
ADSP-BF59x Blackfin Processor Hardware Reference
5-21
Direct Memory Access
If
DMACFG
is not part of the descriptor, the previous
DMAx_CONFIG
settings
(as written by MMR access at startup) control the work unit operation. If
DMACFG
is part of the descriptor, then the
DMAx_CONFIG
value programmed
by the MMR access controls only the loading of the first descriptor from
memory. The subsequent DMA work operation is controlled by the low
byte of the descriptor’s
DMACFG
and by the parameter registers loaded from
the descriptor. The bits
DI_EN
,
DI_SEL
,
DMA2D
,
WDSIZE
, and
WNR
in the value
programmed by the MMR access are disregarded.
The
DMA_RUN
and
DFETCH
status bits in the
DMAx_IRQ_STATUS
register indi-
cate the state of the DMA channel. After a write to
DMAx_CONFIG
, the
DMA_RUN
and
DFETCH
bits can be automatically set to 1. No data interrupts
are signaled as a result of loading the first descriptor from memory.
After the above steps, DMA data transfer operation begins. The DMA
channel immediately attempts to fill its FIFO, subject to channel prior-
ity—a memory write (RX) DMA channel begins accepting data from its
peripheral, and a memory read (TX) DMA channel begins memory reads,
provided the channel wins the grant for bus access.
When the DMA channel performs its first data memory access, its address
and count computations take their input operands from the start registers
(
DMAx_START_ADDR
,
DMAx_X_COUNT
,
DMAx_Y_COUNT
), and write results back
to the current registers (
DMAx_CURR_ADDR
,
DMAx_CURR_X_COUNT
,
DMAx_CURR_Y_COUNT
). Note also that the current registers are not valid
until the first memory access is performed, which may be some time after
the channel is started by the write to the
DMA_CONFIG
register. The current
registers are loaded automatically from the appropriate descriptor ele-
ments, overwriting their previous contents, as follows.
•
DMAx_START_ADDR
is copied to
DMAx_CURR_ADDR
•
DMAx_X_COUNT
is copied to
DMAx_CURR_X_COUNT
•
DMAx_Y_COUNT
is copied to
DMAx_CURR_Y_COUNT
Содержание ADSP-BF59x Blackfin
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Страница 74: ...Processor Specific MMRs 2 10 ADSP BF59x Blackfin Processor Hardware Reference...
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Страница 244: ...Programming Examples 6 40 ADSP BF59x Blackfin Processor Hardware Reference...
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Страница 738: ...Boundary Scan Architecture B 8 ADSP BF59x Blackfin Processor Hardware Reference...