Descriptor-Based Sub-Modes; Loopback Sub-Mode - Analog Devices VisualDSP++ 5.0 Service Manual

Theory of Operation
of a descriptor. When directed to callback the client upon completion of
the descriptor, the client callback function is passed the following
arguments:
• The client handle. This is the client-supplied value provided in the
adi_dma_Open()
• Event ID. This value is
• Starting address of the data

Descriptor-Based Sub-Modes

When using the small or large model descriptor-based transfers, two
sub-modes (loopback and streaming) allow the client application greater
flexibility in processing descriptors. Each of these sub-modes can be used
independently or in combination. Each sub-mode is enabled or disabled
via the
adi_dma_Control()
sub-modes must enable them prior to enabling dataflow on the channel.
By default, both sub-modes are disabled.

Loopback Sub-Mode

The loopback sub-mode is controlled by the
command.
When loopback sub-mode is enabled (after the DMA manager has pro-
cessed the last descriptor in the chain of descriptors provided to a
channel), it automatically loops back to the first descriptor provided to the
channel. This effectively creates an infinite loop of descriptors as
illustrated in Figure
can provide the descriptors at initialization time, allow the DMA manager
to process the descriptors, and never need to resupply the DMA manager
with additional descriptors.
6-24
function.
ADI_DMA_EVENT_DESCRIPTOR_PROCESSED
function. Clients that want to use these
6-3. For example, with loopback sub-mode, the client
VisualDSP++ 5.0 Device Drivers and System
Services Manual for Blackfin Processors
ADI_DMA_CMD_SET_LOOPBACK
.