HyperTransport™ System Architecture

Packet Routing: Shared Bus vs. Point-Point Topology

Routing information in a shared bus topology such as PCI or PCI-X is somewhat simpler than in a point-point topology such as HyperTransport.

Shared Bus Routing

Referring to the PCI/PCI-X shared bus example illustrated in Figure 11-1 on page 258, it should be clear that if a transaction appears on the shared bus, all devices “see it” and have an opportunity to decode the address and command and claim the cycle. Devices other than bridges have no responsibilities for routing information to their neighbors. Also note that arbitration on a shared bus is simple because a single arbiter can manage the entire bus. In PCI/PCI-X, the arbiter is typically in the bus Host Bridge; the arbiter considers ...