ADSP-BF537 Blackfin Processor Hardware Reference
5-29
Direct Memory Access
however, and not yet at the peripheral, so the DMA interrupt should not
be used as the sole means of synchronizing the shutdown or reconfigura-
tion of the peripheral following a transmission.
L
If
SYNC = 0
(continuous transition) on a transmit (memory read)
descriptor, the next descriptor is required to have the same data
word size, read/write direction, and source memory (internal vs.
external) as the current descriptor.
If
SYNC = 0
selects continuous transition on a work unit in
FLOW = STOP
mode with interrupt enabled, the interrupt service routine may already
run while the final data is still draining from the FIFO to the peripheral.
This is indicated by the
DMA_RUN
bit in the
DMAx_IRQ_STATUS
register; if it
is 1, the FIFO is not empty yet. Do not start a new work unit with differ-
ent word size or direction while
DMA_RUN = 1
. Further, if the channel is
disabled (by writing
DMAEN = 0
), the data in the FIFO is lost.
If
SYNC = 1
, a synchronized transition is selected, in which the DMA FIFO
is first drained to the destination memory or peripheral before any inter-
rupt is signalled and before any subsequent descriptor or data is fetched.
This incurs greater latency, but provides direct synchronization between
the DMA interrupt and the state of the data at the peripheral.
For example, if
SYNC = 1
and
DI_EN = 1
on the last descriptor in a work
unit, the interrupt occurs when the final data has been transferred to the
peripheral, allowing the service routine to properly switch to non-DMA
transmit operation. When the interrupt service routine is invoked, the
DMA_DONE
bit is set and the
DMA_RUN
bit is cleared.
A synchronized transition also allows greater flexibility in the format of
the DMA descriptor chain. If
SYNC = 1
, the next descriptor may have any
word size or read/write direction supported by the peripheral and may
come from either memory space (internal vs. external). This can be useful
in managing MDMA work unit queues, since it is no longer necessary to
interrupt the queue between dissimilar work units.
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 ...