source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Initialization/DriveXlate.asm@ 146

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

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Translates drive number when entering INT 13h.
;
; DriveXlate_WhenEnteringInt13h
;   Parameters:
;       DL:     Drive number to be possibly translated
;       DS:     RAMVARS segment
;   Returns:
;       DL:     Translated drive number
;   Corrupts registers:
;       DI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_WhenEnteringInt13h:
    inc     BYTE [RAMVARS.xlateVars+XLATEVARS.bRecurCnt]
    cmp     BYTE [RAMVARS.xlateVars+XLATEVARS.bRecurCnt], 1
    je      SHORT DriveXlate_ToOrBack
    ret


;--------------------------------------------------------------------
; DriveXlate_WhenLeavingInt13hWithReturnValueInDL
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       Nothing
;   Corrupts registers:
;       DI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_WhenLeavingInt13hWithReturnValueInDL:
    dec     BYTE [RAMVARS.xlateVars+XLATEVARS.bRecurCnt]
    ret

;--------------------------------------------------------------------
; Translates drive number when leaving INT 13h.
;
; DriveXlate_WhenLeavingInt13h
;   Parameters:
;       DL:     Drive number to be possibly translated
;       DS:     RAMVARS segment
;   Returns:
;       DL:     Translated drive number
;   Corrupts registers:
;       DI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_WhenLeavingInt13h:
    dec     BYTE [RAMVARS.xlateVars+XLATEVARS.bRecurCnt]
    jz      SHORT DriveXlate_ToOrBack
    ret


;--------------------------------------------------------------------
; Translates drive number to or back.
;
; 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
    call    DriveXlate_SwapFloppyDriveOrHardDisk
    xchg    ax, di
.Return:
    ret


;--------------------------------------------------------------------
; Swaps Floppy Drive or Hard Disk number.
;
; DriveXlate_SwapFloppyDriveOrHardDisk
;   Parameters:
;       DL:     Drive number to be possibly swapped
;       DS:     RAMVARS segment
;   Returns:
;       DL:     Translated drive number
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_SwapFloppyDriveOrHardDisk:
    mov     ah, 80h                 ; Assume hard disk
    mov     al, BYTE [RAMVARS.xlateVars+XLATEVARS.bHDSwap]
    test    dl, ah                  ; Hard disk?
    jnz     SHORT SwapDrive         ; If so, jump to swap
    mov     al, BYTE [RAMVARS.xlateVars+XLATEVARS.bFDSwap]
    cbw
    ; Fall to SwapDrive

;--------------------------------------------------------------------
; SwapDrive
;   Parameters:
;       AL:     Drive number to swap to 00h/80h
;       AH:     00h/80h to be swapped to stored drive number
;       DL:     Drive number to be possibly swapped
;   Returns:
;       DL:     Translated drive number
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
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?
    je      SHORT .SwapTo00hOr80hInAH
    ret
ALIGN JUMP_ALIGN
.SwapTo00hOr80hInAH:
    mov     dl, ah
    ret
ALIGN JUMP_ALIGN
.SwapToXXhInAL:
    mov     dl, al
    ret


;--------------------------------------------------------------------
; Resets drive swapping variables to defaults (no swapping).
;
; DriveXlate_Reset
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_Reset:
    mov     WORD [RAMVARS.xlateVars], 8000h ; .bFDSwap and .bHDSwap
    mov     BYTE [RAMVARS.xlateVars+XLATEVARS.bRecurCnt], 0
    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


;--------------------------------------------------------------------
; Checks if INT 13h function returns some value in DL
; (other than the drive number that was also parameter).
;
; DriveXlate_DoesFunctionReturnSomethingInDL
;   Parameters:
;       AH:     INT 13h BIOS Function
;       DL:     Drive number
;   Returns:
;       CF:     Set if something is returned in DL
;               Cleared if only drive number parameter is returned in DL
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DriveXlate_DoesFunctionReturnSomethingInDL:
    cmp     ah, 08h         ; AH=08h, Read Disk Drive Parameters?
    je      SHORT DriveXlate_FunctionReturnsSomethingInDL
    test    dl, dl
    jns     SHORT DriveXlate_DoesFloppyFunctionReturnSomethingInDL
    ; Fall to DriveXlate_DoesHardDiskFunctionReturnSomethingInDL

;--------------------------------------------------------------------
; Checks if INT 13h hard disk or floppy drive function returns some
; value in DL other than the drive number that was also parameter).
; Some functions return different values for hard disks and floppy drives.
;
; DriveXlate_DoesHardDiskFunctionReturnSomethingInDL
; DriveXlate_DoesFloppyFunctionReturnSomethingInDL
;   Parameters:
;       AH:     INT 13h BIOS Function
;       DL:     Hard Disk number
;   Returns:
;       CF:     Set if something is returned in DL
;               Cleared if only drive number parameter is returned in DL
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
; ALIGN JUMP_ALIGN
DriveXlate_DoesHardDiskFunctionReturnSomethingInDL:
    cmp     ah, 15h         ; AH=15h, Read Disk Drive Size?
    je      SHORT DriveXlate_FunctionReturnsSomethingInDL
DriveXlate_DoesFloppyFunctionReturnSomethingInDL:
    clc
    ret

ALIGN JUMP_ALIGN
DriveXlate_FunctionReturnsSomethingInDL:
    stc
    ret