Pci Bus Arbiter - Toshiba TMPR4937 Manual

10.3.12 PCI Bus Arbiter

Configuration settings (DATA[2] signal) during boot up select whether to use the on-chip PCI Bus
arbiter (Internal PCI Bus Arbiter mode) or to use the External PCI Bus arbiter (External PCI Bus Arbiter
mode).
When in the Internal PCI Bus Abiter mode, setting the PCI Bus Arbiter Enable bit
(PBACFG.PBAEN) of the PCI Bus Arbiter Configuration Register starts operation.
The on-chip PCI Bus arbiter can arbitrate eight sets of PCI Bus usage requests from the Bus Master.
Five ports are used: one for the PCI Controller bus master and four for External Bus masters. The three
remaining ports are reserved for future expanded features.
10.3.12.1 Request Signal, Grant Signal
The four external Bus Masters are connected to the REQ[3:0] signal and the GNT[3:0]* signal.
Also, when in the External PCI Bus Master mode, the REQ[0]* signal becomes the PCI Bus
Request Output signal and the GNT[0]* signal becomes the Bus Usage Permission Input Signal.
Furthermore, the REQ[1]* signal can be used as an interrupt output signal to the external devices
(see 14.3.7 for more information).
10.3.12.2 Priority Control
As illustrated below in Figure 10.3.8, a combination of two round-robin sequences is used as
the arbitration algorithm that determines the priority of Internal PCI Bus arbiter bus requests. The
round-robin with the lower priority (Level 2) consists of Masters W - Z, and the round-robin with
the high priority (Level 1), consists of Master A - D and Level 2 Masters. The PCI Bus Arbiter
Request Port Register (PBAREQPORT) specifies whether to allocate the PCI Controller and the
four External Bus Masters to Masters A-D or W - Z.
Level 1
(Prirority: High)
Level 2
(Priority: Low)
Master B
Master A
Master Z
Figure 10.3.8 PCI Bus Arbitration Priority
10-20
Chapter 10 PCI Controller
Master C
Master D
Level 2
Master W
Master X
Master Y