Intel® Arria® 10 Hard Processor System Technical Reference Manual

ID 683711
Date 1/10/2023
Public

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8.2.11.2.2. Pressure Propagation

Each active datapath in the interconnect has a pressure level, which is the highest urgency of all packets currently in the datapath. Pressure can change depending on the traffic through the datapath.

The pressure is based on the urgency of packets waiting for that datapath. If a higher-priority packet requests a datapath that is already active, the datapath’s urgency increases.

When a packet arrives at an arbitration node, normally its priority is the urgency assigned by its master. However, if the datapath's pressure is greater than the urgency, that pressure tells the node that there is a higher-urgency packet somewhere behind the current one. This prompts the node to expedite the lower-urgency packet to free up the datapath.

For example, consider three active packets in the interconnect. Packets A and B are moving through the same datapath, with A ahead of B. Packet C is on a different datapath.

Packet A's urgency value is 1, and packet B's urgency is 3. Packet A arrives at a particular node simultaneously with Packet C—and Packet C's urgency is 2. Without the pressure mechanism, Packet C would pass through the node first, ahead of Packet B, even though Packet B has the highest urgency of the three packets.

However, because Packet B's urgency is 3, its datapath has a pressure of 3. That pressure value tells the node to accept the packet on that datapath—Packet A—even though it has a lower urgency. After Packet A is out of the way, the node can accept Packet B ahead of Packet C.