source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Handlers/Int19h.asm@ 393

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

;
; XTIDE Universal BIOS and Associated Tools 
; Copyright (C) 2009-2010 by Tomi Tilli, 2011-2012 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                                         ; Allow timer interrupts
    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
;--------------------------------------------------------------------
    call    Initialize_AndDetectDrives  
    ; Fall to SelectDriveToBootFrom


;--------------------------------------------------------------------
; SelectDriveToBootFrom
;   Parameters:
;       DS:     RAMVARS segment
;       ES:     BDA and interrupt vector segment (zero)
;   Returns:
;       Never returns (loads operating system)
;--------------------------------------------------------------------
SelectDriveToBootFrom:
    call    HotkeyBar_UpdateDuringDriveDetection

%ifdef MODULE_BOOT_MENU
    mov     di, BOOTVARS.hotkeyVars+HOTKEYVARS.bScancode
    cmp     BYTE [es:di], BOOT_MENU_HOTKEY_SCANCODE
    jne     SHORT .DoNotDisplayBootMenu

    ; Stop blinking the Boot Menu hotkey and display menu
    mov     BYTE [es:di], 0
    call    HotkeyBar_DrawToTopOfScreen
    call    BootMenu_DisplayAndStoreSelectionAsHotkey
.DoNotDisplayBootMenu:
%endif

    ; Check if ROM boot (INT 18h) wanted
    cmp     BYTE [es:BOOTVARS.hotkeyVars+HOTKEYVARS.bScancode], ROM_BOOT_HOTKEY_SCANCODE
    je      SHORT JumpToBootSector_or_RomBoot   ; CF clear so ROM boot

    ; Try to boot from Primary boot drive (00h by default)
    call    HotkeyBar_GetPrimaryBootDriveNumberToDL
    call    TryToBootFromPrimaryOrSecondaryBootDevice
    jc      SHORT JumpToBootSector_or_RomBoot

    ; Try to boot from Secondary boot device (80h by default)
    call    HotkeyBar_GetSecondaryBootDriveNumberToDL
    call    TryToBootFromPrimaryOrSecondaryBootDevice

%ifdef MODULE_BOOT_MENU
    ; Force Boot Menu hotkey to display boot menu
    mov     BYTE [es:BOOTVARS.hotkeyVars+HOTKEYVARS.bScancode], BOOT_MENU_HOTKEY_SCANCODE
    jnc     SHORT SelectDriveToBootFrom
%endif
    ; Fall to JumpToBootSector_or_RomBoot


;--------------------------------------------------------------------
; JumpToBootSector_or_RomBoot
;
; 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
;--------------------------------------------------------------------
JumpToBootSector_or_RomBoot:
    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 


;--------------------------------------------------------------------
; TryToBootFromPrimaryOrSecondaryBootDevice
;   Parameters
;       DL:     Drive selected as boot device
;       DS:     RAMVARS segment
;       ES:     BDA and interrupt vector segment (zero)
;   Returns:
;       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
;   Corrupts registers:
;       AX, CX, DH, SI, DI, (DL if failed to read boot sector)
;--------------------------------------------------------------------
TryToBootFromPrimaryOrSecondaryBootDevice:
    call    DriveXlate_SetDriveToSwap
    call    DriveXlate_ToOrBack
    jmp     BootSector_TryToLoadFromDriveDL