Bus Arbitration Priority (Rpba) - Analog Devices SHARC ADSP-21368 Hardware Reference Manual

Shared Memory Interface

Bus Arbitration Priority (RPBA)

To resolve competing bus requests, there are two available priority
schemes—fixed and rotating. The
is high, rotating priority bus arbitration is selected, and when
fixed priority is selected. The
each processor in a multiprocessing system.
In the fixed priority scheme, the processor with the lowest
among the competing bus requests becomes the bus master. If, for exam-
ple, the processor with
the bus simultaneously, the processor with
the following cycle.
Each processor knows the
bus, because the
processor.
The rotating priority scheme gives roughly equal priority to each proces-
sor. When rotating priority is selected, the priority of each processor is
reassigned after every transfer of bus mastership. Highest priority is
rotated from processor to processor as if they were arranged in a circle—
the processor with the next highest
is the one that receives highest priority.
how rotating priority changes on a cycle-by-cycle basis.
Table 3-31. Rotating Priority Arbitration Example
Cycle Number
2
1
2
3
3-86
RPBA
pin must be set to the same value on
RPBA
= 010 and the processor with
ID
ID
corresponds to the
ID
ID
Hardwired Processor IDs and Priority
ID1 ID2
M 1
2 3-BR
2 3-BR
ADSP-21368 SHARC Processor Hardware Reference
pin selects the scheme. When
=010 becomes bus master in
ID
of the other processors requesting the
line being used for each
BRx
setting from the current bus master
Table 3-31 shows an example of
1
ID3
2-BR
M-BR
M
RPBA
is low,
RPBA
number
ID
=100 request
ID
ID4
3
1
1