Information

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.
20.5 Initialization/application information
This section provides instructions for initializing the DMA channel MUX.
20.5.1 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.
20.5.2 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] 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.
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] bits are set.
To configure source #5 transmit for use with DMA channel 2, with periodic triggering
capability:
1. Write 0x00 to CHCFG2 (base address + 0x02).
2. Configure channel 2 in the DMA, including enabling the channel.
3. Configure a timer for the desired trigger interval.
4. Write 0xC5 to CHCFG2 (base address + 0x02).
The following code example illustrates steps 1 and 4 above:
In File registers.h:
#define DMAMUX_BASE_ADDR 0xFC084000/* Example only ! */
/* Following example assumes char is 8-bits */
volatile unsigned char *CHCONFIG0 = (volatile unsigned char *) (DMAMUX_BASE_ADDR+0x0000);
volatile unsigned char *CHCONFIG1 = (volatile unsigned char *) (DMAMUX_BASE_ADDR+0x0001);
volatile unsigned char *CHCONFIG2 = (volatile unsigned char *) (DMAMUX_BASE_ADDR+0x0002);
volatile unsigned char *CHCONFIG3 = (volatile unsigned char *) (DMAMUX_BASE_ADDR+0x0003);
Chapter 20 Direct Memory Access Multiplexer (DMAMUX)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 329