ADSP-BF537 Blackfin Processor Hardware Reference
5-31
Direct Memory Access
If a descriptor chain begins with a
SYNC
bit of 1, there is no restriction on
DMA word size of the new chain in comparison to the previous chain.
L
The DMA word size must not change between one descriptor and
the next in any DMA receive (memory write) channel within a sin-
gle descriptor chain, regardless of the
SYNC
bit setting. In other
words, if a descriptor has
WNR = 1
and
FLOW = 4
,
6
, or
7
, then the
next descriptor must have the same word size. For any DMA
receive (memory write) channel, there is no restriction on changes
of memory space (internal vs. external) between descriptors or
descriptor chains. DMA transmit (memory read) channels may
have such restrictions (see
“DMA Transmit and MDMA Source”
).
Stopping DMA Transfers
In
FLOW = 0
mode, DMA stops automatically after the work unit is
complete.
If a list or array of descriptors is used to control DMA, and if every
descriptor contains a
DMACFG
element, then the final
DMACFG
element
should have a
FLOW = 0
setting to gracefully stop the channel.
In autobuffer (
FLOW = 1
) mode, or if a list or array of descriptors without
DMACFG
elements is used, then the DMA transfer process must be termi-
nated by an MMR write to the
DMAx_CONFIG
register with a value whose
DMAEN
bit is 0. A write of 0 to the entire register will always terminate
DMA gracefully (without DMA abort).
a
If a channel has been stopped abruptly by writing
DMAx_CONFIG
to 0
(or any value with
DMAEN = 0
), the user must ensure that any mem-
ory read or write accesses in the pipelines have completed before
enabling the channel again. If the channel is enabled again before
an “orphan” access from a previous work unit completes, the state
of the DMA interrupt and FIFO is unspecified. This can generally
be handled by ensuring that the core allocates several idle cycles in
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...