ST STM32L4+ Series Reference Manual page 382

Direct memory access controller (DMA)
automatically reloaded with the initial value programmed during the channel configuration
phase, and the DMA requests continue to be served.
In order to stop a circular transfer, the software needs to stop the peripheral from generating
DMA requests (such as quit the ADC scan mode), before disabling the DMA channel.
The software must explicitly program the DMA_CNDTRx value before starting/enabling a
transfer, and after having stopped a circular transfer.
Memory-to-memory mode
The DMA channels may operate without being triggered by a request from a peripheral. This
mode is called memory-to-memory mode, and is initiated by software.
If the MEM2MEM bit in the DMA_CCRx register is set, the channel, if enabled, initiates
transfers. The transfer stops once the DMA_CNDTRx register reaches zero.
Note: The memory-to-memory mode must not be used in circular mode. Before enabling a
channel in memory-to-memory mode (MEM2MEM = 1), the software must clear the CIRC
bit of the DMA_CCRx register.
Peripheral-to-peripheral mode
Any DMA channel can operate in peripheral-to-peripheral mode:
•
when the hardware request from a peripheral is selected to trigger the DMA channel
This peripheral is the DMA initiator and paces the data transfer from/to this peripheral
to/from a register belonging to another memory-mapped peripheral (this one being not
configured in DMA mode).
•
when no peripheral request is selected and connected to the DMA channel
The software configures a register-to-register transfer by setting the MEM2MEM bit of
the DMA_CCRx register.
Programming transfer direction, assigning source/destination
The value of the DIR bit of the DMA_CCRx register sets the direction of the transfer, and
consequently, it identifies the source and the destination, regardless the source/destination
type (peripheral or memory):
•
DIR = 1 defines typically a memory-to-peripheral transfer. More generally, if DIR = 1:
–
–
•
DIR = 0 defines typically a peripheral-to-memory transfer. More generally, if DIR = 0:
–
–
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The source attributes are defined by the DMA_MARx register, the MSIZE[1:0]
field and MINC bit of the DMA_CCRx register.
Regardless of their usual naming, these 'memory' register, field and bit are used to
define the source peripheral in peripheral-to-peripheral mode.
The destination attributes are defined by the DMA_PARx register, the PSIZE[1:0]
field and PINC bit of the DMA_CCRx register.
Regardless of their usual naming, these 'peripheral' register, field and bit are used
to define the destination memory in memory-to-memory mode.
The source attributes are defined by the DMA_PARx register, the PSIZE[1:0] field
and PINC bit of the DMA_CCRx register.
Regardless of their usual naming, these 'peripheral' register, field and bit are used
to define the source memory in memory-to-memory mode
The destination attributes are defined by the DMA_MARx register, the
MSIZE[1:0] field and MINC bit of the DMA_CCRx register.
RM0432 Rev 6
RM0432