A–30
System Address Space
PCI Configuration Space
archically behind it. If the bus number of the configuration cycle matches the bus num-
ber of the bridge chip’s secondary PCI interface, it will accept the configuration cycle,
decode it, and generate a PCI configuration cycle with ad<1:0> = 00 on its secondary
PCI interface. If the bus number is within the range of bus numbers that may exist
hierarchically behind its secondary PCI interface, the bridge chip passes the PCI con-
figuration cycle on unmodified (ad<1:0> = 01). It will be accepted by a bridge further
downstream. Figure 1–16 shows a typical PCI hierarchy. This is only one example of
how the 21174 can be used in a system design.
Figure 1–16 PCI Bus Hierarchy
LJ-05401.AI4
SCSI
SCSI
SCSI
Ethernet
PCI-to-PCI
Bridge
Memory
Bcache
PCI
Graphics
32-Bit
Slots
Slot
Slot
Slot
Audio
PCI-to-(E)ISA
Bridge
(E)ISA
Bus
64-Bit Slots
Internal PCI
64-Bit PCI Bus
21164
21174
ASIC