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
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 ...