Enabling DMA Transactions
[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:
Call WdfDeviceSetAlignmentRequirement to specify the device's requirement for buffer alignment.
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.
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.