Operating Modes
2-44 ADSP-214xx SHARC Processor Hardware Reference
External port/SPORT channel arbitration can be set to use either a fixed
or rotating algorithm by setting the
EPBR bits in the EPCTL register as
follows.
• (00) = Priority order from highest to lowest is SPORT, external
port DMA, core.
• (01) = Priority order from highest to lowest is external port DMA,
SPORT, core.
• (10) = Highest priority is core. SPORT and external port DMA are
in rotating priority.
Rotating DMA Channel Arbitration
DMA channel arbitration is the method that the arbiter uses to determine
how groups rotate priority with other channels. The default DMA channel
priority is fixed prioritization by DMA channel group.
Rotating Priority by Group
In the rotating priority scheme, the default priorities at reset are the same
as that of the fixed priority. However, the peripheral priority is deter-
mined by group, not individually by DMA channel. Peripheral groups are
shown in Table 2-28.
Initially, group A has the highest priority and group I the lowest. As one
group completes its DMA operation, it is assigned the lowest priority
(moves to the back of the line) and the next group is given the highest
priority.
When none of the peripherals request bus access, the highest priority
peripheral, for example, peripheral 0, is granted the bus. However, this
does not change the currently assigned priorities to various peripherals.
Within a peripheral group, the priority is highest for the higher indexed
peripheral (see Table 2-28). For example, of the SPORT pair SP01 (which
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