• Continuous-mode or cycle-steal transfers from software or peripheral initiation
• Automatic hardware acknowledge/done indicator from each channel
• Independent source and destination address registers
• Optional modulo addressing and automatic updates of source and destination
addresses
• Independent transfer sizes for source and destination
• Optional auto-alignment feature for source or destination accesses
• Optional automatic single or double channel linking
• Programming model accessed via 32-bit slave peripheral bus
• Channel arbitration on transfer boundaries using fixed priority scheme
23.2 DMA Transfer Overview
The DMA module can move data within system memory (including memory and
peripheral devices) with minimal processor intervention, greatly improving overall
system performance. The DMA module consists of four independent, functionally
equivalent channels, so references to DMA in this chapter apply to any of the channels. It
is not possible to address all four channels at once.
As soon as a channel has been initialized, it may be started by setting DCRn[START] or
a properly-selected peripheral DMA request, depending on the status of DCRn[ERQ].
The DMA controller supports dual-address transfers using its bus master connection to
the system bus. The DMA channels support transfers up to 32 data bits in size and have
the same memory map addressibility as the processor.
• Dual-address transfers—A dual-address transfer consists of a read followed by a
write and is initiated by a request using the DCRn[START] bit or by a peripheral
DMA request. The read data is temporarily held in the DMA channel hardware until
the write operation. Two types of single transfers occur: a read from a source address
followed by a write to a destination address. See the following figure.
Chapter 23 DMA Controller Module
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
Freescale Semiconductor, Inc. 351
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