esi # StartLBA = StartLBA + NumberOfBlocks\r
245 subw %bx, %cx # Blocks = Blocks - NumberOfBlocks\r
246 movw %es, %ax\r
247 shlw $(BLOCK_SHIFT-4),%bx\r
248 addw %bx, %ax\r
249 movw %ax, %es # es:di = es:di + NumberOfBlocks*BLOCK_SIZE\r
250 cmpw $0, %cx\r
251 jne ReadCylinderLoop\r
252 popa\r
253 ret\r
254 \r
255 # ****************************************************************************\r
256 # ERROR Condition:\r
257 # ****************************************************************************\r
258 NotFoundAll: \r
259 ## if we found EFILDR, continue\r
260 testw %bx, %bx\r
261 jne FoundEFILDR\r
262 BadBootSector: \r
263 DiskError: \r
264 movw $ErrorString, %si\r
265 call PrintString\r
266 Halt: \r
267 jmp Halt\r
268 \r
269 StartString: \r
270 .byte 'B', 0x0c, 'S', 0x0c, 't', 0x0c, 'a', 0x0c, 'r', 0x0c, 't', 0x0c, '!', 0x0c\r
271 ErrorString: \r
272 .byte 'B', 0x0c, 'E', 0x0c, 'r', 0x0c, 'r', 0x0c, 'o', 0x0c, 'r', 0x0c, '!', 0x0c\r
273 \r
274 # ****************************************************************************\r
275 # LBA Offset for BootSector, need patched by tool for HD boot.\r
276 # ****************************************************************************\r
277 \r
278 .org 0x01fa\r
279 LBAOffsetForBootSector: \r
280 .long 0x0\r
281 \r
282 # ****************************************************************************\r
283 # Sector Signature\r
284 # ****************************************************************************\r
285 \r
286 .org 0x01fe\r
287 SectorSignature: \r
288 .word 0xaa55 # Boot Sector Signature\r
289 \r
290 \r
291 \r