Prevention of Head-of-Line Blocking

Zynq UltraScale+ Device Technical Reference Manual (UG1085)

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2.4 English

Head-of-line blocking (HOLB) can occur when two or more different traffic classes share the same physical channel. A typical example is when a low-priority request cannot make progress and a high priority request is blocked behind it. HOLB is prevented with the following guidelines.

Have two ports between the CCI-400 and the DDR controller carry two QoS virtual network channels (QVN) per physical channel.

On all other DDR controller ports, assign only one class of traffic to each port.