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ADSP-BF537 Blackfin Processor Hardware Reference
5-27
Direct Memory Access
• If
FLOW
=
4, 6, or 7
(descriptor array, descriptor list small, or
descriptor list large, respectively) the DMA controller clears the
DFETCH
bit in the
DMAx_IRQ_STATUS
register.
• If
FLOW
= any value but 0 (Stop), the DMA controller begins the
next work unit, contending with other channels for priority on the
memory buses. On the first memory transfer of the new work unit,
the DMA controller updates the current registers from the start
registers:
DMAx_CURR_ADDR
loaded from
DMAx_START_ADDR
DMAx_CURR_X_COUNT
loaded from
DMAx_X_COUNT
DMAx_CURR_Y_COUNT
loaded from
DMAx_Y_COUNT
The
DFETCH
bit in
DMAx_IRQ_STATUS
is then cleared, after which the
DMA transfer begins again, as shown in
.
Work Unit Transitions
Transitions from one work unit to the next are controlled by the
SYNC
bit
in the
DMAx_CONFIG
register of the work units. In general, continuous tran-
sitions have lower latency at the cost of restrictions on changes of data
format or addressed memory space in the two work units. These latency
gains and data restrictions arise from the way the DMA FIFO pipeline is
handled while the next descriptor is fetched. In continuous transitions
(
SYNC
=
0
), the DMA FIFO pipeline continues to transfer data to and from
the peripheral or destination memory during the descriptor fetch and/or
when the DMA channel is paused between descriptor chains.
Synchronized transitions (
SYNC
=
1
), on the other hand, provide better
real-time synchronization of interrupts with peripheral state and greater
flexibility in the data formats and memory spaces of the two work units, at
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 ...