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AT32F435/437
Series Reference Manual
2022.11.11
Page 677
Rev 2.03
6.
Enable DMA transfer through the SEN bit in the DMA_SxCTRL register
29.3.2 Channel selection and synchronizer
The clocks between a peripheral and DMA may be asynchronous. The user can choose whether the
synchronizer of the dma_chx_req is needed.
Figure 29-2 shows the block diagram of channel selection and synchronizer.
Figure 29-2 Channel select and synchronizer
dma_req_ch8
dma_req_ch7
dma_req_ch6
dma_req_ch5
dma_req_ch4
dma_req_ch3
dma_req_ch2
dma_req_ch1
dma_req
dma_req_async
CHSEL[2:0]
hclk
SYNC_EN
29.3.3 Handshake mechanism
In P2M and M2P mode, the peripherals need to send a request signal to the DMA controller. The DMA
channel will send the peripheral transfer request (single or burst) until the signal is acknowledged. After
the completion of peripheral transmission, the DMA controller sends an acknowledge signal to the
peripheral. The peripheral then releases its request as soon as it receives the acknowledge signal. At
the same time, the DMA controller releases the acknowledge signal as well.
In non-incrementing mode (PINCM = 0), burst transfers 4, 8 or 16 beats are translated into 4, 8 or 16
single transfers. These data will be transferred by the main peripheral controller in a
request/acknowledge group.
In peripheral flow control mode (PFCTRL = 1), only a single transfer is present in a request/ acknowledge
group.
29.3.4 Arbiter
When several channels are enabled simultaneously, the arbiter will restart arbitration after full data
transfer by the master controller. The channel with very high priority waits until the channel of the master
controller has completed data transfers before taking control of it. The master controller will re-arbitrate
to serve other channels as long as the channel completes a single transfer based on the master
controller priority.
Figure 29-3 shows the behavior between DMA request/acknowledge and arbiter. Since there is only one
single or burst transfer in a request/acknowledge group, it works in the same way as a re-arbitration
mechanism. Thus the main peripheral controller will re-arbitrate to serve other channels each time a
channel completes a single or burst transfer according to the priority defined by the main controller.