
Functional Description
5-44
ADSP-BF59x Blackfin Processor Hardware Reference
DMA in
SCLK
s (which is typically seven for internal transfers and six for
external transfers).
Memory DMA Timing Details
When the destination
DMAx_CONFIG
register is written, MDMA operation
starts after a latency of three
SCLK
cycles.
If either MDMA channel has been selected to use descriptors, the descrip-
tors are fetched from memory. The destination channel descriptors are
fetched first. Then the source MDMA channel begins fetching data from
the source buffer, after a latency of four
SCLK
cycles after the last descrip-
tor word is returned from memory. Due to memory pipelining, this is
typically eight
SCLK
cycles after the fetch of the last descriptor word. The
resulting data is deposited in the MDMA channel’s 8-location FIFO.
After a latency of two
SCLK
cycles, the destination MDMA channel begins
writing data to the destination memory buffer.
Static Channel Prioritization
DMA channels are ordinarily granted service strictly according to their
priority. The priority of a channel is simply its channel number, where
lower priority numbers are granted first. Thus, peripherals with high data
rates or low latency requirements should be assigned to lower numbered
(higher priority) channels using the
PMAP
field in the
DMAx_PERIPHERAL_MAP
registers. The memory DMA streams are always
lower static priority than the peripherals, but as they request service con-
tinuously, they ensure that any time slots unused by peripheral DMA are
applied to MDMA transfers.
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
Содержание ADSP-BF59x Blackfin
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