source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/FindDPT.asm@ 263

; Project name  :   XTIDE Universal BIOS
; Description   :   Functions for finding Disk Parameter Table.

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Checks if drive is handled by this BIOS, and return DPT pointer.
;
; FindDPT_ForDriveNumberInDL        
;   Parameters:
;       DL:     Drive number
;       DS:     RAMVARS segment
;   Returns:
;       CF:     Cleared if drive is handled by this BIOS
;               Set if drive belongs to some other BIOS
;       DI:     DPT Pointer if drive is handled by this BIOS
;               Zero if drive belongs to some other BIOS
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FindDPT_ForDriveNumberInDL:     
    xchg    di, ax                              ; Save the contents of AX in DI

; 
; Check Our Hard Disks
;
    mov     ax, [RAMVARS.wDrvCntAndFirst]       ; Drive count to AH, First number to AL
    add     ah, al                              ; One past last drive to AH

%ifdef MODULE_SERIAL_FLOPPY
    cmp     dl, ah                              ; Above last supported?
    jae     SHORT .HardDiskNotHandledByThisBIOS
        
    cmp     dl, al                              ; Below first supported?
    jae     SHORT .CalcDPTForDriveNumber

ALIGN JUMP_ALIGN                
.HardDiskNotHandledByThisBIOS:  
;
; Check Our Floppy Disks
; 
    call    RamVars_UnpackFlopCntAndFirstToAL
    cbw                                         ; normally 0h, could be ffh if no drives present
    adc     ah, al                              ; if no drives present, still ffh (ffh + ffh + 1 = ffh)
    js      SHORT .DiskIsNotHandledByThisBIOS
    cmp     ah, dl                              ; Check second drive if two, first drive if only one
    jz      SHORT .CalcDPTForDriveNumber
    cmp     al, dl                              ; Check first drive in all cases, redundant but OK to repeat
    jnz     SHORT .DiskIsNotHandledByThisBIOS           
%else
    cmp     dl, ah                              ; Above last supported?     
    jae     SHORT .DiskIsNotHandledByThisBIOS
        
    cmp     dl, al                              ; Below first supported?
    jb      SHORT .DiskIsNotHandledByThisBIOS           
%endif
    ; fall-through to CalcDPTForDriveNumber

;--------------------------------------------------------------------
; Finds Disk Parameter Table for drive number.
; Note intended to be called except by FindDPT_ForDriveNumber
;
; CalcDPTForDriveNumber
;   Parameters:
;       DL:     Drive number
;       DS:     RAMVARS segment
;       DI:     Saved copy of AX from entry at FindDPT_ForDriveNumber
;   Returns:
;       DS:DI:  Ptr to DPT
;       CF:     Clear
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.CalcDPTForDriveNumber:
    push    dx

%ifdef MODULE_SERIAL_FLOPPY
    mov     ax, [RAMVARS.wDrvCntAndFirst]
        
    test    dl, dl
    js      .harddisk

    call    RamVars_UnpackFlopCntAndFirstToAL
    add     dl, ah                      ; add in end of hard disk DPT list, floppies start immediately after
        
ALIGN JUMP_ALIGN                
.harddisk:
    sub     dl, al                      ; subtract off beginning of either hard disk or floppy list (as appropriate)
%else
    sub     dl, [RAMVARS.bFirstDrv]     ; subtract off beginning of hard disk list
%endif

.CalcDPTForNewDrive:                
    mov     al, LARGEST_DPT_SIZE
        
    mul     dl
    add     ax, BYTE RAMVARS_size       ; Clears CF (will not oveflow)

    pop     dx

    xchg    di, ax                      ; Restore AX from entry at FindDPT_ForDriveNumber, put DPT pointer in DI
    ret

ALIGN JUMP_ALIGN        
.DiskIsNotHandledByThisBIOS:            
;
; Drive not found...
;
    xor     ax, ax                              ; Clear DPT pointer
    stc                                         ; Is not supported by our BIOS      
        
    xchg    di, ax                              ; Restore AX from save at top
    ret

;--------------------------------------------------------------------
; Finds pointer to first unused Disk Parameter Table.
; Should only be used before DetectDrives is complete (not valid after this time).
;
; FindDPT_ForNewDriveToDSDI
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       DS:DI:  Ptr to first unused DPT
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FindDPT_ForNewDriveToDSDI:
    push    dx
        
%ifdef MODULE_SERIAL_FLOPPY
    mov     dx, [RAMVARS.wDrvCntAndFlopCnt]
    add     dl, dh
%else
    mov     dl, [RAMVARS.bDrvCnt]
%endif
        
    jmp     short FindDPT_ForDriveNumberInDL.CalcDPTForNewDrive

;--------------------------------------------------------------------
; IterateToDptWithFlagsHighInBL
;   Parameters:
;       DS:DI:  Ptr to DPT to examine
;       BL:     Bit(s) to test in DPT.bFlagsHigh 
;   Returns:
;       CF:     Clear if wanted DPT found
;               Set if wrong DPT
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
IterateToDptWithFlagsHighInBL:      
    test    BYTE [di+DPT.bFlagsHigh], bl        ; Clears CF
    jnz     SHORT .ReturnRightDPT
    stc
.ReturnRightDPT:        
    ret

;--------------------------------------------------------------------
; FindDPT_ToDSDIforSerialDevice
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       DS:DI:  Ptr to DPT
;       CF:     Set if wanted DPT found
;               Cleared if DPT not found
;   Corrupts registers:
;       SI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN        
FindDPT_ToDSDIforSerialDevice:          
    mov     bl, FLGH_DPT_SERIAL_DEVICE
; fall-through
                
;--------------------------------------------------------------------
; FindDPT_ToDSDIforFlagsHigh
;   Parameters:
;       DS:     RAMVARS segment
;       BL:     Bit(s) to test in DPT.bFlagsHigh
;   Returns:
;       DS:DI:  Ptr to DPT
;       CF:     Set if wanted DPT found
;               Cleared if DPT not found
;   Corrupts registers:
;       SI
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FindDPT_ToDSDIforFlagsHighInBL:     
    mov     si, IterateToDptWithFlagsHighInBL
    ; Fall to IterateAllDPTs

;--------------------------------------------------------------------
; Iterates all Disk Parameter Tables.
;
; IterateAllDPTs
;   Parameters:
;       AX,BX,DX:   Parameters to callback function
;       CS:SI:      Ptr to callback function
;                   Callback routine should return CF=clear if found
;       DS:         RAMVARS segment
;   Returns:
;       DS:DI:      Ptr to wanted DPT (if found)
;                   If not found, points to first empty DPT
;       CF:         Clear if wanted DPT found
;                   Set if DPT not found, or no DPTs present
;   Corrupts registers:
;       Nothing unless corrupted by callback function
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
IterateAllDPTs:
    push    cx

    mov     di, RAMVARS_size            ; Point DS:DI to first DPT
        
    mov     cl, [RAMVARS.bDrvCnt]
    xor     ch, ch                      ; Clears CF  
        
    jcxz    .NotFound                   ; Return if no drives
        
ALIGN JUMP_ALIGN
.LoopWhileDPTsLeft:
    call    si                          ; Is wanted DPT?
    jnc     SHORT .Found                ;  If so, return
    add     di, BYTE LARGEST_DPT_SIZE   ; Point to next DPT
    loop    .LoopWhileDPTsLeft

ALIGN JUMP_ALIGN
.NotFound:
    stc

ALIGN JUMP_ALIGN
.Found:
    pop     cx
    ret