source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/AH15h_HSize.asm@ 371

; Project name  :   XTIDE Universal BIOS
; Description   :   Int 13h function AH=15h, Read Disk Drive Size.

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Int 13h function AH=15h, Read Disk Drive Size.
;
; AH15h_HandlerForReadDiskDriveSize
;   Parameters:
;       DL:     Translated Drive number
;       DS:DI:  Ptr to DPT (in RAMVARS segment)
;       SS:BP:  Ptr to IDEPACK
;   Returns with INTPACK:
;       If successful:
;           AH:     Hard Disk: 3 (Hard disk accessible)
;                   Floppy:    1 (Floppy disk, without change detection)
;           CX:DX:  Total number of sectors
;           CF:     0
;       If failed:
;           AH:     0 (Drive not present)
;           CX:DX:  0
;           CF:     1
;--------------------------------------------------------------------
AH15h_HandlerForReadDiskDriveSize:
%ifdef MODULE_SERIAL_FLOPPY
    mov     cl, 1                                       ; 1 = floppy disk, no change detection

    test    dl,dl                                       ; DO NOT store the sector count if this is a
    jns     .FloppyDrive                                ; floppy disk, some OS's depend on this not
                                                        ; happening for floppies in order to boot.
%endif

    call    AH15h_GetSectorCountToBXDXAX
    mov     [bp+IDEPACK.intpack+INTPACK.cx], dx         ; HIWORD to CX
    xchg    [bp+IDEPACK.intpack+INTPACK.dx], ax         ; LOWORD to DX, AL gets drive number

    xor     ah, ah
%ifdef MODULE_SERIAL_FLOPPY
    mov     cl, 3                                       ; 3 = Hard Disk Accessible
.FloppyDrive:

    call    Int13h_SetErrorCodeToBdaAndToIntpackInSSBPfromAH_ALHasDriveNumber   ; Store success to BDA and CF
    mov     [bp+IDEPACK.intpack+INTPACK.ah], cl
%else
    call    Int13h_SetErrorCodeToBdaAndToIntpackInSSBPfromAH    ; Store success to BDA and CF
    mov     BYTE [bp+IDEPACK.intpack+INTPACK.ah], 3
%endif

    jmp     Int13h_ReturnFromHandlerWithoutStoringErrorCode


;--------------------------------------------------------------------
; AH15h_GetSectorCountFromForeignDriveToDXAX:
; AH15h_GetSectorCountToBXDXAX:
;   Parameters:
;       DL:     Drive number (AH15h_GetSectorCountFromForeignDriveToDXAX only)
;       DS:     RAMVARS segment
;       DS:DI:  Ptr to DPT (AH15h_GetSectorCountToDXAX only)
;   Returns:
;       DX:AX:  Total sector count
;       BX:     Zero
;   Corrupts registers:
;       CX
;--------------------------------------------------------------------
AH15h_GetSectorCountFromForeignDriveToDXAX:
    mov     ah, GET_DRIVE_PARAMETERS
    call    Int13h_CallPreviousInt13hHandler
    jmp     SHORT ConvertAH08hReturnValuesToSectorCount

AH15h_GetSectorCountToBXDXAX:
    call    AH8h_GetDriveParameters
    ; Fall to ConvertAH08hReturnValuesToSectorCount

ConvertAH08hReturnValuesToSectorCount:
    call    Address_ExtractLCHSparametersFromOldInt13hAddress
    mov     al, bh      ; AL = Max head number
    inc     cx          ; Max cylinder number to cylinder count
    inc     ax          ; Max head number to head count (AH=8h returns max 254 so no overflow to AH)
    mul     bl          ; AX = Head count * Sectors per track
    mul     cx          ; DX:AX = Total sector count for AH=0xh transfer functions
    xor     bx, bx
    ret