ADSP-BF50x Blackfin Processor Hardware Reference
7-17
Direct Memory Access
Note that every descriptor fetch consumes bandwidth from either the
DCB bus or the DEB bus and the external memory interface, so it is best
to keep the size of descriptors as small as possible.
Mixing Flow Modes
The
FLOW
mode of a DMA is not a global setting. If the DMA configura-
tion word is reloaded with a descriptor fetch, the
FLOW
and
NDSIZE
bit
fields can also be altered. A small descriptor might be used to loop back to
the first descriptor if a descriptor array is used in an endless manner. If the
descriptor chain is not endless and the DMA is required to stop after a
certain descriptor has been processed, the last descriptor is typically pro-
cessed in stop mode. That is, its
FLOW
and
NDSIZE
fields are 0, but its
DMAEN
bit is still set.
Functional Description
The following sections provide a functional description of DMA.
DMA Operation Flow
Figure 7-1
and
Figure 7-2
describe the DMA flow.
DMA Startup
This section discusses starting DMA “from scratch.” This is similar to
starting it after it has been paused by the FLOW = 0 mode.
Before initiating DMA for the first time on a given channel, all parameter
registers must be initialized. Be sure to initialize the upper 16 bits of the
DMAx_NEXT_DESC_PTR
(or
DMAx_CURR_DESC_PTR
register in
FLOW
= 4 mode)
and
DMAx_START_ADDR
registers, because they might not otherwise be
accessed, depending upon the flow mode. Also note that the
Summary of Contents for EZ-KIT Lite ADSP-BF506F
Page 50: ...Contents l ADSP BF50x Blackfin Processor Hardware Reference ...
Page 92: ...Development Tools 1 30 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 110: ...Interface Overview 3 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 236: ...Internal Flash Memory Control Registers 6 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 650: ...Programming Examples 15 56 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 804: ...Programming Examples 17 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1194: ...Programming Examples 24 90 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1256: ...ACM Registers A 50 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1264: ...Boundary Scan Architecture B 8 ADSP BF50x Blackfin Processor Hardware Reference ...