2.11.4. QoS Virtual Networks (QVN)

QVN is a technology that enables transactions that are associated with different virtual networks and makes independent progress possible from a source to a destination. This ensures that a transaction on one Virtual Network (VN) can progress towards its destination even if a transaction on a different VN is blocked.

If an interconnect supports QVN, the use of physical wires to send a transfer is negotiated before the transfer is sent. This ensures that when a transfer is sent on the physical wires it is guaranteed to be accepted.

The QVN protocol provides extensions to the AMBA protocol to enable the support of virtual networks within the AXI3, AXI4, ACE, and ACE-Lite bus infrastructures. Using virtual networks and tokens improves system performance because it stops high-bandwidth AXI and ACE sources from preventing the flow of latency critical transactions.

CCI-400 supports QVN on read and write channels of master and slave interfaces. Each slave interface can be assigned to one of four virtual networks. Each master interface supports up to four virtual networks. Each virtual network on the master interfaces can be configured to have a pre-allocated token. If a virtual network does not have a pre-allocated token, there is a minimum 2-cycle delay for each request while the virtual network requests and is granted a token.

See the ARM® CoreLink™ QVN Protocol Specification for more information.

Note

The ARM® CoreLink™ QVN Protocol Specification is available from ARM. This is a confidential document and a separate license is required.

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