scoutos / prex-0.9.0 / bsp / boot / x86 / tools / bootsect / bootsect.S @ 03e9c04a
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1 | 03e9c04a | Brad Neuman | /*- |
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2 | * Copyright (c) 2005, Kohsuke Ohtani |
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3 | * All rights reserved. |
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4 | * |
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5 | * Redistribution and use in source and binary forms, with or without |
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6 | * modification, are permitted provided that the following conditions |
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7 | * are met: |
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8 | * 1. Redistributions of source code must retain the above copyright |
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9 | * notice, this list of conditions and the following disclaimer. |
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10 | * 2. Redistributions in binary form must reproduce the above copyright |
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11 | * notice, this list of conditions and the following disclaimer in the |
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12 | * documentation and/or other materials provided with the distribution. |
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13 | * 3. Neither the name of the author nor the names of any co-contributors |
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14 | * may be used to endorse or promote products derived from this software |
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15 | * without specific prior written permission. |
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16 | * |
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17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND |
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18 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
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19 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
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20 | * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE |
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21 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
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22 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
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23 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
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24 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
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25 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
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26 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
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27 | * SUCH DAMAGE. |
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28 | */ |
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29 | |||
30 | /** |
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31 | * bootsect.S - Boot sector for FAT |
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32 | * |
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33 | * The boot sector is 512 byte code to load the OS image. It is loaded |
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34 | * to address 0:7c00 by POST BIOS. |
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35 | * The boot sector searches the target file within the root directory of |
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36 | * FAT file system, and loads it to predefined memory address. Then, it |
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37 | * jumps to the first byte of the loaded image. |
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38 | * |
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39 | * All disk access are done by using BIOS Int13h interface. The BIOS |
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40 | * parameter block (BPB) has the disk/FAT information, and it exists |
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41 | * in the first portion of the FAT boot sector. It must be filled by the |
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42 | * FAT format utility, or the prex kernel install utility (mkboot.com). |
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43 | * This program assumes that correct BPB is stored in the boot sector. |
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44 | * |
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45 | * Limitation: |
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46 | * - Support only FAT12/16. FAT32 is not supported. |
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47 | * |
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48 | * Memory usage: |
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49 | * > 5000 - 6FFF ... Disk work area |
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50 | * > 7000 - 7BFF ... Stack |
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51 | * > 7C00 - 7DFF ... This boot sector |
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52 | * >10000 - ... FAT cache |
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53 | * >20000 - ... Data cache |
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54 | * >30000 - ... Image load address |
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55 | */ |
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56 | .code16 |
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57 | .text |
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58 | .align 1 |
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59 | |||
60 | # Memory locations |
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61 | #define BOOT_STACK 0x7c00 |
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62 | |||
63 | #define LOAD_ADDR 0x30000 |
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64 | #define ENTRY_SEG 0x3000 |
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65 | #define ENTRY_OFF 0x0000 |
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66 | |||
67 | #define WORK_AREA 0x5000 |
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68 | #define FAT_SEG 0x1000 |
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69 | #define DATA_SEG 0x2000 |
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70 | |||
71 | #define LOAD_MAX 0xA0000 |
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72 | |||
73 | # FAT Directory entry |
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74 | #define F_NAME 0 |
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75 | #define F_ATTR 11 |
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76 | #define F_RESERVED 12 |
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77 | #define F_TIME 22 |
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78 | #define F_DATA 24 |
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79 | #define F_CLUSTER 26 |
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80 | #define F_SIZE 28 |
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81 | |||
82 | #define DIR_SIZE 32 |
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83 | #define DIRENT_PER_SECTOR 16 |
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84 | |||
85 | # BIOS parameter block (BPB) location (%bp points to 0x7c00) |
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86 | #define OEM_ID 0x03(%bp) |
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87 | #define BYTE_PER_SECTOR 0x0b(%bp) |
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88 | #define SECT_PER_CLUSTER 0x0d(%bp) |
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89 | #define RESERVED_SECTORS 0x0e(%bp) |
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90 | #define NUM_OF_FATS 0x10(%bp) |
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91 | #define ROOT_ENTRIES 0x11(%bp) |
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92 | #define TOTAL_SECTORS 0x13(%bp) |
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93 | #define MEDIA_DESCRIPTOR 0x15(%bp) |
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94 | #define SECTORS_PER_FAT 0x16(%bp) |
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95 | #define SECTORS_PER_TRACK 0x18(%bp) |
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96 | #define HEADS 0x1a(%bp) |
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97 | #define HIDDEN_SECTORS 0x1c(%bp) |
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98 | #define BIG_TOTAL_SECTORS 0x20(%bp) |
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99 | #define PHYSICAL_DRIVE 0x24(%bp) |
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100 | #define EXT_BOOT_SIGNATURE 0x26(%bp) |
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101 | #define SERIAL_NO 0x27(%bp) |
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102 | #define VOLUME_ID 0x2b(%bp) |
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103 | #define FILE_SYS_ID 0x36(%bp) |
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104 | |||
105 | #define FILE_SYS_ID_NUM 0x3a(%bp) |
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106 | |||
107 | # Local data area (Note: These data will overlap the existing code) |
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108 | #define FAT_START 0x40(%bp) |
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109 | #define DATA_START 0x44(%bp) |
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110 | |||
111 | .global _boot |
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112 | |||
113 | # |
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114 | # Boot the system |
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115 | # |
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116 | _boot: |
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117 | jmp start # Skip BPB |
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118 | nop # Nop is for DOS compatibility |
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119 | |||
120 | # |
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121 | # BPB |
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122 | # |
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123 | .ascii "PREX1.00" |
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124 | .fill 0x33, 1, 0 # Drive parameter must be |
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125 | # filled by intaller |
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126 | |||
127 | # |
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128 | # Setup stack and segment registers |
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129 | # |
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130 | start: |
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131 | cli |
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132 | cld # Clear direction flag |
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133 | xorl %eax, %eax # Set EAX to zero |
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134 | movw %ax, %ds |
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135 | movw %ax, %es |
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136 | movw %ax, %ss |
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137 | movw $(BOOT_STACK), %sp |
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138 | movw %sp, %bp # EBP = Bios Parameter Block |
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139 | sti |
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140 | |||
141 | # |
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142 | # Display boot message |
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143 | # |
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144 | movw $load_msg, %si |
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145 | movw $21, %cx |
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146 | call puts |
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147 | |||
148 | # |
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149 | # Store disk information |
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150 | # |
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151 | movl HIDDEN_SECTORS, %ebx # Get hidden sector |
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152 | movw RESERVED_SECTORS, %ax # Add reserved sector |
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153 | addl %eax, %ebx # High 16 bit of EAX is 0 |
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154 | movl %ebx, FAT_START # FAT start = hidden + reserved |
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155 | |||
156 | movzbw NUM_OF_FATS, %ax # Normally 2 |
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157 | mulw SECTORS_PER_FAT # AX = Num of sector of FATs |
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158 | addl %ebx, %eax # EAX = Start of root directory |
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159 | |||
160 | movw ROOT_ENTRIES, %bx |
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161 | shrw $4, %bx # / 16 = DIRENT_PER_SECTOR |
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162 | movw %bx, %cx # CX = Num of sectors for root directory |
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163 | |||
164 | addl %eax, %ebx # DATA start = FAT start + root |
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165 | movl %ebx, DATA_START # Start sector of data area |
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166 | |||
167 | # |
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168 | # Find the OS image in the root directory |
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169 | # |
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170 | # EAX = Start sector of root |
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171 | next_sector: |
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172 | pushw %cx |
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173 | movl $(WORK_AREA), %ebx |
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174 | pushw %bx |
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175 | call read_sector # Read 1 sector in root |
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176 | popw %di # DI = dir_entry |
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177 | movw $(DIRENT_PER_SECTOR), %cx # CX = directory count |
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178 | next_entry: |
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179 | cmpb $0, (%di) # End of dir entry ? |
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180 | je error # Not found |
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181 | testb $0x18, F_ATTR(%di) # Subdir or Volume ? |
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182 | jnz not_file # Skip it |
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183 | pusha |
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184 | movw $11, %cx # File name + ext = 11 byte |
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185 | movw $image_name, %si |
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186 | repe # Compare file name |
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187 | cmpsb |
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188 | popa |
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189 | je found_file |
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190 | not_file: |
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191 | addw $(DIR_SIZE), %di # Check next directory entry |
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192 | loop next_entry |
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193 | popw %cx |
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194 | loop next_sector |
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195 | # Fall through |
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196 | # |
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197 | # Error case |
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198 | # |
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199 | error: |
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200 | movw $err_msg, %si |
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201 | movw $5, %cx |
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202 | call puts |
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203 | hang: |
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204 | hlt |
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205 | jmp hang # Stop here |
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206 | |||
207 | # |
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208 | # Load image |
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209 | # |
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210 | found_file: |
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211 | movzwl F_CLUSTER(%di), %eax # EAX = 1st cluster of loader |
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212 | movl $(LOAD_ADDR), %ebx # EBX = 32bit load address |
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213 | load_next: |
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214 | call read_cluster # Read cluster of loader |
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215 | call next_cluster # Get next cluster# in EAX |
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216 | jb load_next # EOF ? |
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217 | |||
218 | # |
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219 | # Turn fdd motor off |
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220 | # |
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221 | movw $0x3f2, %dx |
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222 | xorb %al, %al |
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223 | outb %al, %dx |
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224 | |||
225 | # |
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226 | # Jump to loaded image |
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227 | # |
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228 | ljmp $0x3000, $0x0 |
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229 | |||
230 | # |
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231 | # Puts - Print string |
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232 | # |
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233 | # Entry: |
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234 | # SI - Pointer to message string |
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235 | # CX - Number of character |
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236 | # |
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237 | puts: |
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238 | lodsb |
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239 | movb $0x0e, %ah |
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240 | movw $0x0007, %bx |
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241 | int $0x10 |
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242 | loop puts |
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243 | ret |
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244 | |||
245 | # |
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246 | # next_cluster - Return next cluster |
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247 | # |
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248 | # Entry: |
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249 | # EAX - Current cluter# |
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250 | # |
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251 | # Exit: |
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252 | # AF - End of cluster |
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253 | # EAX - Next cluter# |
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254 | # |
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255 | # Modified: |
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256 | # Flags,CX,EDX,SI,DI |
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257 | # |
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258 | next_cluster: |
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259 | pushl %ebx |
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260 | movw %ax, %di # Save cluster# in DI |
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261 | |||
262 | movw $0xfff8, %si # Set default EOF to FAT16 |
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263 | |||
264 | movl %eax, %ecx |
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265 | shll $1, %eax # * 2 |
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266 | |||
267 | cmpb $0x36, FILE_SYS_ID_NUM # ID is 'FAT16' ? |
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268 | je fat_16 |
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269 | addl %ecx, %eax # * 3 |
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270 | shrl $1, %eax # / 2 |
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271 | movw $0xff8, %si # EOF for FAT12 |
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272 | fat_16: |
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273 | # EAX - Offset of FAT entry |
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274 | xorw %dx, %dx |
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275 | divw BYTE_PER_SECTOR |
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276 | addl FAT_START, %eax # EAX = Sector# for FAT |
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277 | # DX = Offset in sector |
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278 | movl $(WORK_AREA), %ebx |
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279 | pushw %bx |
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280 | call read_sector # Read 2 sector for border |
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281 | call read_sector # data |
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282 | popw %bx |
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283 | addw %dx, %bx |
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284 | movw (%bx), %ax |
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285 | cmpw $0xfff8, %si # FAT16 ? |
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286 | je chk_end |
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287 | |||
288 | shrw $1, %di |
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289 | jc odd_pos |
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290 | andb $0x0f, %ah |
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291 | jmp chk_end |
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292 | odd_pos: |
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293 | shrw $4, %ax |
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294 | chk_end: |
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295 | cmpw %si, %ax |
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296 | popl %ebx |
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297 | ret |
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298 | |||
299 | # |
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300 | # read_cluster - Read one cluster |
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301 | # |
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302 | # Entry: |
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303 | # EBX - 32-bit pointer to buffer |
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304 | # EAX - Cluster number |
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305 | # |
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306 | # Exit: |
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307 | # EBX - Point to next buffer |
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308 | # |
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309 | # Modified: |
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310 | # flags,ECX,ECX,EDX |
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311 | # |
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312 | read_cluster: |
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313 | pushl %eax |
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314 | decw %ax # Translate clust# to sec# |
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315 | decw %ax |
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316 | xorl %ecx, %ecx |
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317 | movb SECT_PER_CLUSTER, %cl |
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318 | mull %ecx |
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319 | addl DATA_START, %eax # EAX = Read sec# |
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320 | # CX = Read sector size |
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321 | read_loop: |
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322 | call read_sector |
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323 | cmpl $(LOAD_MAX), %ebx |
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324 | jae error |
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325 | loop read_loop |
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326 | popl %eax |
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327 | ret |
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328 | |||
329 | # |
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330 | # read_sector - Read one sector |
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331 | # |
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332 | # Entry: |
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333 | # EBX - 32-bit pointer to buffer |
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334 | # EAX - Logical sector# to read |
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335 | # |
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336 | # Exit: |
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337 | # EBX - Pointer to next buffer |
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338 | # EAX - Next sector |
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339 | # |
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340 | # Modified: |
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341 | # Flags |
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342 | # |
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343 | read_sector: |
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344 | pushal |
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345 | pushw %ds |
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346 | pushw %es |
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347 | |||
348 | movl %eax, %esi # ESI = buffer |
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349 | |||
350 | movzwl SECTORS_PER_TRACK, %ecx # Get sec/track |
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351 | xorl %edx, %edx |
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352 | divl %ecx # EAX = track# |
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353 | # DX = sec# |
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354 | movw $(DATA_SEG), %cx # Check in cache |
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355 | leaw last_data, %di |
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356 | cmpl DATA_START, %esi |
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357 | jae data_reqest |
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358 | movw $(FAT_SEG), %cx |
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359 | leaw last_fat, %di |
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360 | data_reqest: |
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361 | # CX = Cached segment |
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362 | pushal # [DI] = Cached track |
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363 | movw %cx, %es |
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364 | xorw %bx, %bx # ES:BX = Cache address |
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365 | cmpl (%di), %eax # Last track ? |
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366 | je hit_cache |
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367 | movl %eax, (%di) # Save current track# |
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368 | call read_track |
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369 | hit_cache: |
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370 | popal |
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371 | |||
372 | pushw %es |
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373 | popw %ds |
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374 | |||
375 | shlw $9, %dx # sec# * 512 |
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376 | movw %dx, %si # DS:SI = Offset in cache |
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377 | |||
378 | movw %bx, %di # [EBX] -> ES:[DI] |
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379 | andw $0xf, %di |
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380 | shrl $4, %ebx |
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381 | movw %bx, %es |
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382 | |||
383 | mov $512, %cx # Copy 1 sector |
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384 | rep |
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385 | movsb |
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386 | |||
387 | popw %es |
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388 | popw %ds |
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389 | popal |
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390 | |||
391 | addl $512, %ebx # Next buffer |
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392 | incl %eax # Next sector |
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393 | ret |
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394 | |||
395 | # |
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396 | # read_track - Read one track |
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397 | # |
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398 | # Entry: |
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399 | # ES:[BX] - Pointer to buffer |
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400 | # EAX - Track number to read |
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401 | # |
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402 | # Exit: |
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403 | # None |
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404 | # |
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405 | # Modified: |
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406 | # Flags,EAX,ECX,EDX |
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407 | # |
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408 | read_track: |
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409 | movzwl HEADS, %ecx # Get num of head |
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410 | xorl %edx, %edx |
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411 | divl %ecx # AX = cyl# |
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412 | # DL = head# |
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413 | |||
414 | movb %al, %ch # CH = cyl# (low 8 bits) |
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415 | andb $3, %ah |
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416 | shlb $6, %ah |
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417 | orb $1, %ah |
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418 | movb %ah, %cl # CL[7:6] = cyl# (high 2 bits) |
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419 | # CL[5:0] = sec# = 1 |
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420 | movb %dl, %dh # DH = Head# |
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421 | movw SECTORS_PER_TRACK, %ax # AL = Num of sectors to read |
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422 | movb $2, %ah # AH = 02h (Read Disk Sectors) |
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423 | movb PHYSICAL_DRIVE, %dl # DL = Drive# |
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424 | int $0x13 # Invoke Disk BIOS |
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425 | jc error |
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426 | ret |
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427 | |||
428 | # |
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429 | # Local Data |
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430 | # |
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431 | last_fat: .long 0xffffffff |
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432 | last_data: .long 0xffffffff |
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433 | |||
434 | load_msg: .ascii "Loading " |
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435 | image_name: .ascii "PREXOS " |
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436 | crlf: .byte 0x0a, 0x0d |
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437 | err_msg: .ascii "Error" |
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438 | |||
439 | .org 510 |
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440 | .word 0xaa55 |