source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Initialization/DriveXlate.asm@ 385

; Project name  :   XTIDE Universal BIOS
; Description   :   Functions for swapping drive letters.

;
; 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

;--------------------------------------------------------------------
; DriveXlate_ToOrBack
;   Parameters:
;       DL:     Drive number to be possibly translated
;       DS:     RAMVARS segment
;   Returns:
;       DL:     Translated drive number
;   Corrupts registers:
;       DI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_ToOrBack:
    test    BYTE [cs:ROMVARS.wFlags], FLG_ROMVARS_DRVXLAT
    jz      SHORT .Return           ; Return if translation disabled
    xchg    di, ax                  ; Backup AX

    mov     ah, 80h                 ; Assume hard disk
    mov     al, [RAMVARS.xlateVars+XLATEVARS.bHDSwap]
    test    dl, ah                  ; Hard disk?
    jnz     SHORT .SwapDrive        ; If so, jump to swap
    mov     al, [RAMVARS.xlateVars+XLATEVARS.bFDSwap]
    cbw

ALIGN JUMP_ALIGN
.SwapDrive:
    cmp     ah, dl                  ; Swap DL from 00h/80h to xxh?
    je      SHORT .SwapToXXhInAL
    cmp     al, dl                  ; Swap DL from xxh to 00h/80h?
    jne     SHORT .RestoreAXandReturn
    mov     al, ah
ALIGN JUMP_ALIGN
.SwapToXXhInAL:
    mov     dl, al
ALIGN JUMP_ALIGN
.RestoreAXandReturn:
    xchg    ax, di                  ; Restore AX
ALIGN JUMP_ALIGN, ret
.Return:
    ret


;--------------------------------------------------------------------
; Resets drive swapping variables to defaults (no swapping).
;
; DriveXlate_Reset
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       Nothing
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_Reset:
    mov     WORD [RAMVARS.xlateVars+XLATEVARS.wFDandHDswap], 8000h
    ret


;--------------------------------------------------------------------
; Stores drive to be swapped.
;
; DriveXlate_SetDriveToSwap
;   Parameters:
;       DL:     Drive to swap to 00h or 80h
;       DS:     RAMVARS segment
;   Returns:
;       Nothing
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_SetDriveToSwap:
    test    dl, dl              ; Floppy drive?
    js      SHORT .SetHardDiskToSwap
.SetFloppyDriveToSwap:
    mov     [RAMVARS.xlateVars+XLATEVARS.bFDSwap], dl
    ret
ALIGN JUMP_ALIGN
.SetHardDiskToSwap:
    mov     [RAMVARS.xlateVars+XLATEVARS.bHDSwap], dl
    ret