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Enabling DMA Transactions

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[Applies to KMDF only]

If your framework-based driver handles I/O operations for DMA devices, your driver must enable the framework's DMA features for each DMA device. To enable these features, your driver's EvtDriverDeviceAdd or EvtDevicePrepareHardware callback function must:

  1. Call WdfDeviceSetAlignmentRequirement to specify the device's requirement for buffer alignment.

  2. Call WdfDmaEnablerCreate to specify the type of DMA operations (single packet or scatter/gather) and the maximum transfer size that the device supports. Starting in KMDF version 1.11, the framework supports system-mode DMA on System on a Chip (SoC)–based systems running on Windows 8 or later versions of the operating system.

  3. Call WdfDmaEnablerSetMaximumScatterGatherElements to specify the maximum number of elements that the device can support in a scatter/gather list, if the device supports scatter/gather operations.

The following code example from the PLX9x5x sample illustrates how to enable the framework's DMA features. This code appears in the Init.c file.

WDF_DMA_ENABLER_CONFIG   dmaConfig;

WdfDeviceSetAlignmentRequirement( DevExt->Device, PCI9656_DTE_ALIGNMENT_16 );
WDF_DMA_ENABLER_CONFIG_INIT( &dmaConfig,
                             WdfDmaProfileScatterGather64Duplex,
                             DevExt->MaximumTransferLength );
status = WdfDmaEnablerCreate( DevExt->Device,
                              &dmaConfig, 
                              WDF_NO_OBJECT_ATTRIBUTES,
                              &DevExt->DmaEnabler );

If your driver requires common buffers, the driver's EvtDriverDeviceAdd callback function typically sets them up. For more information about these buffers, see Using Common Buffers.

After a driver has called WdfDmaEnablerCreate, it can call WdfDmaEnablerWdmGetDmaAdapter to obtain pointers to WDM DMA_ADAPTER structures that the framework creates for the device's input and output directions. However, most framework-based drivers do not need to access these structures.