Directed vs. Broadcast Requests

HyperTransport defines two classes of requests: directed and broadcast. Directed requests travel in the posted or non-posted virtual channel, and always target a particular device. The request destination is indicated either by the address field (e.g. RdSIzed and WrSized requests), or is implied in the request type (Flush and Fence commands target the host bridge). Directed requests move through the chain until they reach the target device and are absorbed. Devices in the path of a directed request forward it to the next device in the direction of the target.

Broadcast requests are issued by bridges and travel in the posted virtual channel. They are accepted by each node then forwarded downstream on all links. When the broadcast request reaches an end-of-chain device, it is absorbed and dropped.

Only the Broadcast Message command type (see Table 11-2 on page 261) uses the broadcast request routing method. All other command types are directed requests.