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ADSP-BF537 Blackfin Processor Hardware Reference
5-51
Direct Memory Access
DMA requests from an MDMA channel become urgent when handshaked
operation is enabled and the DMARx edge count exceeds the value stored
in the
HMDMAx_ECURGENT
register. If handshaked operation is disabled, soft-
ware can control urgency of requests directly by altering the
DRQ
bit field
in the
HMDMAx_CONTROL
register.
When one or more DMA channels express an urgent memory request, two
events occur:
• All non-urgent memory requests are decreased in priority by 32,
guaranteeing that only an urgent request will be granted. The
urgent requests compete with each other, if there is more than one,
and directional preference among urgent requests is observed.
• The resulting memory transfer is marked for expedited processing
in the targeted memory system (L1 or external), and so are all prior
incomplete memory transfers ahead of it in that memory system.
This may cause a series of external memory core accesses to be
delayed for a few cycles so that a peripheral’s urgent request may be
accommodated.
The preferential handling of urgent DMA transfers is completely auto-
matic. No user controls are required for this function to operate.
Memory DMA Priority and Scheduling
All MDMA operations have lower precedence than any peripheral DMA
operations. MDMA thus makes effective use of any memory bandwidth
unused by peripheral DMA traffic.
By default, when more than one MDMA stream is enabled and ready,
only the highest priority MDMA stream is granted. If it is desirable for the
MDMA streams to share the available bandwidth, however, the
MDMA_
ROUND_ROBIN_PERIOD
may be programmed to select each stream in turn for
a fixed number of transfers.
Содержание Blackfin ADSP-BF537
Страница 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...