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

; 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
;--------------------------------------------------------------------
%ifndef EXCLUDE_FROM_XTIDECFG
ALIGN JUMP_ALIGN
Drive_GetNumberOfAvailableDrivesToAX:
    push    dx
    push    cx

    call    Drive_GetFlagsForAvailableDrivesToDXAX
    call    Bit_GetSetCountToCXfromDXAX
    xchg    ax, cx

    pop     cx
    pop     dx
    ret
%endif


;--------------------------------------------------------------------
; 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
    cmp     al, 32          ; Number of potentially valid drive letters available
    jb      SHORT .Below32
    mov     al, 32
.Below32:
    cbw
    xchg    cx, ax
    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    ax
    cmp     dl, 1
    jbe     SHORT .FloppyDrive

.MessageSuppressedByInt2FhHandler:
.MoreThanOneFloppyDrive:
.NoFloppyDrive:
    push    bx

    inc     dx          ; Default drive is 00h and first drive is 01h
    mov     ax, CHECK_IF_BLOCK_DEVICE_REMOTE    ; Needs DOS 3.1+
    mov     bx, dx
    push    dx
    int     DOS_INTERRUPT_21h
    pop     dx
    jnc     SHORT .DriveIsValid
    cmp     ax, ERR_DOS_INVALID_DRIVE
    je      SHORT .DriveIsNotValid
    ; Fall back to old method if ERR_DOS_FUNCTION_NUMBER_INVALID

    mov     ah, GET_DOS_DRIVE_PARAMETER_BLOCK_FOR_SPECIFIC_DRIVE
    int     DOS_INTERRUPT_21h
.DriveIsValid:
.DriveIsNotValid:
    dec     dx
    test    al, al

    pop     bx
.ReturnFromFloppyDriveFiltering:
    pop     ax
    pop     ds
    ret

.FloppyDrive:
; On single-floppy-drive systems, both A: and B: will point to the same physical drive. The problem is that DOS will print a message telling the user
; to "insert a disk and press any key to continue" when swapping from one logical drive to the other. To avoid this mess we hook interrupt 2Fh/AX=4A00h
; to signal to DOS that we will handle this ourselves. However, this only works on DOS 5+ so on older DOS versions we instead try to filter out
; the "other" logical drive (the one that isn't the current drive) during drive enumeration so the user can't select the "phantom" drive to begin with.
; This will have the somewhat strange effect of having a drive B: but no drive A: if B: happens to be the current logical floppy drive.

    cmp     BYTE [bDosVersionMajor], 5      ; bDosVersionMajor must be provided by the application as it's not part of the library
    jae     SHORT .MessageSuppressedByInt2FhHandler
    LOAD_BDA_SEGMENT_TO ds, ax
    mov     al, [BDA.wEquipment]
    test    al, 0C0h
    jnz     SHORT .MoreThanOneFloppyDrive   ; No phantom drive so no need for any filtering
    test    al, 1                           ; Any floppy drive at all?
    jz      SHORT .NoFloppyDrive            ; A pre-DOS 5 machine with no FDD is indeed a strange beast. However, don't trust the BIOS - let DOS decide
    cmp     dl, [504h]                      ; MS-DOS - LOGICAL DRIVE FOR SINGLE-FLOPPY SYSTEM (A: / B:)
    jmp     SHORT .ReturnFromFloppyDriveFiltering

;--------------------------------------------------------------------
; .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