23.4.2 Channel Initialization and Startup
Before a data transfer starts, the channel's transfer control descriptor must be initialized
with information describing configuration, request-generation method, and pointers to the
data to be moved.
23.4.2.1 Channel Prioritization
The four DMA channels are prioritized based on number, with channel 0 having highest
priority and channel 3 having the lowest, that is, channel 0 > channel 1 > channel 2 >
channel 3.
Simultaneous peripheral requests activate the channels based on this priority order. Once
activated, a channel runs to completion as defined by DCRn[CS] and BCRn.
23.4.2.2 Programming the DMA Controller Module
CAUTION
During a channel's execution, writes to programming model
registers can corrupt the data transfer. The DMA module itself
does not have a mechanism to prevent writes to registers during
a channel's execution.
General guidelines for programming the DMA are:
• TCDn is initialized.
• SARn is loaded with the source (read) address. If the transfer is from a
peripheral device to memory or to another peripheral, the source address is the
location of the peripheral data register. If the transfer is from memory to a
peripheral device or to memory, the source address is the starting address of the
data block. This can be any appropriately aligned address.
• DARn is initialized with the destination (write) address. If the transfer is from a
peripheral device to memory, or from memory to memory, DARn is loaded with
the starting address of the data block to be written. If the transfer is from
memory to a peripheral device, or from a peripheral device to a peripheral
device, DARn is loaded with the address of the peripheral data register. This
address can be any appropriately aligned address.
Functional Description
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
362 Freescale Semiconductor, Inc.
To Next Page
Loading...
