PDX_TRANSFER callback function (dxmini.h)
The DxTransfer callback function informs the driver to bus master data from a surface to the buffer specified in the memory descriptor list (MDL).
Syntax
PDX_TRANSFER PdxTransfer;
DWORD PdxTransfer(
PVOID unnamedParam1,
PDDTRANSFERININFO unnamedParam2,
PDDTRANSFEROUTINFO unnamedParam3
)
{...}
Parameters
unnamedParam1
Points to the miniport driver's device extension.
unnamedParam2
Points to a DDTRANSFERININFO structure that contains the transfer information for the surface.
unnamedParam3
Points to a DDTRANSFEROUTINFO structure that contains the polarity of the field being captured.
Return value
DxTransfer returns DX_OK if it succeeds; otherwise, it returns one of the following error values:
Remarks
The MDL is defined in WDM documentation.
As shown in the following code sample, the video miniport driver can use the pointer to the MDL in the lpDestMDL member of the DDTRANSFERININFO structure at the TransferInInfo parameter to bus master data to the physical memory pages that make up a scattered buffer:
DWORD
DxTransfer(
DEVICE_EXT *pDeviceExt,
PDDTRANSFERININFO pTransferInInfo,
PDDTRANSFEROUTINFO pTransferOutInfo
)
{
PMDL pMdl;
UINT uiNbPages;
PPFN_NUMBER pPages;
PVOID MappedSystemVa;
ULONG ByteCount;
pMdl = pTransferInInfo->lpDestMDL;
MappedSystemVa = MmGetMdlVirtualAddress(pMdl);
ByteCount = MmGetMdlByteCount(pMdl);
uiNbPages = ADDRESS_AND_SIZE_TO_SPAN_PAGES(MappedSystemVa,
ByteCount);
pPages = MmGetMdlPfnArray(pMdl)
for (i=0; i<uiNbPages; i++) {
//
// Transfer to page[i]
//
pPages[i];
}
}
See the ADDRESS_AND_SIZE_TO_SPAN_PAGES, MmGetMdlByteCount, MmGetMdlPfnArray, and MmGetMdlVirtualAddress kernel-mode macros for more information.
DxTransfer is called at hardware interrupt time. This means the driver cannot wait for a previous bus master to complete and it cannot call any functions that are not safe to call at interrupt time (that is, most of them).
In addition, the driver should not fail the call just because the hardware is currently busy. Instead, the driver should maintain an internal queue.
Requirements
| Requirement | Value |
|---|---|
| Target Platform | Desktop |
| Header | dxmini.h (include Dxmini.h) |