source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/RamVars.asm@ 93

; Project name  :   XTIDE Universal BIOS
; Description   :   Functions for accessings RAMVARS.

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Initializes RAMVARS.
; Drive detection can be started after this function returns.
;
; RamVars_Initialize
;   Parameters:
;       Nothing
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX, CX, DI, DS
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
RamVars_Initialize:
    push    es
    call    .StealMemoryForRAMVARS  ; Get RAMVARS segment to DS even if no stealing
    call    .ClearRamvarsFromDS
    pop     es
    jmp     DriveXlate_Reset

;--------------------------------------------------------------------
; .StealMemoryForRAMVARS
;   Parameters:
;       Nothing
;   Returns:
;       DS:     RAMVARS segment
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.StealMemoryForRAMVARS:
    test    BYTE [cs:ROMVARS.wFlags], FLG_ROMVARS_FULLMODE
    jz      SHORT RamVars_GetSegmentToDS

    LOAD_BDA_SEGMENT_TO ds, ax      ; Zero AX
    mov     al, [cs:ROMVARS.bStealSize]
    sub     [BDA.wBaseMem], ax
    mov     ax, [BDA.wBaseMem]
    eSHL_IM ax, 6                   ; Segment to first stolen kB (*=40h)
    mov     ds, ax
    ret

;--------------------------------------------------------------------
; .ClearRamvarsFromDS
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX, CX, DI, ES
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.ClearRamvarsFromDS:
    call    FindDPT_PointToFirstDPT ; Get RAMVARS/FULLRAMVARS size to DI
    mov     cx, di                  ; Copy byte count to CX
    push    ds
    pop     es
    xor     di, di                  ; ES:DI now points to RAMVARS/FULLRAMVARS
    xor     ax, ax                  ; Store zeroes
    rep stosb
    mov     WORD [FULLRAMVARS.wSign], W_SIGN_FULLRAMVARS
    ret


;--------------------------------------------------------------------
; Returns segment to RAMVARS.
; RAMVARS might be located at the top of interrupt vectors (0030:0000h)
; or at the top of system base RAM.
;
; RamVars_GetSegmentToDS
;   Parameters:
;       Nothing
;   Returns:
;       DS:     RAMVARS segment
;   Corrupts registers:
;       DI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
RamVars_GetSegmentToDS:
    test    BYTE [cs:ROMVARS.wFlags], FLG_ROMVARS_FULLMODE
    jnz     SHORT .GetStolenSegmentToDS
    mov     di, SEGMENT_RAMVARS_TOP_OF_INTERRUPT_VECTORS
    mov     ds, di
    ret

ALIGN JUMP_ALIGN
.GetStolenSegmentToDS:
    LOAD_BDA_SEGMENT_TO ds, di
    mov     di, [BDA.wBaseMem]      ; Load available base memory size in kB
    eSHL_IM di, 6                   ; Segment to first stolen kB (*=40h)
ALIGN JUMP_ALIGN
.LoopStolenKBs:
    mov     ds, di                  ; EBDA segment to DS
    add     di, BYTE 64             ; DI to next stolen kB
    cmp     WORD [FULLRAMVARS.wSign], W_SIGN_FULLRAMVARS
    jne     SHORT .LoopStolenKBs    ; Loop until sign found (always found eventually)
    ret


;--------------------------------------------------------------------
; Checks if INT 13h function is handled by this BIOS.
;
; RamVars_IsFunctionHandledByThisBIOS
;   Parameters:
;       AH:     INT 13h function number
;       DL:     Drive number
;       DS:     RAMVARS segment
;   Returns:
;       CF:     Set if function is handled by this BIOS
;               Cleared if function belongs to some other BIOS
;   Corrupts registers:
;       DI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
RamVars_IsFunctionHandledByThisBIOS:
    test    ah, ah          ; Reset for all floppy and hard disk drives?
    jz      SHORT .FunctionIsHandledByOurBIOS
    cmp     ah, 08h         ; Read Disk Drive Parameters?
    jne     SHORT RamVars_IsDriveHandledByThisBIOS
    test    dl, 80h         ; We dot not handle floppy drives
    jz      SHORT .FunctionIsNotHandledByOurBIOS
ALIGN JUMP_ALIGN
.FunctionIsHandledByOurBIOS:
    stc
.FunctionIsNotHandledByOurBIOS:
    ret

;--------------------------------------------------------------------
; Checks if drive is handled by this BIOS.
;
; RamVars_IsDriveHandledByThisBIOS
;   Parameters:
;       DL:     Drive number
;       DS:     RAMVARS segment
;   Returns:
;       CF:     Set if drive is handled by this BIOS
;               Cleared if drive belongs to some other BIOS
;   Corrupts registers:
;       DI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
RamVars_IsDriveHandledByThisBIOS:
    xchg    di, ax                              ; Backup AX
    mov     ax, [RAMVARS.wDrvCntAndFirst]       ; Drive count to AL, First number to AH
    add     al, ah                              ; One past last drive to AL
    cmp     dl, al                              ; Above last supported?
    jae     SHORT .DriveNotHandledByThisBIOS
    cmp     dl, ah                              ; Below first supported?
    jb      SHORT .DriveNotHandledByThisBIOS
    xchg    ax, di
    stc
    ret
ALIGN JUMP_ALIGN
.DriveNotHandledByThisBIOS:
    xchg    ax, di
    clc
    ret


;--------------------------------------------------------------------
; Increments hard disk count to RAMVARS.
;
; RamVars_IncrementHardDiskCount
;   Parameters:
;       DL:     Drive number for new drive
;       DS:     RAMVARS segment
;   Returns:
;       Nothing
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
RamVars_IncrementHardDiskCount:
    inc     BYTE [RAMVARS.bDrvCnt]      ; Increment drive count to RAMVARS
    cmp     BYTE [RAMVARS.bFirstDrv], 0 ; First drive set?
    ja      SHORT .Return               ;  If so, return
    mov     [RAMVARS.bFirstDrv], dl     ; Store first drive number
ALIGN JUMP_ALIGN
.Return:
    ret


;--------------------------------------------------------------------
; RamVars_GetHardDiskCountFromBDAtoCX
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       CX:     Total hard disk count
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------   
ALIGN JUMP_ALIGN
RamVars_GetHardDiskCountFromBDAtoCX:
    push    es
    push    dx

    LOAD_BDA_SEGMENT_TO es, cx          ; Zero CX
    call    RamVars_GetCountOfKnownDrivesToDL
    MAX_U   dl, [es:BDA.bHDCount]
    mov     cl, dl

    pop     dx
    pop     es
    ret

;--------------------------------------------------------------------
; RamVars_GetCountOfKnownDrivesToDL
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       DL:     Total hard disk count
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------   
ALIGN JUMP_ALIGN
RamVars_GetCountOfKnownDrivesToDL:
    mov     dl, [RAMVARS.bFirstDrv]     ; Number for our first drive
    add     dl, [RAMVARS.bDrvCnt]       ; Our drives
    and     dl, 7Fh                     ; Clear HD bit for drive count
    ret


;--------------------------------------------------------------------
; RamVars_GetIdeControllerCountToCX
;   Parameters:
;       Nothing
;   Returns:
;       CX:     Number of IDE controllers to handle
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------   
ALIGN JUMP_ALIGN
RamVars_GetIdeControllerCountToCX:
    mov     cx, 1                   ; Assume lite mode (one controller)
    test    BYTE [cs:ROMVARS.wFlags], FLG_ROMVARS_FULLMODE
    jz      SHORT .Return
    mov     cl, [cs:ROMVARS.bIdeCnt]
ALIGN JUMP_ALIGN, ret
.Return:
    ret