By configuring the DMA to transfer data to one or more GPIO ports, it is possible to
create complex waveforms using tabular data stored in on-chip memory. Conversely,
using the DMA to periodically transfer data from one or more GPIO ports, it is
possible to sample complex waveforms and store the results in tabular form in on-
chip memory.
A more detailed description of the capability of each trigger, including resolution, range
of values, and so on, may be found in the periodic interrupt timer section.
22.4.2 DMA channels with no triggering capability
The other channels of the DMAMUX provide the normal routing functionality as
described in Modes of operation.
22.4.3 Always-enabled DMA sources
In addition to the peripherals that can be used as DMA sources, there are 6 additional
DMA sources that are always enabled. Unlike the peripheral DMA sources, where the
peripheral controls the flow of data during DMA transfers, the sources that are always
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.
Chapter 22 Direct Memory Access Multiplexer (DMAMUX)
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
Freescale Semiconductor, Inc. 343
To Next Page
Loading...
