Functional Description
5-50
ADSP-BF537 Blackfin Processor Hardware Reference
Temporary DMA Urgency
Typically, DMA transfers for a given peripheral occur at regular intervals.
Generally, the shorter the interval, the higher the priority that should be
assigned to the peripheral. If the average bandwidth of all the peripherals
is not too large a fraction of the total, then all peripherals’ requests should
be granted as required.
Occasionally, instantaneous DMA traffic might exceed the available band-
width, causing congestion. This may occur if L1 or external memory is
temporarily stalled, perhaps for an SDRAM page swap or a cache line fill.
Congestion might also occur if one or more DMA channels initiates a
flurry of requests, perhaps for descriptor fetches or to fill a FIFO in the
DMA or in the peripheral.
If congestion persists, lower priority DMA peripherals may become
starved for data. Even though the peripheral’s priority is low, if the neces-
sary data transfer does not take place before the end of the peripheral’s
regular interval, system failure may result. To minimize this possibility,
the DMA unit detects peripherals whose need for data has become urgent,
and preferentially grants them service at the highest priority.
A DMA channel’s request for memory service is defined as “urgent” if
both:
• The channel’s FIFO is not ready for a DAB bus transfer (that is, a
transmit FIFO is empty or a receive FIFO is full), and
• The peripheral is asserting its DMA request line.
Descriptor fetches may be urgent, if they are necessary to initiate or con-
tinue a DMA work unit chain for a starving peripheral.
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 ...