source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Handlers/Int19h.asm@ 536

; Project name  :   XTIDE Universal BIOS
; Description   :   Int 19h Handler (Boot Loader).

;
; XTIDE Universal BIOS and Associated Tools
; Copyright (C) 2009-2010 by Tomi Tilli, 2011-2013 by XTIDE Universal BIOS Team.
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 2 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; GNU General Public License for more details.
; Visit http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
;

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Int19h_BootLoaderHandler
;   Parameters:
;       Nothing
;   Returns:
;       Never returns (loads operating system)
;--------------------------------------------------------------------
Int19h_BootLoaderHandler:
    sti                                 ; Enable interrupts
    cld                                 ; String instructions to increment pointers
    LOAD_BDA_SEGMENT_TO es, ax          ; Load BDA segment (zero) to ES
    ; Fall to .PrepareBootLoaderStack


;--------------------------------------------------------------------
; Drive detection and boot menu use lots of stack so it is
; wise to relocate stack. Otherwise something important from
; interrupt vectors are likely corrupted, likely our own DPTs if
; they are located to 30:0h.
;
; .PrepareBootLoaderStack
;   Parameters:
;       ES:     BDA and interrupt vector segment (zero)
;   Returns:
;       Never returns (loads operating system)
;--------------------------------------------------------------------
.PrepareBootLoaderStack:
    STORE_POST_STACK_POINTER
    SWITCH_TO_BOOT_MENU_STACK
    ; Fall to .InitializeDisplay


;--------------------------------------------------------------------
; .InitializeDisplay
;   Parameters:
;       ES:     BDA and interrupt vector segment (zero)
;   Returns:
;       Never returns (loads operating system)
;--------------------------------------------------------------------
.InitializeDisplay:
    ; Change display mode if necessary
    mov     ax, [cs:ROMVARS.wDisplayMode]   ; AH 00h = Set Video Mode
    cmp     al, DEFAULT_TEXT_MODE
    je      SHORT .InitializeDisplayLibrary
    int     BIOS_VIDEO_INTERRUPT_10h
.InitializeDisplayLibrary:
    call    DetectPrint_InitializeDisplayContext
    ; Fall to .InitializeBiosAndDetectDrives


;--------------------------------------------------------------------
; .InitializeBiosAndDetectDrives
;   Parameters:
;       ES:     BDA and interrupt vector segment (zero)
;   Returns:
;       DS:     RAMVARS segment
;--------------------------------------------------------------------
%ifdef MODULE_HOTKEYS
    call    TimerTicks_ReadFromBdaToAX
    mov     [es:BOOTVARS.hotkeyVars+HOTKEYVARS.wTimeWhenDisplayed], ax
%endif

    call    Initialize_AndDetectDrives

%ifdef MODULE_HOTKEYS
.WaitUntilTimeToCloseHotkeyBar:
    call    TimerTicks_ReadFromBdaToAX
    sub     ax, [es:BOOTVARS.hotkeyVars+HOTKEYVARS.wTimeWhenDisplayed]
    cmp     ax, MIN_TIME_TO_DISPLAY_HOTKEY_BAR
    jb      SHORT .WaitUntilTimeToCloseHotkeyBar
%endif
    ; Fall to SelectDriveToBootFrom


;--------------------------------------------------------------------
; SelectDriveToBootFrom
;   Parameters:
;       DS:     RAMVARS segment
;       ES:     BDA and interrupt vector segment (zero)
;   Returns:
;       Never returns (loads operating system)
;--------------------------------------------------------------------
; The following macro could be easily inlined below.  Why a macro?  Depending on the combination
; of MODULE_HOTKEYS or MODULE_BOOT_MENU, this code needs to either come before or after the
; call to the boot menu.
;
%macro TRY_TO_BOOT_DL_AND_DH_DRIVES 0
    push    dx                                  ; it's OK if this is left on the stack, if we are
                                                ; successful, the following call does not return
    call    BootSector_TryToLoadFromDriveDL_AndBoot
    pop     dx
    mov     dl, dh
    call    BootSector_TryToLoadFromDriveDL_AndBoot
%endmacro


SelectDriveToBootFrom:      ; Function starts here
%ifdef MODULE_HOTKEYS
    call    HotkeyBar_UpdateDuringDriveDetection
    mov     al, [es:BOOTVARS.hotkeyVars+HOTKEYVARS.bScancode]
    cmp     al, ROM_BOOT_HOTKEY_SCANCODE
    je      SHORT .RomBoot                      ; CF clear so ROM boot
%ifdef MODULE_BOOT_MENU
    cmp     al, BOOT_MENU_HOTKEY_SCANCODE
    je      SHORT .BootMenu
%endif ; MODULE_BOOT_MENU

.TryUsingHotKeysCode:
    call    HotkeyBar_GetBootDriveNumbersToDX
    call    DriveXlate_SetDriveToSwap           ; Enable primary boot device translation
    xchg    dl, dh
    call    DriveXlate_SetDriveToSwap           ; Enable secondary boot device translation
    xchg    dl, dh
    call    DriveXlate_ToOrBack                 ; Translate now so boot device will appear as 00h or 80h to OS
    TRY_TO_BOOT_DL_AND_DH_DRIVES
    ;; falls through to boot menu, if it is present.  If not present, falls through to rom boot.
%endif ; MODULE_HOTKEYS


%ifdef MODULE_BOOT_MENU
.BootMenu:
    call    BootMenu_DisplayAndReturnDriveInDLRomBootClearCF
    jnc     SHORT .RomBoot                      ; CF clear so ROM boot

    call    DriveXlate_Reset
%ifdef MODULE_HOTKEYS
    jmp     SHORT .TryUsingHotKeysCode          ; Selected drive stored as hotkey
%else ; Boot menu without hotkeys, secondary boot drive is always 00h or 80h
    mov     dh, dl                              ; Setup for secondary drive
    not     dh                                  ; Floppy goes to HD, or vice versa
    and     dh, 80h                             ; Go to first drive of the floppy or HD set
    call    DriveXlate_SetDriveToSwap
    call    DriveXlate_ToOrBack
    TRY_TO_BOOT_DL_AND_DH_DRIVES
    jmp     SHORT .BootMenu                     ; Show boot menu again
%endif ; MODULE_HOTKEYS

%endif ; MODULE_BOOT_MENU

; No hotkeys and no boot menu means fixed "A then C" boot order
%ifndef MODULE_HOTKEYS OR MODULE_BOOT_MENU
    xor     dl, dl                              ; Try to boot from Floppy Drive A
    call    BootSector_TryToLoadFromDriveDL_AndBoot
    mov     dl, 80h                             ; Try to boot from Hard Drive C
    call    BootSector_TryToLoadFromDriveDL_AndBoot
%endif

.RomBoot:
%ifdef MODULE_DRIVEXLATE
    call    DriveXlate_Reset                    ; Clean up any drive mappings before Rom Boot
%endif
    clc
    ;; fall through to Int19_JumpToBootSectorOrRomBoot

;--------------------------------------------------------------------
; Int19_JumpToBootSectorOrRomBoot
;
; Switches back to the POST stack, clears the DS and ES registers,
; and either jumps to the MBR (Master Boot Record) that was just read,
; or calls the ROM's boot routine on interrupt 18.
;
;   Parameters:
;       DL:     Drive to boot from (translated, 00h or 80h)
;       CF:     Set for Boot Sector Boot
;               Clear for ROM Boot
;       ES:BX:  (if CF set) Ptr to boot sector
;
;   Returns:
;       Never returns
;--------------------------------------------------------------------
Int19_JumpToBootSectorOrRomBoot:
    mov     cx, es      ; Preserve MBR segment (can't push because of stack change)
    mov     ax, 0       ; NOTE: can't use XOR (LOAD_BDA_SEGMENT_TO) as it impacts CF
    SWITCH_BACK_TO_POST_STACK

; clear segment registers before boot sector or rom call
    mov     ds, ax
    mov     es, ax
%ifdef USE_386
    mov     fs, ax
    mov     gs, ax
%endif
    jnc     SHORT .romboot

; jump to boot sector
    push    cx          ; sgment address for MBR
    push    bx          ; offset address for MBR
    retf                ; NOTE: DL is set to the drive number

; Boot by calling INT 18h (ROM Basic of ROM DOS)
.romboot:
    int     BIOS_BOOT_FAILURE_INTERRUPT_18h ; Never returns