Ameba-D User Manual
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Fig 9-3 Peripheral-to-Memory DMA transfer on separate AHB layers
9.1.2
Basic Definitions
The following terms are concise definitions of the DMA concepts used throughout this databook:
Source peripheral
– Device on a AHB layer from which the DMAC reads data; the DMAC then stores the data in the channel FIFO. The
source peripheral teams up with a destination peripheral to form a channel. The source peripheral is either an AHB or APB slave. If the
source is an APB slave, it is accessed through the AHB-APB bridge.
Destination peripheral
– Device to which the DMAC writes the stored data from the FIFO (previously read from the source peripheral).
The destination peripheral is either an AHB or APB slave. If the destination is an APB slave, it is accessed through the AHB-APB bridge.
Memory
– Source or destination that is always ready for a DMA transfer and does not require a handshaking interface to interact with
the DMAC. A peripheral should be assigned as memory only if it does not insert more than 16 wait states. If more than 16 wait states are
required, then the peripheral should use a handshaking interface—the default if the peripheral is not programmed to be memory—in
order to signal when the peripheral is ready to accept or supply data. A memory peripheral can also generate SPLIT/RETRY responses.
Channel
– Read/write data path between a source peripheral on one configured AHB layer and a destination peripheral on the same or
different AHB layer that occurs through the channel FIFO. If the source peripheral is not memory, then a source handshaking interface is
assigned to the channel. If the destination peripheral is not memory, then a destination handshaking interface is assigned to the channel.
Source and destination handshaking interfaces can be assigned dynamically by programming the channel registers.
Master interface
– DMAC is a master on the AHB bus, reading data from the source and writing it to the destination over the AHB bus. It
is possible to have up to four master interfaces, which means that up to four independent source and destination channels can operate
simultaneously. Each channel has to arbitrate for the master interface. You need to have more than one master interface if the source
and destination peripherals reside on different AHB layers.
Slave interface
– The AHB interface over which the DMAC is programmed. The slave interface in practice can be on the same layer as any
of the master interfaces, or it can be on a separate layer.
Handshaking interface
– A set of signals or software registers that conform to a protocol and handshake between the DMAC and source
or destination peripheral in order to control transferring a single or burst transaction between them. This interface is used to request,
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