PXD10RM Datasheet, PDF (459/1332 Pages) Freescale Semiconductor, Inc – PXD10 Microcontroller

• 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, a "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 (i.e.-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 a "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
Enabling a source with periodic triggering
1. Determine with which DMA channel the source will be associated. Note that only the first 4 DMA
channels have periodic triggering capability.
2. Clear the ENBL and TRIG bits of the DMA channel
3. Ensure that the DMA channel is properly configured in the DMA. The DMA channel may be
enabled at this point
Freescale Semiconductor
PXD10 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
13-9