User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 8: PCI Bus and HyperTransport Fabric Page
191
shows the physical and logical organization of the PCI and HyperTransport interfaces.
Figure 36: PCI and HyperTransport Organization
Physically the PCI and HyperTransport interfaces are both connected to ZBbus through I/O bridge 0 (as shown
on the left in
). The I/O bridge implements the ZBbus protocol, and includes the address and data
buffers for transactions between the ZBbus and each interface, the buffers for peer-to-peer transfers between
the PCI and HyperTransport, and the buffer for merging partial cache line writes. The PCI and HyperTransport
interface units implement their respective bus protocols, and include additional data and command buffering.
The bandwidths of the connections between the I/O bridge and interface units are sized appropriately for the
interfaces, so the HyperTransport is not constrained by the PCI bandwidths.
However, the interfaces are presented logically to the system as if the HyperTransport was bridged from the
PCI bus (shown on the right of
). This makes the PCI always bus zero to the device enumeration code
(this is required by some software) and allows configuration to be based on existing code.
ZBbus
ZBbus
IO Bridge 0
PCI
Interface
HT
Interface
PCI
Bus
HT
Fabric
Device A
Device B
Device C
Device D
Device
E
Device
F
Device
E
Device
F
PCI
Host Bridge
HT
Bridge
Device
A
Device
B
Device
C
Device
D
Bus 1
Physical View
Logical View
Bus 0