Chapter 8: PCI/G-Bus Bridge
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
8-15
8.2.11 PCI Bus Arbiter
The PCI Bus Arbiter supports up to five Masters on the PCI Bus, including the PGB. The
Arbiter may be enabled or disabled through the G-Bus to allow an external arbiter to be used.
8.2.11.1
PCI Bus Priority
All masters have the same round robin priority.
8.2.11.2
Arbiter Bus Parking
The PCI Bus will be parked at the last Master to have a successful data phase.
8.2.11.3 Retried
Masters
When a Master on the PCI Bus is retried, the Arbiter gives ownership of the bus to another
Master with active ARB_REQ* signal.
8.2.11.4
Failed Master Lockout
If a Master does not use the PCI Bus for at least 16 PCI clocks after it is granted the bus, it
is assumed broken and the Arbiter stops granting it the bus.
8.2.11.5 PCI
Arbiter
Implementation
The TX7901 allows both internal and external arbiters.
In the case of internal arbiters, PGB requests are connected to Port0 of the arbiter, so there
is no need to make a connection to the outside of the chip. In contrast, it is required that
Gnt0, a grant from arbiter, is connected to PGB’s Gnt outside of the chip. In the single PCI
configuration, PCI0 has five ports of arbiter pins outside the chip. In the Dual PCI
configuration, PCI0 and PCI1 both have three ports. These arbiter pins are shared in order
to save package pins.
In the case of external arbiters, the user may connect Req and Gnt to the user’s own
arbiters. All the Request signals of internal arbiter, should be connected to 0.
Содержание TMPR7901
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