Using Bus-Master DMA

Drivers of bus-master DMA devices can use the following kinds of system-supplied DMA support:

• Packet-based DMA if the bus-master adapter allows the driver to determine when a DMA transfer operation is done and/or when to begin another transfer operation for a given IRP. See Using Packet-Based Bus-Master DMA for details.

• Common-buffer DMA (also called continuous DMA) if the bus-master adapter does not provide a way for the driver to determine readily when a transfer operation will begin or when a transfer is complete, or if a single buffer area is used continuously or repeatedly for DMA transfers. See Using Common-Buffer Bus-Master DMA for details.

Depending on the nature of the bus-master adapter, some drivers use packet-based DMA exclusively, some use common-buffer DMA exclusively, and some use both. For example, the driver of a bus-master adapter that uses a mailbox scheme to communicate status information and commands might use a common buffer for the mailboxes shared between the driver and its adapter, together with packet-based DMA for data transfers.