ADSP-21368 SHARC Processor Hardware Reference 2-21
I/O Processor
IOP channel arbitration can be set to use either a fixed or rotating algo-
rithm by setting or clearing bit 7 (
DCPR) in the SYSCTL register:
•fixed SYSCTL[7] cleared (0)
• rotating SYSCTL[7] set (1)
In the fixed priority scheme, the lower indexed peripheral has the highest
priority.
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. Peripheral groups are shown in
Table 2-5.
Initially, group A has the highest priority and group F 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 2-5). For example, in SP01 (which is in group A),
SP1 has the highest priority.
Table 2-5. DMA Channel Allocation and Parameter Register
Assignments
DMA
Channel
Number
Data Buffer Group IOP Address of
Data Buffers
Description
0 (highest
priority)
RXSP1A, TXSP1A A 0xC65, 0xC64 Serial Port 1A Data
1 RXSP1B, TXSP1B A 0xC67, 0xC66 Serial Port 1B Data
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