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ADSP-BF537 Blackfin Processor Hardware Reference
5-67
Direct Memory Access
If all
DMACFG
fields in a descriptor chain have the
FLOW
and
NDSIZE
fields set
to zero, the individual DMA sequences do not start until triggered by soft-
ware. This is useful when the DMAs need to be synchronized with other
events in the system, and it is typically performed by interrupt service rou-
tines. A single MMR write is required to trigger the next DMA sequence.
Especially when applied to MDMA channels, such scenarios play an
important role. Usually, the timing of MDMAs cannot be controlled (See
“Handshaked Memory DMA Operation” on page 5-40
). By halting
descriptor chains or rings this way, the whole DMA transaction can be
broken into pieces that are individually triggered by software.
L
Source and destination channels of a MDMA may differ in descrip-
tor structure. However, the total work count must match when the
DMA stops. Whenever a MDMA is stopped, destination and
source channels should both provide the same
FLOW
=
0
mode after
exactly the same number of words. Accordingly, both channels
need to be started afterward.
Software triggered descriptor fetches are illustrated in
. MDMA channels can be paused by software at any time by
writing a 0 to the
DRQ
bit field in the
HMDMAx_CONTROL
register. This simply
disables the self-generated DMA requests, regardless whether HMDMA is
enabled or not.
DMA Registers
DMA registers fall into three categories:
• DMA channel registers
• Handshaked MDMA registers
• Global DMA traffic control registers
Содержание Blackfin ADSP-BF537
Страница 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...