K60P100M100SF2RM Datasheet, PDF (424/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional description
20.4.2 DMA channels with no triggering capability
The other channels of the DMA MUX provide the normal routing functionality as
described in Modes of operation.
20.4.3 "Always enabled" DMA sources
In addition to the peripherals that can be used as DMA sources, there are 10 additional
DMA sources that are "always enabled". Unlike the peripheral DMA sources, where the
peripheral controls the flow of data during DMA transfers, the "always enabled" sources
provide no such "throttling" of the data transfers. These sources are most useful in the
following cases:
• Doing DMA transfers to/from GPIO—Moving data from/to one or more GPIO pins,
either un-throttled (that is as fast as possible), or periodically (using the DMA
triggering capability).
• Doing DMA transfers from memory to memory—Moving data from memory to
memory, typically as fast as possible, sometimes with software activation.
• Doing 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 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 re-activation of the
channel is necessary. The disadvantage to this option is the reduced granularity in
determining the load that the DMA transfer will incur on the system. For this option,
the DMA channel should be disabled in the DMA channel MUX.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
424
Freescale Semiconductor, Inc.