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.
21.5 Initialization/application information
This section provides instructions for initializing the DMA channel MUX.
21.5.1 Reset
The reset state of each individual bit is shown in
Memory map/register definition
. In
summary, after reset, all channels are disabled and must be explicitly enabled before use.
21.5.2 Enabling and configuring sources
To enable 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 CHCFG[ENBL] and CHCFG[TRIG] fields 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.
4. Configure the corresponding timer.
5. Select the source to be routed to the DMA channel. Write to the corresponding
CHCFG register, ensuring that the CHCFG[ENBL] and CHCFG[TRIG] fields are
set.
NOTE
The following is an example. See the chip configuration details
for the number of this device's DMA channels that have
triggering capability.
To configure source #5 transmit for use with DMA channel 1, with periodic triggering
capability:
1. Write 0x00 to CHCFG1 (base a 0x01).
Chapter 21 Direct Memory Access Multiplexer (DMAMUX)
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
Freescale Semiconductor, Inc.
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