| 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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