RM0401 Rev 3 165/771
RM0401 Direct memory access controller (DMA)
197
Figure 23. System implementation of the two DMA controllers
1. The DMA1 controller AHB peripheral port is not connected to the bus matrix like in the case of the DMA2 controller, thus
only DMA2 streams are able to perform memory-to-memory transfers.
8.3.3 DMA transactions
A DMA transaction consists of a sequence of a given number of data transfers. The number
of data items to be transferred and their width (8-bit, 16-bit or 32-bit) are software-
programmable.
Each DMA transfer consists of three operations:
• a loading from the peripheral data register or a location in memory, addressed through
the DMA_SxPAR or DMA_SxM0AR register
• a storage of the data loaded to the peripheral data register or a location in memory
addressed through the DMA_SxPAR or DMA_SxM0AR register
• a post-decrement of the DMA_SxNDTR register, containing the number of transactions
that still have to be performed
After an event, the peripheral sends a request signal to the DMA controller. The DMA
controller serves the request depending on the channel priorities. As soon as the DMA
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