Electronic Design

Three Routing Options

Path Routing: This can be thought of as StarGen's native routing method. StarGen converts the PCI address in the PCI fabric bridge into a path specification. The path specifies how the traffic is to be routed at each star. The path also specifies for each star, between its source and the destination, which output ports the traffic is to exit. This is also known as source-based routing. Because StarGen uses source-based routing, there is no need for routing tables in the switch.

Multicast Routing: In the case of multicast traffic, one source talks to multiple destinations. StarGen relies on multicast tables in the switch. When multicast traffic arrives at a star, a lookup is performed using a resident lookup table maintained by software. This specifies which output ports to use for the multicast traffic.

Address Routing: Address routing is provided so StarGen is fully compatible with PCI. Transactions are routed in a PCI environment, based on the address of the transaction. Each bridge in the hierarchy examines the address of the transaction and makes a decision to route the transaction across the bridge.

PCI systems have a flat global address space that is partitioned across the various buses that appear in the bus topology (hierarchy). If there are multiple buses in a PCI system, there is a subset of the total system address space on each bus.

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