DMA Channel Mux (DMACHMUX)
MPC5606S Microcontroller Reference Manual, Rev. 7
Freescale Semiconductor 457
• 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 (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.
• Use explicit software re-activation.
In this option, the DMA is configured to transfer the data using both minor and major loops, but
the processor is required to re-activate the channel (by writing to the DMA registers) after every
minor loop. For this option, the DMA channel should 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 re-activation. For this option, the DMA channel should be
enabled and pointing to an always-enabled source. Note that the re-activation 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.
13.5 Initialization/application information
13.5.1 Reset
The reset state of each individual bit is shown within the register description section (See Section 13.3.1,
Register descriptions). In summary, after reset, all channels are disabled and must be explicitly enabled
before use.
13.5.2 Enabling and configuring sources
13.5.2.1 Enabling a source with periodic triggering
1. Determine with which DMA channel the source will be associated. Note that only the first four
DMA channels have periodic triggering capability.
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