• Cycle-steal mode (DCRn[CS] = 1)—Only one complete transfer from source to
destination occurs for each request. If DCRn[ERQ] is set, the request is peripheral
initiated. A software-initiated request is enabled by setting DCRn[START].
• Continuous mode (DCRn[CS] = 0)—After a software-initiated or peripheral request,
the DMA continuously transfers data until BCRn reaches 0. The DMA performs the
specified number of transfers, then retires the channel.
In either mode, the crossbar switch performs independent arbitration on each slave port
after each transaction.
21.4.2 Channel initialization and startup
Before a data transfer starts, the channel's transfer control descriptor must be initialized
with information describing configuration, request-generation method, and pointers to the
data to be moved.
21.4.2.1 Channel prioritization
The four DMA channels are prioritized based on number, with channel 0 having highest
priority and channel 3 having the lowest, that is, channel 0 > channel 1 > channel 2 >
channel 3.
Simultaneous peripheral requests activate the channels based on this priority order. Once
activated, a channel runs to completion as defined by DCRn[CS] and BCRn.
21.4.2.2 Programming the DMA Controller Module
CAUTION
During a channel's execution, writes to programming model
registers can corrupt the data transfer. The DMA module itself
does not have a mechanism to prevent writes to registers during
a channel's execution.
General guidelines for programming the DMA are:
• TCDn is initialized.
Functional Description
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