Functional Description
7-50
ADSP-BF50x Blackfin Processor Hardware Reference
mechanism controlled by the
DMA_TC_PER
and
DMA_TC_CNT
registers. This
mechanism performs the optimization without real-time processor inter-
vention and without the need to program transfer bursts into the DMA
work unit streams. Traffic can be independently controlled for each of the
three buses (DAB, DCB, and DEB) with simple counters. In addition,
alternation of transfers among MDMA streams can be controlled with the
MDMA_ROUND_ROBIN_COUNT
field of the
DMA_TC_CNT
register. See
“Memory
DMA Priority and Scheduling” on page 7-47
.
Using the traffic control features, the DMA system preferentially grants
data transfers on the DAB or memory buses which are going in the same
read/write direction as the previous transfer, until either the traffic control
counter times out or traffic stops or changes direction on its own. When
the traffic counter reaches zero, the preference is changed to the opposite
flow direction. These directional preferences work as if the priority of the
opposite direction channels were decreased by 16.
For example, if channels 3 and 5 were requesting DAB access, but lower
priority channel 5 is going with traffic and higher priority channel 3 is
going against traffic, then channel 3’s effective priority becomes 19, and
channel 5 would be granted instead. If, on the next cycle, only channels 3
and 6 were requesting DAB transfers, and these transfer requests were
both against traffic, then their effective priorities would become 19 and
22, respectively. One of the channels (channel 3) is granted, even though
its direction is opposite to the current flow. No bus cycles are wasted,
other than any necessary delay required for the bus turnaround.
This type of traffic control represents a trade-off of latency to improve uti-
lization (efficiency). Higher traffic timeouts might increase the length of
time each request waits for its grant, but it often dramatically improves the
maximum attainable bandwidth in congested systems, often to above
90%.
To disable preferential DMA prioritization, program the
DMA_TC_PER
reg-
ister to 0x0000.
Summary of Contents for EZ-KIT Lite ADSP-BF506F
Page 50: ...Contents l ADSP BF50x Blackfin Processor Hardware Reference ...
Page 92: ...Development Tools 1 30 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 110: ...Interface Overview 3 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 236: ...Internal Flash Memory Control Registers 6 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 650: ...Programming Examples 15 56 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 804: ...Programming Examples 17 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1194: ...Programming Examples 24 90 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1256: ...ACM Registers A 50 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1264: ...Boundary Scan Architecture B 8 ADSP BF50x Blackfin Processor Hardware Reference ...