
ADSP-BF59x Blackfin Processor Hardware Reference
5-55
Direct Memory Access
DMAx_Y_COUNT
shows a value of 3, then the software should assume
that sub-buffer 3 is being transferred, but some portion of sub-buf-
fer 2 may not yet be received. The software could, however, safely
proceed with processing sub-buffers 1 or 0.
• 1-D unsynchronized FIFO—if a system’s design guarantees that
the processing of a peripheral’s data and the DMA rate of the data
will remain correlated in the steady state, but that short-term
latency variations must be tolerated, it may be appropriate to build
a simple FIFO. Here, the DMA channel may be programmed using
1-D autobuffer mode addressing without any interrupts or polling.
Descriptor Structures
DMA descriptors may be used to transfer data to or from memory data
structures that are not simple 1-D or 2-D arrays. For example, if a packet
of data is to be transmitted from several different locations in memory (a
header from one location, a payload from a list of several blocks of mem-
ory managed by a memory pool allocator, and a small trailer containing a
checksum), a separate DMA descriptor can be prepared for each memory
area, and the descriptors can be grouped in either an array or list by select-
ing the appropriate
FLOW
setting in
DMAx_CONFIG
.
The software can synchronize with the progress of the structure’s transfer
by selecting interrupt notification for one or more of the descriptors. For
example, the software might select interrupt notification for the header’s
descriptor and for the trailer’s descriptor, but not for the payload blocks’
descriptors.
It is important to remember the meaning of the various fields in the
DMAx_CONFIG
descriptor elements when building a list or array of DMA
descriptors. In particular:
• The lower byte of
DMAx_CONFIG
specifies the DMA transfer to be
performed by the
current
descriptor (for example 2-D inter-
rupt-enable mode)
Содержание ADSP-BF59x Blackfin
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Страница 74: ...Processor Specific MMRs 2 10 ADSP BF59x Blackfin Processor Hardware Reference...
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Страница 244: ...Programming Examples 6 40 ADSP BF59x Blackfin Processor Hardware Reference...
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Страница 738: ...Boundary Scan Architecture B 8 ADSP BF59x Blackfin Processor Hardware Reference...