source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/FindDPT.asm@ 201

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

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Finds pointer to first unused Disk Parameter Table.
;
; FindDPT_ForNewDriveToDSDI
;   Parameters:
;       DS:     RAMVARS segment
;   Returns:
;       DS:DI:  Ptr to first unused DPT
;   Corrupts registers:
;       DL
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FindDPT_ForNewDriveToDSDI:
    mov     dl, [RAMVARS.bFirstDrv]
    add     dl, [RAMVARS.bDrvCnt]
    ; Fall to FindDPT_ForDriveNumber


;--------------------------------------------------------------------
; Finds Disk Parameter Table for drive number.
; IDE Base Port address will be stored to RAMVARS if correct DPT is found.
;
; FindDPT_ForDriveNumber
;   Parameters:
;       DL:     Drive number
;       DS:     RAMVARS segment
;   Returns:
;       DS:DI:  Ptr to DPT
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
FindDPT_ForDriveNumber:
    push    dx
    xchg    di, ax  ; Save the contents of AX in DI

    mov     al, LARGEST_DPT_SIZE
    sub     dl, [RAMVARS.bFirstDrv]
    mul     dl
    add     ax, BYTE RAMVARS_size

    xchg    di, ax  ; Restore AX and put result in DI
    pop     dx
    ret

;--------------------------------------------------------------------
; Finds Disk Parameter Table for
; Master or Slave drive at wanted port.
;
; FindDPT_ToDSDIForIdeMasterAtPortDX
; FindDPT_ToDSDIForIdeSlaveAtPortDX
;   Parameters:
;       DX:     IDE Base Port address
;       DS:     RAMVARS segment
;   Returns:
;       DL:     Drive number (if DPT found)
;       DS:DI:  Ptr to DPT
;       CF:     Set if wanted DPT found
;               Cleared if DPT not found
;   Corrupts registers:
;       SI
;
; Converted to macros since there is only once call site for each of these
;
;--------------------------------------------------------------------
    
%macro FindDPT_ToDSDIForIdeMasterAtPortDX 0
    mov     si, IterateToMasterAtPortCallback
    call    IterateAllDPTs
%endmacro

%macro FindDPT_ToDSDIForIdeSlaveAtPortDX 0
    mov     si, IterateToSlaveAtPortCallback
    call    IterateAllDPTs
%endmacro

        
;--------------------------------------------------------------------
; Iteration callback for finding DPT using
; IDE base port for Master or Slave drive.
;
; IterateToSlaveAtPortCallback
; IterateToMasterAtPortCallback
;   Parameters:
;       CH:     Drive number
;       DX:     IDE Base Port address
;       DS:DI:  Ptr to DPT to examine
;   Returns:
;       DL:     Drive number if correct DPT
;       CF:     Set if wanted DPT found
;               Cleared if wrong DPT
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
IterateToSlaveAtPortCallback:
    test    BYTE [di+DPT.bFlagsLow], FLGL_DPT_SLAVE ; Clears CF
    jnz     SHORT CompareBasePortAddress
    ret     ; Wrong DPT

ALIGN JUMP_ALIGN
IterateToMasterAtPortCallback:
    test    BYTE [di+DPT.bFlagsLow], FLGL_DPT_SLAVE
    jnz     SHORT ReturnWrongDPT                ; Return if slave drive

CompareBasePortAddress:
    push    bx
    eMOVZX  bx, BYTE [di+DPT.bIdevarsOffset]    ; CS:BX now points to IDEVARS
    cmp     dx, [cs:bx+IDEVARS.wPort]           ; Wanted port?
    pop     bx
    jne     SHORT ReturnWrongDPT
    mov     dl, ch                              ; Return drive number in DL

ReturnRightDPT:
    stc                                         ; Set CF since wanted DPT
    ret


;--------------------------------------------------------------------
; IterateToDptWithFlagsHighSet:
;   Parameters:
;       DS:DI:  Ptr to DPT to examine
;       AL:     Bit in bFlagsHigh to test
;   Returns:
;       CF:     Set if wanted DPT found
;               Cleared if wrong DPT
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
IterateToDptWithFlagsHighSet:
    test    BYTE [di+DPT.bFlagsHigh], al    ; Clears CF (but we need the clc below anyway callers above)
    jnz     SHORT ReturnRightDPT

ReturnWrongDPT:
    clc                                     ; Clear CF since wrong DPT
    ret

;--------------------------------------------------------------------
; FindDPT_ToDSDIforInterruptInService
; 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, AX, BX (for SerialDevice only)
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
        
%ifdef MODULE_SERIAL
FindDPT_ToDSDIforSerialDevice:  
    mov     al, FLGH_DPT_SERIAL_DEVICE

    SKIP2B  bx
%endif
        
; do not align due to SKIP2B above
FindDPT_ToDSDIforInterruptInService:
    mov     al, FLGH_DPT_INTERRUPT_IN_SERVICE

    mov     si, IterateToDptWithFlagsHighSet
    ; Fall to IterateAllDPTs

;--------------------------------------------------------------------
; Iterates all Disk Parameter Tables.
;
; IterateAllDPTs
;   Parameters:
;       AX,BX,DX:   Parameters to callback function
;       CS:SI:      Ptr to callback function
;       DS:         RAMVARS segment
;   Returns:
;       DS:DI:      Ptr to wanted DPT (if found)
;       CF:         Set if wanted DPT found
;                   Cleared if DPT not found, or no DPTs present
;   Corrupts registers:
;       Nothing unless corrupted by callback function
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
IterateAllDPTs:
    push    cx
    mov     cx, [RAMVARS.wDrvCntAndFirst]
    jcxz    .NotFound                   ; Return if no drives
    mov     di, RAMVARS_size            ; Point DS:DI to first DPT
ALIGN JUMP_ALIGN
.LoopWhileDPTsLeft:
    call    si                          ; Is wanted DPT?
    jc      SHORT .AllDptsIterated      ;  If so, return
    inc     ch                          ; Increment drive number
    add     di, BYTE LARGEST_DPT_SIZE   ; Point to next DPT
    dec     cl                          ; Decrement drives left
    jnz     SHORT .LoopWhileDPTsLeft
.NotFound:      
    clc                                 ; Clear CF since DPT not found
ALIGN JUMP_ALIGN
.AllDptsIterated:
    pop     cx
    ret