Direct memory access controller (DMA) RM0440
406/2126 RM0440 Rev 4
peripheral or memory, and is programmed in the DMA_CPARx or DMA_CMARx
register.
– a single data write (byte, half-word or word) to the peripheral data register or a
location in the memory, addressed through an internal current peripheral/memory
address register.
The start address used for the first transfer is the base address of the peripheral or
memory, and is programmed in the DMA_CPARx or DMA_CMARx register.
• post-decrementing of the programmed DMA_CNDTRx register
This register contains the remaining number of data items to transfer (number of AHB
‘read followed by write’ transfers).
This sequence is repeated until DMA_CNDTRx is null.
Note: The AHB master bus source/destination address must be aligned with the programmed size
of the transferred single data to the source/destination.
12.4.4 DMA arbitration
The DMA arbiter manages the priority between the different channels.
When an active channel x is granted by the arbiter (hardware requested or software
triggered), a single DMA transfer is issued (such as a AHB ‘read followed by write’ transfer
of a single data). Then, the arbiter considers again the set of active channels and selects the
one with the highest priority.
The priorities are managed in two stages:
• software: priority of each channel is configured in the DMA_CCRx register, to one of
the four different levels:
– very high
–high
–medium
–low
• hardware: if two requests have the same software priority level, the channel with the
lowest index gets priority. For example, channel 2 gets priority over channel 4.
When a channel x is programmed for a block transfer in memory-to-memory mode,
re arbitration is considered between each single DMA transfer of this channel x. Whenever
there is another concurrent active requested channel, the DMA arbiter automatically
alternates and grants the other highest-priority requested channel, which may be of lower
priority than the memory-to-memory channel.
12.4.5 DMA channels
Each channel may handle a DMA transfer between a peripheral register located at a fixed
address, and a memory address. The amount of data items to transfer is programmable.
The register that contains the amount of data items to transfer is decremented after each
transfer.
A DMA channel is programmed at block transfer level.
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