HPAVC/HPAVC CD-ROM.iso/PCGPEV10.ZIP/DMA_VLA.TXT

Text File | 1994-05-10 | 14KB | 507 lines

─────────────────────────────────────────────────────────────────────────────
                       INTRO TO DMA by Draeden of VLA
─────────────────────────────────────────────────────────────────────────────


    DMA means Direct Memory Access.  You probably already know where and
why you use it, so I'll skip right down to the dirty stuff.  This all
should speak for it's self, so... Enjoy.

    Draeden /VLA

─────────────────────────────────────────────────────────────────────────────

    To do a DMA transfer, you need to know a few things:

        1)  Address of the memory to access

        2)  Length of data to read/write

    This can all be put into a structure:

STRUC DMAInfo
    Page        db  ?
    Offset      dw  ?
    Length      dw  ?
ENDS

    Page is the highest 4 bits of the absolute 20 bit address of the memory
location.  Note that DMA transfers CANNOT cross 64k page boundries.

    The Length is actually LENGTH-1; sending in a 0 will move 1 byte,
sending a 0FFFFh will move 64k.

    ─────────────────────────────────────────────────────────────────────
    ; IN: DX:AX = segment/offset address of memory area
    ;
    ;OUT: DH = Page (0-F)  (DL is destroyed)
    ;     AX = Offset
    ─────────────────────────────────────────────────────────────────────
PROC MakePage
    push    bx

    mov     bl,dh
    shr     bl,4    ;isolate upper 4 bits of segment

    shl     dx,4    ;make segment into ABS address
    add     ax,dx   ;add the offset and put it in AX
    adc     bl,0    ;complete the addition

    mov     dh,bl   ;put the PAGE where it goes

    pop     bx      ; DH:AX is now the PAGE:OFFSET address
    ret
ENDP

─────────────────────────────────────────────────────────────────────────────
    Programming DMA channels 0 thru 3
─────────────────────────────────────────────────────────────────────────────
    There are 3 ports that are DMA channel specific:

        1) The Page register
        2) The DMA count (length) register
        3) The memory address (offset register)

    They are as follows:

DMACH   PAGE    ADDRESS  LENGTH

 0       87h       0       1

 1       83h       2       3

 2       81h       4       5

 3       82h       6       7


    And now some general registers:

 DMA Mask Register:  0Ah
────────────────────────
        bit 7 - 3 = 0  Reserved

            bit 2 = 0  clear mask
                  = 1  set mask

       bits 1 - 0 = 00 Select channel 0
                  = 01 select channel 1
                  = 10 select channel 2
                  = 11 select channel 3

       USE: You must set the mask of the channel before you
            can reprogram it.

 DMA Mode Register:  0Bh
────────────────────────
        bit 7 - 6 = 00 Demand mode
                  = 01 Signal mode
                  = 10 Block mode
                  = 11 Cascade mode

        bit 5 - 4 = 0  Reserved

        bit 3 - 2 = 00 Verify operation
                  = 01 Write operation
                  = 10 Read operation
                  = 11 Reserved

       bits 1 - 0 = 00 Select channel 0
                  = 01 select channel 1
                  = 10 select channel 2
                  = 11 select channel 3

       USE: Tell the DMAC what to do. Common modes are:

            48h (Read operation, Signal mode)
                Used to read data from host memory and send to whomever
                polls it.

            44h (Write operation, Signal mode)
                Used to write data taken from a device to memory.

DMA clear byte ptr:  0Ch
────────────────────────
       USE: Send a zero to reset the internal ptrs



    WHAT TO DO:
────────────────────────

    1) Set the Mask bit for the channel

        mov     al,4
        add     al,[DMA_Channel]
        out     0ah,al

    2) Clear Byte Ptr

        sub     al,al
        out     0Ch,al

    3) Set the DMA transfer mode

        mov     al,48h                  ;MODE output (read)
        add     al,[DMA_Channel]
        out     0Bh,al

    4) Set the memory ADDRESS and LENGTH

        ;        AX = offset
        ;        CX = Length
        ;[DMA_Base] = port # of memory address

        mov     dx,[DMA_Base]
        out     dx,al                   ;send lower byte address
        mov     al,ah
        out     dx,al                   ;send high byte address

        inc     dl                  ;point to Count port
        mov     al,cl
        out     dx,al                   ;send low byte length
        mov     al,ch
        out     dx,al                   ;send high byte length

    5) Set the DMA page

        ; AL = Page

        mov     dx,[Dma_Page]
        out     dx,al                   ; write the Page

    6) Clear DMA mask bit

        mov     al,[byte DMA_Channel]
        out     0Ah,al                  ; port 0Ah, DMA-1 mask reg bit

    7) Program the other device that is going to use the DMA output/input


    ─────────────────────────────────────────────────────────────────────
    ; This routine programs the DMAC for channels 0-3
    ;
    ; IN: [DMA_Channel], [DMAbaseAdd], [DMApageReg] must be setup
    ;       [DAMBaseAdd] =  Memory Address port
    ;
    ;     dh = mode
    ;     ax = address
    ;     cx = length
    ;     dl = page
    ─────────────────────────────────────────────────────────────────────
PROC Prog_DMA03 NEAR
        push    bx
        mov     bx,ax

        mov     al,4
        add     al,[DMA_Channel]
        out     0Ah,al          ; mask reg bit

        sub     al,al
        out     0Ch,al          ; clr byte ptr

        mov     al,dh
        add     al,[DMA_Channel]
        out     0Bh,al          ; set mode reg

        push    dx

        mov     dx,[DMAbaseAdd]
        mov     al,bl
        out     dx,al           ; set base address low
        mov     al,bh
        out     dx,al           ; set base address high

        inc     dx              ;point to length
        mov     al,cl
        out     dx,al           ; set length low
        mov     al,ch
        out     dx,al           ; set length high

        pop     dx

        mov     al,dl
        mov     dx,[DmaPageReg]
        out     dx,al           ; set DMA page reg

        mov     al,[DMA_Channel]
        out     0Ah,al          ; unmask (activate) dma channel
        pop     bx
        ret
ENDP

─────────────────────────────────────────────────────────────────────────────
─────────────────────────────────────────────────────────────────────────────
    Programming DMA channels 4 thru 7
─────────────────────────────────────────────────────────────────────────────
─────────────────────────────────────────────────────────────────────────────

    Again, there are 3 ports that are DMA channel specific:

        1) The Page register
        2) The DMA count (length) register
        3) The memory address (offset register

    They are as follows:

DMACH   PAGE    ADDRESS  LENGTH

 4       8Fh      C0h      C2h

 5       8Bh      C4h      C6h

 6       89h      C8h      CAh

 7       8Ah      CCh      CEh


    And now some general registers:

 DMA Mask Register: 0D4h
────────────────────────
        bit 7 - 3 = 0  Reserved

            bit 2 = 0  clear mask
                  = 1  set mask

       bits 1 - 0 = 00 Select channel 4
                  = 01 select channel 5
                  = 10 select channel 6
                  = 11 select channel 7

       USE: You must set the mask of the channel before you
            can reprogram it.

 DMA Mode Register: 0D6h
────────────────────────
        bit 7 - 6 = 00 Demand mode
                  = 01 Signal mode
                  = 10 Block mode
                  = 11 Cascade mode

        bit 5 - 4 = 0  Reserved

        bit 3 - 2 = 00 Verify operation
                  = 01 Write operation
                  = 10 Read operation
                  = 11 Reserved

       bits 1 - 0 = 00 Select channel 4
                  = 01 select channel 5
                  = 10 select channel 6
                  = 11 select channel 7

       USE: Tell the DMAC what to do. Common modes are:

            48h (Read operation, Signal mode)
                Used to read data from host memory and send to whomever
                polls it.

            44h (Write operation, Signal mode)
                Used to write data taken from a device to memory.

DMA clear byte ptr: 0D8h
────────────────────────
       USE: Send a zero to reset the internal ptrs


    WHAT TO DO: (exactly the same thing, just different io PORTs)
────────────────────────

    1) Set the Mask bit for the channel

        mov     al,[DMA_Channel]    ;because the DMA's are 4-7, bit #3
        out     0D4h,al             ; is already set

    2) Clear Byte Ptr

        sub     al,al
        out     0D8h,al

    3) Set the DMA transfer mode

        mov     al,[DMA_Channel]
        sub     al,4
        or      al,48h                  ;MODE output (read)
        out     0D6h,al

    4) Set the memory ADDRESS and LENGTH

        ;        AX = offset
        ;        CX = Length
        ;[DMA_Base] = port # of memory address

        mov     dx,[DMA_Base]
        out     dx,al                   ;send lower byte address
        mov     al,ah
        out     dx,al                   ;send high byte address

        add     dl,2                ;point to Count port (seperated by 2)
        mov     al,cl
        out     dx,al                   ;send low byte length
        mov     al,ch
        out     dx,al                   ;send high byte length

    5) Set the DMA page

        ; AL = Page

        mov     dx,[Dma_Page]
        out     dx,al                   ; write the Page

    6) Clear DMA mask bit

        mov     al,[byte DMA_Channel]
        and     al,00000011b
        out     0d4h,al                 ; port 0Ah, DMA-1 mask reg bit

    7) Program the other device that is going to use the DMA output/input


    ─────────────────────────────────────────────────────────────────────
    ; This routine programs the DMAC for channels 4-7
    ;
    ; IN: [DMA_Channel], [DMAbaseAdd], [DMApageReg] must be setup
    ;       [DAMBaseAdd] =  Memory Address port
    ;
    ;     dh = mode
    ;     ax = address
    ;     cx = length
    ;     dl = page
    ─────────────────────────────────────────────────────────────────────
PROC Prog_DMA47 NEAR
        push    bx
        mov     bx,ax

        mov     al,[DMA_Channel]
        out     0D4h,al         ; mask reg bit

        sub     al,al
        out     0D8h,al         ; clr byte ptr

        mov     al,[DMA_Channel]
        sub     al,4
        add     al,dh
        out     0D6h,al         ; set mode reg

        push    dx

        mov     dx,[DMAbaseAdd]
        mov     al,bl
        out     dx,al           ; set base address low
        mov     al,bh
        out     dx,al           ; set base address high

        add     dl,2            ;point to length
        mov     al,cl
        out     dx,al           ; set length low
        mov     al,ch
        out     dx,al           ; set length high

        pop     dx

        mov     al,dl
        mov     dx,[DmaPageReg]
        out     dx,al           ; set DMA page reg

        mov     al,[DMA_Channel]
        and     al,00000011b
        out     0D4h,al         ; unmask (activate) dma channel
        pop     bx
        ret
ENDP

    ─────────────────────────────────────────────────────────────────────
    ; This routine programs the DMAC for channels 0-7
    ;
    ; IN: [DMA_Channel], [DMAbaseAdd], [DMApageReg] must be setup
    ;       [DAMBaseAdd] =  Memory Address port
    ;
    ;     dh = mode
    ;     ax = address
    ;     cx = length
    ;     dl = page
    ─────────────────────────────────────────────────────────────────────
PROC Prog_DMA NEAR
        push    bx
        mov     bx,ax

        cmp     [DMA_Channel],4
        jb      @@DoDMA03

        mov     al,[DMA_Channel]
        out     0D4h,al         ; mask reg bit

        sub     al,al
        out     0D8h,al         ; clr byte ptr

        mov     al,[DMA_Channel]
        sub     al,4
        add     al,dh
        out     0D6h,al         ; set mode reg

        push    dx

        mov     dx,[DMAbaseAdd]
        mov     al,bl
        out     dx,al           ; set base address low
        mov     al,bh
        out     dx,al           ; set base address high

        add     dl,2            ;point to length
        mov     al,cl
        out     dx,al           ; set length low
        mov     al,ch
        out     dx,al           ; set length high

        pop     dx

        mov     al,dl
        mov     dx,[DmaPageReg]
        out     dx,al           ; set DMA page reg

        mov     al,[DMA_Channel]
        and     al,00000011b
        out     0D4h,al         ; unmask (activate) dma channel
        pop     bx
        ret

@@DoDMA03:
        mov     al,4
        add     al,[DMA_Channel]
        out     0Ah,al          ; mask reg bit

        sub     al,al
        out     0Ch,al          ; clr byte ptr

        mov     al,dh
        add     al,[DMA_Channel]
        out     0Bh,al          ; set mode reg

        push    dx

        mov     dx,[DMAbaseAdd]
        mov     al,bl
        out     dx,al           ; set base address low
        mov     al,bh
        out     dx,al           ; set base address high

        inc     dx              ;point to length
        mov     al,cl
        out     dx,al           ; set length low
        mov     al,ch
        out     dx,al           ; set length high

        pop     dx

        mov     al,dl
        mov     dx,[DmaPageReg]
        out     dx,al           ; set DMA page reg

        mov     al,[DMA_Channel]
        out     0Ah,al          ; unmask (activate) dma channel
        pop     bx
        ret
ENDP