The Packet-Based Protocol
HyperTransport employs a packet-based protocol in which all information —address, commands, and data — travel in packets which are multiples of four bytes each. Packets are used in link management (e.g. flow control and error reporting) and as building blocks in constructing more complex transactions such as read and write data transfers.
It should be noted that, while packet descriptions in this chapter are in terms of bytes, the link's bidirectional interface width (2, 4, 8, 16, or 32 bits) ultimately determines the amount of packet information sent during each bit time on HyperTransport links. There are two bit times per clock period.
Before looking at packet function and use, the following sections describe the mechanics ...
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