source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Menus/BootMenu/BootMenu.asm@ 543

; Project name  :   XTIDE Universal BIOS
; Description   :   Displays Boot Menu.

;
; 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

;--------------------------------------------------------------------
; Displays Boot Menu and returns Drive or Function number.
;
; BootMenu_DisplayAndReturnDriveInDLRomBootClearCF
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       DL:     Drive number selected
;       CF:     Set if selected item is an actual drive, DL is valid
;               Clear if selected item is Rom Boot, DL is invalid
;   Corrupts registers:
;       All General Purpose Registers
;--------------------------------------------------------------------
BootMenu_DisplayAndReturnDriveInDLRomBootClearCF:
    call    DriveXlate_Reset

    mov     bx, BootMenuEvent_Handler
    CALL_MENU_LIBRARY   DisplayWithHandlerInBXandUserDataInDXAX

    xchg    cx, ax

    ; Clear Boot Menu from screen
    mov     ax, ' ' | (MONO_NORMAL<<8)
    CALL_DISPLAY_LIBRARY    ClearScreenWithCharInALandAttrInAH

    ; fall through to BootMenu_GetDriveToDXforMenuitemInCX

;--------------------------------------------------------------------
; BootMenu_GetDriveToDXforMenuitemInCX
;   Parameters:
;       CX:     Index of menuitem selected from Boot Menu
;       DS:     RAMVARS segment
;   Returns:
;       DX:     Drive number to be used for booting
;       CF:     Set: There is a selected menu item, DL is valid
;               Clear: The item selected is Rom Boot, DL is not valid
;   Corrupts registers:
;       AX, BX
;
; NOTE: We can't use the menu structure in here, as we are falling through
; from BootMenu_DisplayAndReturnDriveInDLRomBootClearCF when the
; menu structure has already been destroyed.
;--------------------------------------------------------------------
BootMenu_GetDriveToDXforMenuitemInCX:
    mov     dl, cl                          ; Copy menuitem index to DX
    call    FloppyDrive_GetCountToAX
    cmp     dl, al                          ; Floppy drive?
    jb      SHORT .ReturnFloppyDriveInDX    ; Set CF if branch taken
    or      al, 80h                         ; Or 80h into AL before the sub
                                            ; shorter instruction than or'ing it in afterward
    sub     dl, al                          ; Remove floppy drives from index
    call    RamVars_GetHardDiskCountFromBDAtoAX
    or      al, 80h                         ; Or 80h into AL before the sub
    cmp     dl, al                          ; Set CF if hard disk
                                            ; Clear CF if last item, beyond hard disk list, which indicates ROM boot
.ReturnFloppyDriveInDX:
    ret