ST STM32F301 6 Series Reference Manual page 157

RM0366
10.4.2 DMA transfers
The software configures the DMA controller at channel level, to perform a block transfer,
composed of a sequence of AHB bus transfers.
A DMA block transfer may be requested from a peripheral, or triggered by the software in
case of memory-to-memory transfer.
After an event, the following steps of a single DMA transfer occur:
1. The peripheral sends a single DMA request signal to the DMA controller.
2. The DMA controller serves the request, depending on the priority of the channel
associated to this peripheral request.
3. As soon as the DMA controller grants the peripheral, an acknowledge is sent to the
peripheral by the DMA controller.
4. The peripheral releases its request as soon as it gets the acknowledge from the DMA
controller.
5. Once the request is deasserted by the peripheral, the DMA controller releases the
acknowledge.
The peripheral may order a further single request and initiate another single DMA transfer.
The request/acknowledge protocol is used when a peripheral is either the source or the
destination of the transfer. For example, in case of memory-to-peripheral transfer, the
peripheral initiates the transfer by driving its single request signal to the DMA controller. The
DMA controller reads then a single data in the memory and writes this data to the peripheral.
For a given channel x, a DMA block transfer consists of a repeated sequence of:
•
a single DMA transfer, encapsulating two AHB transfers of a single data, over the DMA
AHB bus master:
–
–
•
postdecrementing 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.
a single data read (byte, half-word, or word) from 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 single transfer is the base address of the
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.
Direct memory access controller (DMA)
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