Flow Control, A System View
While HyperTransport flow control is enforced on a per-link basis, there are system implications if it does not perform properly. As a point-point technology, HyperTransport devices such as tunnels and bridges have responsibilities for generating their own packets upstream as well as forwarding those from devices either above or below them. Refer to Figure 5-2 on page 106. Note that when the peripheral at the bottom of the chain on the right issues a packet upstream towards memory, it is dependent on how well the devices above manage their links.
Figure 5-2: Flow Control Is On A Link-By-Link Basis