1 | ; Project name : XTIDE Universal BIOS |
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2 | ; Description : Int 19h Handler (Boot Loader). |
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3 | |
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4 | ; Section containing code |
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5 | SECTION .text |
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6 | |
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7 | ;-------------------------------------------------------------------- |
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8 | ; Int19h_BootLoaderHandler |
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9 | ; Parameters: |
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10 | ; Nothing |
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11 | ; Returns: |
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12 | ; Never returns (loads operating system) |
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13 | ;-------------------------------------------------------------------- |
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14 | ALIGN JUMP_ALIGN |
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15 | Int19h_BootLoaderHandler: |
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16 | LOAD_BDA_SEGMENT_TO es, ax |
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17 | call Initialize_AndDetectDrives ; Installs new boot menu loader |
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18 | ; Fall to .PrepareStackAndSelectDriveFromBootMenu |
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19 | |
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20 | ;-------------------------------------------------------------------- |
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21 | ; .PrepareStackAndSelectDriveFromBootMenu |
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22 | ; Parameters: |
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23 | ; ES: BDA and interrupt vector segment (zero) |
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24 | ; Returns: |
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25 | ; Never returns (loads operating system) |
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26 | ;-------------------------------------------------------------------- |
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27 | .PrepareStackAndSelectDriveFromBootMenu: |
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28 | STORE_POST_STACK_POINTER |
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29 | SWITCH_TO_BOOT_MENU_STACK |
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30 | ; Fall to .InitializeDisplay |
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31 | |
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32 | ;-------------------------------------------------------------------- |
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33 | ; .InitializeDisplay |
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34 | ; Parameters: |
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35 | ; Nothing |
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36 | ; Returns: |
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37 | ; Never returns (loads operating system) |
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38 | ;-------------------------------------------------------------------- |
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39 | .InitializeDisplay: |
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40 | ; Change display mode if necessary |
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41 | mov ax, [cs:ROMVARS.wDisplayMode] ; AH 00h = Set Video Mode |
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42 | cmp al, DEFAULT_TEXT_MODE |
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43 | je SHORT .InitializeDisplayLibrary |
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44 | int BIOS_VIDEO_INTERRUPT_10h |
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45 | .InitializeDisplayLibrary: |
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46 | call BootMenuPrint_InitializeDisplayContext |
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47 | ; Fall to .SelectDriveToBootFrom |
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48 | |
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49 | ;-------------------------------------------------------------------- |
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50 | ; .SelectDriveToBootFrom |
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51 | ; Parameters: |
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52 | ; Nothing |
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53 | ; Returns: |
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54 | ; Never returns (loads operating system) |
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55 | ;-------------------------------------------------------------------- |
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56 | .SelectDriveToBootFrom: |
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57 | call RamVars_GetSegmentToDS |
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58 | cmp WORD [cs:ROMVARS.wfDisplayBootMenu], BYTE 0 |
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59 | jne SHORT ProcessBootMenuSelectionsUntilBootableDriveSelected ; Display boot menu |
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60 | ; Fall to BootFromDriveAthenTryDriveC |
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61 | |
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62 | ;-------------------------------------------------------------------- |
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63 | ; BootFromDriveAthenTryDriveC |
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64 | ; Parameters: |
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65 | ; DS: RAMVARS segment |
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66 | ; Returns: |
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67 | ; Never returns (loads operating system) |
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68 | ;-------------------------------------------------------------------- |
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69 | BootFromDriveAthenTryDriveC: |
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70 | xor dx, dx ; DL = 00h = Floppy Drive A |
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71 | call BootSector_TryToLoadFromDriveDL |
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72 | jc SHORT Int19hMenu_JumpToBootSector_or_RomBoot |
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73 | mov dl, 80h ; DL = 80h = First Hard Drive (usually C) |
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74 | call BootSector_TryToLoadFromDriveDL |
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75 | jmp SHORT Int19hMenu_JumpToBootSector_or_RomBoot ; ROM Boot if error |
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76 | |
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77 | |
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78 | ;-------------------------------------------------------------------- |
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79 | ; ProcessBootMenuSelectionsUntilBootableDriveSelected |
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80 | ; Parameters: |
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81 | ; DS: RAMVARS segment |
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82 | ; Returns: |
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83 | ; Never returns |
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84 | ;-------------------------------------------------------------------- |
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85 | ProcessBootMenuSelectionsUntilBootableDriveSelected: |
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86 | call BootMenu_DisplayAndReturnSelectionInDX |
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87 | call DriveXlate_ToOrBack ; Translate drive number |
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88 | call BootSector_TryToLoadFromDriveDL |
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89 | jnc SHORT ProcessBootMenuSelectionsUntilBootableDriveSelected ; Boot failure, show menu again |
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90 | ; Fall to Int19hMenu_JumpToBootSector_or_RomBoot |
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91 | ; (CF is set or we wouldn't be here, see "jnc" immediately above) |
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92 | |
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93 | ;-------------------------------------------------------------------- |
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94 | ; Int19hMenu_JumpToBootSector_or_RomBoot |
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95 | ; |
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96 | ; Switches back to the POST stack, clears the DS and ES registers, |
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97 | ; and either jumps to the MBR (Master Boot Record) that was just read, |
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98 | ; or calls the ROM's boot routine on interrupt 18. |
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99 | ; |
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100 | ; Parameters: |
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101 | ; DL: Drive to boot from (translated, 00h or 80h) |
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102 | ; CF: Set for Boot Sector Boot |
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103 | ; Clear for Rom Boot |
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104 | ; ES:BX: (if CF set) Ptr to boot sector |
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105 | ; |
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106 | ; Returns: |
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107 | ; Never returns |
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108 | ;-------------------------------------------------------------------- |
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109 | ALIGN JUMP_ALIGN |
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110 | Int19hMenu_JumpToBootSector_or_RomBoot: |
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111 | mov cx, es ; Preserve MBR segment (can't push because of stack change) |
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112 | mov ax, 0 ; NOTE: can't use XOR (LOAD_BDA_SEGMENT_TO) as it impacts CF |
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113 | SWITCH_BACK_TO_POST_STACK |
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114 | |
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115 | ; clear segment registers before boot sector or rom call |
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116 | mov ds, ax |
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117 | mov es, ax |
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118 | %ifdef USE_386 |
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119 | mov fs, ax |
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120 | mov gs, ax |
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121 | %endif |
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122 | jnc SHORT .romboot |
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123 | |
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124 | ; jump to boot sector |
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125 | push cx ; sgment address for MBR |
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126 | push bx ; offset address for MBR |
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127 | retf ; NOTE: DL is set to the drive number |
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128 | |
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129 | ; Boot by calling INT 18h (ROM Basic of ROM DOS) |
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130 | .romboot: |
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131 | int BIOS_BOOT_FAILURE_INTERRUPT_18h ; Never returns |
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