HyperTransport Flow Control: Overview
All of the flow control problems described previously for PCI severely hurt bus performance and would be even less acceptable on a very high-performance connection. The flow control scheme used in HyperTransport applies independently to each transmitter-receiver pair on each link. The basic features include the following.
Packets Never Start Unless Completion Assured
All transfers across HyperTransport links are packet based. No link transmitter ever starts a packet transfer unless it is known the packet can be accepted by the receiver. This is accomplished with the “coupon based” flow control scheme described in this section, and eliminates the need for the Retry and Disconnect mechanisms used in PCI.
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