Initialization/Application Information - STMicroelectronics SPC572L series Reference Manual

Direct Memory Access Multiplexer (DMAMUX)
enabled provide no such "throttling" of the data transfers. These sources are most useful in
the following cases:
•
Performing DMA transfers to/from GPIO—Moving data from/to one or more GPIO pins,
either unthrottled (that is, as fast as possible), or periodically (using the DMA triggering
capability).
•
Performing DMA transfers from memory to memory—Moving data from memory to
memory, typically as fast as possible, sometimes with software activation.
•
Performing DMA transfers from memory to the external bus, or vice-versa—Similar to
memory to memory transfers, this is typically done as quickly as possible.
•
Any DMA transfer that requires software activation—Any DMA transfer that should be
explicitly started by software.
In cases where software should initiate the start of a DMA transfer, an always-enabled DMA
source can be used to provide maximum flexibility. When activating a DMA channel via
software, subsequent executions of the minor loop require that a new start event be sent.
This can either be a new software activation, or a transfer request from the DMA channel
MUX. The options for doing this are:
•
Transfer all data in a single minor loop.
By configuring the DMA to transfer all of the data in a single minor loop (that is, major
loop counter = 1), no reactivation of the channel is necessary. The disadvantage to this
option is the reduced granularity in determining the load that the DMA transfer will
impose on the system. For this option, the DMA channel must be disabled in the DMA
channel MUX.
•
Use explicit software reactivation.
In this option, the DMA is configured to transfer the data using both minor and major
loops, but the processor is required to reactivate the channel by writing to the DMA
registers after every minor loop. For this option, the DMA channel must be disabled in
the DMA channel MUX.
•
Use an always-enabled DMA source.
In this option, the DMA is configured to transfer the data using both minor and major
loops, and the DMA channel MUX does the channel reactivation. For this option, the
DMA channel should be enabled and pointing to an "always enabled" source. Note that
the reactivation of the channel can be continuous (DMA triggering is disabled) or can
use the DMA triggering capability. In this manner, it is possible to execute periodic
transfers of packets of data from one source to another, without processor intervention.
20.5

Initialization/application information

This section provides instructions for initializing the DMA channel MUX.
20.5.1 Reset
The reset state of each individual bit is shown in
definition. In summary, after reset, all channels are disabled and must be explicitly enabled
before use.
20.5.2 Enabling and configuring sources
To enable a source with periodic triggering:
456/2058
Section 20.3: Memory map/register
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