
ADSP-BF59x Blackfin Processor Hardware Reference
5-47
Direct Memory Access
If this field is set to 0, then MDMA is scheduled by fixed priority.
MDMA stream 0 takes precedence over MDMA stream 1 whenever
stream 0 is ready to perform transfers. Since an MDMA stream is typically
capable of transferring data on every available cycle, this could cause
MDMA stream 1 traffic to be delayed for an indefinite time until any and
all MDMA stream 0 operations are completed. This scheme could be
appropriate in systems where low duration but latency-sensitive data buf-
fers need to be moved immediately, interrupting long duration, low
priority background transfers.
If the
MDMA_ROUND_ROBIN_PERIOD
field is set to some nonzero value in the
range 1
≤
P
≤
31, then a round-robin scheduling method is used. The two
MDMA streams are granted bus access in alternation in bursts of up to P
data transfers. This could be used in systems where two transfer processes
need to coexist, each with a guaranteed fraction of the available band-
width. For example, one stream might be programmed for
internal-to-external moves while the other is programmed for exter-
nal-to-internal moves, and each would be allocated approximately equal
data bandwidth.
In round-robin operation, the MDMA stream selection at any time is
either “free” or “locked.” Initially, the selection is free. On any free cycle
available to MDMA (when no peripheral DMA accesses take precedence),
if either or both MDMA streams request access, the higher precedence
stream will be granted (stream 0 in case of conflict), and that stream’s
selection is then “locked.” The
MDMA_ROUND_ROBIN_COUNT
counter field in
the
DMA_TC_CNT
register is loaded with the period P from
MDMA_ROUND_ROBIN_PERIOD
, and MDMA transfers begin. The counter is
decremented on every data transfer (as each data word is written to mem-
ory). After the transfer corresponding to a count of one, the MDMA
stream selection is passed automatically to the other stream with zero over-
head, and the
MDMA_ROUND_ROBIN_COUNT
counter is reloaded with the
period value P from
MDMA_ROUND_ROBIN_PERIOD
. In this cycle, if the other
MDMA stream is ready to perform a transfer, the stream selection is
locked on the new MDMA stream. If the other MDMA stream is not
Summary of Contents for ADSP-BF59x Blackfin
Page 64: ...Development Tools 1 22 ADSP BF59x Blackfin Processor Hardware Reference...
Page 74: ...Processor Specific MMRs 2 10 ADSP BF59x Blackfin Processor Hardware Reference...
Page 244: ...Programming Examples 6 40 ADSP BF59x Blackfin Processor Hardware Reference...
Page 700: ...Programming Examples 16 78 ADSP BF59x Blackfin Processor Hardware Reference...
Page 738: ...Boundary Scan Architecture B 8 ADSP BF59x Blackfin Processor Hardware Reference...