source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/AH8h_HParams.asm @ 148

; Project name  :   XTIDE Universal BIOS
; Description   :   Int 13h function AH=8h, Read Disk Drive Parameters.

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Int 13h function AH=8h, Read Disk Drive Parameters.
;
; AH8h_HandlerForReadDiskDriveParameters
;   Parameters:
;       DL:     Translated Drive number
;       DS:DI:  Ptr to DPT (in RAMVARS segment)
;       SS:BP:  Ptr to INTPACK
;   Returns with INTPACK in SS:BP:
;       CH:     Maximum cylinder number, bits 7...0
;       CL:     Bits 7...6: Cylinder number bits 9...8
;               Bits 5...0: Maximum sector number (1...63)
;       DH:     Maximum head number (0...255)
;       DL:     Number of drives
;       AH:     Int 13h/40h floppy return status
;       CF:     0 if successfull, 1 if error
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
AH8h_HandlerForReadDiskDriveParameters:
    call    RamVars_IsDriveHandledByThisBIOS
    jnc     SHORT .GetDriveParametersForForeignHardDiskInDL
    call    AH8h_GetDriveParameters
    jmp     SHORT .ReturnAfterStoringValuesToIntpack

.GetDriveParametersForForeignHardDiskInDL:
    call    Int13h_CallPreviousInt13hHandler
    jc      SHORT .ReturnErrorFromPreviousInt13hHandler
    call    RamVars_GetCountOfKnownDrivesToDL
.ReturnAfterStoringValuesToIntpack:
    mov     [bp+INTPACK.cx], cx
    mov     [bp+INTPACK.dx], dx
    xor     ah, ah
.ReturnErrorFromPreviousInt13hHandler:
    jmp     Int13h_ReturnFromHandlerAfterStoringErrorCodeFromAH


;--------------------------------------------------------------------
; Returns L-CHS parameters for drive and total hard disk count.
;
; AH8h_GetDriveParameters
;   Parameters:
;       DS:DI:  Ptr to DPT (in RAMVARS segment)
;   Returns:
;       CH:     Maximum cylinder number, bits 7...0
;       CL:     Bits 7...6: Cylinder number bits 9...8
;               Bits 5...0: Maximum sector number (1...63)
;       DH:     Maximum head number (0...255)
;       DL:     Number of drives
;   Corrupts registers:
;       AX, BX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
AH8h_GetDriveParameters:
    call    AccessDPT_GetLCHSfromPCHS   ; AX=sectors, BX=cylinders, DX=heads
    ; Fall to .PackReturnValues

;--------------------------------------------------------------------
; Packs L-CHS values to INT 13h, AH=08h return values.
;
; .PackReturnValues
;   Parameters:
;       AX:     Number of L-CHS sectors per track (1...63)
;       BX:     Number of L-CHS cylinders available (1...1024)
;       DX:     Number of L-CHS heads (1...256)
;       DS:     RAMVARS segment
;   Returns:
;       CH:     Maximum cylinder number, bits 7...0
;       CL:     Bits 7...6: Cylinder number bits 9...8
;               Bits 5...0: Maximum sector number (1...63)
;       DH:     Maximum head number (0...255)
;       DL:     Number of drives
;   Corrupts registers:
;       AX, BX
;--------------------------------------------------------------------
.PackReturnValues:
    dec     bx                      ; Cylinder count to last cylinder
    dec     dx                      ; Head count to max head number
    mov     dh, dl                  ; Max head number to DH
    mov     ch, bl                  ; Cylinder bits 7...0 to CH
    mov     cl, bh                  ; Cylinder bits 9...8 to CL
    eROR_IM cl, 2                   ; Cylinder bits 9...8 to CL bits 7...6
    or      cl, al                  ; Sectors per track to CL bits 5...0
    jmp     RamVars_GetCountOfKnownDrivesToDL