Functional Description
5-24
ADSP-BF537 Blackfin Processor Hardware Reference
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 elements, overwrit-
ing 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
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 ...