Article: Q83012
Product(s): Microsoft Windows Device Driver Kit
Version(s): 3.0,3.1
Operating System(s):
Keyword(s):
Last Modified: 03-NOV-1999
-------------------------------------------------------------------------------
The information in this article applies to:
- Microsoft Windows Device Development Kit (DDK) for Windows, versions 3.0, 3.1
-------------------------------------------------------------------------------
SUMMARY
=======
VADMAD, the Virtual Auto-Initialize Direct Memory Access Device, is provided
with the Windows Multimedia Device Development Kit version 1.0, and the
Multimedia Extensions to Windows version 1.0, to allow devices that use
auto-initialize DMA to function properly under Windows 3.0.
However, under Windows version 3.1, the VDMAD (Virtual DMA Device) supports an
auto-initialize DMA transfer, without using VADMAD.
Do not use VADMAD with Windows 3.1 because it conflicts with VDMAD.
The remainder of this article describes how an application can perform auto-
initialize DMA transfers under Windows 3.0 and under Windows 3.1.
MORE INFORMATION
================
Under Windows version 3.1, auto-initialize DMA is performed using the same
method as under MS-DOS: set the auto-initialize bit in the mode register and
perform the transfer.
Under Windows 3.0, the application must call VADMAD to set the auto- initialize
bit of the DMA mode register.
If the VADMAD driver is installed, the GetVADMADEntry function, listed below,
returns its address in ES:DI. If INT 2Fh returns 0 in ES, VADMAD is not
installed, and attempts to call the address will cause a general protection
fault (GP fault).
VADMAD_Entry dd ?
cProc GetVADMADEntry <NEAR,PASCAL,PUBLIC><si,di>
xor di,di ; Clear DI
mov es,di ; Clear ES
mov ax,1684h ; Get device entry
mov bx,0444h ; VADMAD Device
int 2f ; Get function entry
mov word ptr [VADMAD_ENTRY],di ; Save entry point
mov word ptr [VADMAD_ENTRY+2],es
cEnd
Once the VADMAD address is available, set the DMA mode using the following code:
push dx ; Save DX
mov dx,VADMAD_Service ; Set VADMAD operation
call VADMAD_Entry ; Set mode or channel
out 0Bh,al ; Out to mode register
pop dx ; Restore DX
The values for the VADMAD_Service are defined as follows:
0: Set the VADMAD mode (put the desired mode into the AX register)
1: Set the VADMAD channel (put the desired channel into the AX register)
Two calls to the VADMAD_Entry are required: one to set the mode and one to set
the channel.
Under Windows 3.1, set the mode by modifying the mode register, as follows:
mov al,01010100b ; Auto-Initialize, Write, Channel 0
out 0bh,al ; Send the data to the DMA mode register.
An application can use the same procedure to program channels 4 through 7, which
are 16-bit channels; channels 0 through 3 are 8-bit channels. To program
channels 4 through 7, use port D6h rather than 0Bh.
Additional query words: 3.00 3.10
======================================================================
Keywords :
Technology : kbAudDeveloper kbWin3xSearch kbWinDDKSearch kbWinDDK300 kbWinDDK310
Version : :3.0,3.1
=============================================================================