Direct Memory Access Controller (DMAC)
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acknowledge, and control a DMAC transaction. A channel can receive a request through one of three types of handshaking interface:
hardware, software, or peripheral interrupt.
Hardware handshaking interface
– Uses hardware signals to control transferring a single or burst transaction between the DMAC
and the source or destination peripheral.
Peripheral interrupt handshaking interface
– Simple use of the hardware handshaking interface. In this mode, the interrupt line
from the peripheral is tied to the dma_req input of the hardware handshaking interface; other interface signals are ignored.
Flow controller
– Device (either the DMAC, or source/destination peripheral) that determines the length of a DMA block transfer and
terminates it.
If you know the length of a block before enabling the channel, then you should program the DMAC as the flow controller.
If the length of a block is not known prior to enabling the channel, the source or destination peripheral needs to terminate a block
transfer. In this mode, the peripheral is the flow controller.
Flow control mode
(CFGx.FCMODE) – Special mode that only applies when the destination peripheral is the flow controller. It controls
the data pre-fetching from the source peripheral.
Transfer hierarchy
–Fig 9-4 illustrates the hierarchy between DMA transfers, block transfers, transactions (single or burst), and AHB
transfers (single or burst) for non-memory peripherals. Fig 9-5 shows the transfer hierarchy for memory.
Note
: For memory peripherals, there is no DMA Transaction Level.
Fig 9-4 DMA Transfer Hierarchy for Non-Memory Peripherals
Fig 9-5 DMA transfer hierarchy for memory
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2019-05-15 10:08:03