source: xtideuniversalbios/trunk/Assembly_Library/Src/File/Drive.asm @ 526

; Project name  :   Assembly Library
; Description   :   Functions for accessing drives.

;
; 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

;--------------------------------------------------------------------
; Drive_GetNumberOfAvailableDrivesToAX
;   Parameters:
;       Nothing
;   Returns:
;       AX:     Number of available drives
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Drive_GetNumberOfAvailableDrivesToAX:
    push    dx
    push    cx

    call    Drive_GetFlagsForAvailableDrivesToDXAX
    call    Bit_GetSetCountToCXfromDXAX
    xchg    ax, cx

    pop     cx
    pop     dx
    ret


;--------------------------------------------------------------------
; Drive_GetFlagsForAvailableDrivesToDXAX
;   Parameters:
;       Nothing
;   Returns:
;       DX:AX:  Flags containing valid drives (bit 0 = drive A, bit 1 = drive B ...)
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Drive_GetFlagsForAvailableDrivesToDXAX:
    push    cx
    push    bx
    mov     dx, DosCritical_HandlerToIgnoreAllErrors
    call    DosCritical_InstallNewHandlerFromCSDX

    call    .GetNumberOfPotentiallyValidDriveLettersToCX
    xor     bx, bx
    xor     ax, ax              ; Temporary use BX:AX for flags
    cwd                         ; Start from drive 0
    call    .CheckDriveValidityUntilCXisZero
    mov     dx, bx              ; Flags now in DX:AX

    call    DosCritical_RestoreDosHandler
    pop     bx
    pop     cx
    ret

;--------------------------------------------------------------------
; .GetNumberOfPotentiallyValidDriveLettersToCX
;   Parameters:
;       Nothing
;   Returns:
;       CX:     Number of potentially valid drive letters available
;   Corrupts registers:
;       AX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.GetNumberOfPotentiallyValidDriveLettersToCX:
    call    Drive_GetDefaultToAL
    xchg    dx, ax          ; Default drive to DL
    call    Drive_SetDefaultFromDL
    eMOVZX  cx, al          ; Number of potentially valid drive letters available
    cmp     cl, 32
    jb      SHORT .Return
    mov     cl, 32
ALIGN JUMP_ALIGN, ret
.Return:
    ret

;--------------------------------------------------------------------
; .CheckDriveValidityUntilCXisZero
;   Parameters:
;       CX:     Number of potentially valid drive letters left
;       DL:     Drive number (00h=A:, 01h=B: ...)
;       BX:AX:  Flags for drive numbers
;   Returns:
;       BX:AX:  Flags for valid drive numbers
;   Corrupts registers:
;       CX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.CheckDriveValidityUntilCXisZero:
    call    .IsValidDriveNumberInDL
    jnz     SHORT .PrepareToCheckNextDrive
    call    .SetFlagToBXAXfromDriveInDL
ALIGN JUMP_ALIGN
.PrepareToCheckNextDrive:
    inc     dx
    loop    .CheckDriveValidityUntilCXisZero
    ret

;--------------------------------------------------------------------
; .IsValidDriveNumberInDL
;   Parameters:
;       DL:     Drive number (00h=A:, 01h=B: ...)
;   Returns:
;       ZF:     Set if drive number is valid
;               Cleared if drive number is invalid
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.IsValidDriveNumberInDL:
    push    ds
    push    bx
    push    ax

    inc     dx          ; Default drive is 00h and first drive is 01h
    mov     ah, GET_DOS_DRIVE_PARAMETER_BLOCK_FOR_SPECIFIC_DRIVE
    int     DOS_INTERRUPT_21h
    dec     dx
    test    al, al

    pop     ax
    pop     bx
    pop     ds
    ret

;--------------------------------------------------------------------
; .SetFlagToBXAXfromDriveInDL
;   Parameters:
;       DL:     Drive number (0...31)
;       BX:AX:  Flags containing drive numbers
;   Returns:
;       BX:AX:  Flags with wanted drive bit set
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.SetFlagToBXAXfromDriveInDL:
    push    cx

    mov     cl, dl
    xchg    dx, bx
    call    Bit_SetToDXAXfromIndexInCL
    xchg    bx, dx

    pop     cx
    ret


;--------------------------------------------------------------------
; Drive_GetDefaultToAL
;   Parameters:
;       Nothing
;   Returns:
;       AL:     Current default drive (00h=A:, 01h=B: ...)
;   Corrupts registers:
;       AH
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Drive_GetDefaultToAL:
    mov     ah, GET_CURRENT_DEFAULT_DRIVE
    SKIP2B  f   ; cmp ax, <next instruction>
    ; Fall to Drive_SetDefaultFromDL


;--------------------------------------------------------------------
; Drive_SetDefaultFromDL
;   Parameters:
;       DL:     New default drive (00h=A:, 01h=B: ...)
;   Returns:
;       AL:     Number of potentially valid drive letters available
;   Corrupts registers:
;       AH
;--------------------------------------------------------------------
Drive_SetDefaultFromDL:
    mov     ah, SELECT_DEFAULT_DRIVE
    int     DOS_INTERRUPT_21h
    ret