A54SX16-2 Datasheet, PDF (2/4 Pages) Actel Corporation – PCI Arbiter Core

Arbitration Schemes
Pure rotation is a turn-based method that allows each bus
master one transaction in turn if multiple masters are
requesting the bus simultaneously. If only one master
requests the bus, that master will immediately get the grant.
Figure 3 illustrates the pure rotation scheme.
Fair rotation is employed if an embedded processor is
required to initialize the system but will not be used after
that point. By giving it highest priority, the fair rotation
scheme allows the embedded processor access to the PCI
bus on every other transaction when it is requesting the bus
continuously. The other masters use a pure rotation scheme.
The fair rotation scheme is illustrated in Figure 4.
IDLE
Device 0
Device 4
Device 1
Device 3
Figure 3 • Pure Rotation Arbitration
Device 2
Device 4
Device 1
Device 0
IDLE
Device 3
Figure 4 • Fair Rotation Arbitration
2
Device 2
v4.0