Packet Switching - 2021.2 English

Versal ACAP AI Engine Programming Environment User Guide (UG1076)

Document ID
English (United States)
Release Date
2021.2 English

Packet Stream connections have a field known as the packet ID. If the source of the packet ID field comes from within the ADF graph, the x86 simulator uses the canonical, zero-based indexing scheme for packet IDs. The first branch on the output of a split node has a packet ID equal to 0 followed by 1, 2, 3, etc. If the source of the packet ID field comes from outside the ADF graph there will be discrepancies between the AI Engine simulator and the x86 simulator. To resolve these discrepancies see Packet Switching and the AI Engine Simulator for additional information on providing custom packet IDs when the source is outside the ADF graph.

The nature of packet merging means that the x86 simulator and the AI Engine simulator produce non-deterministic results. If an AI Engine on a packet split branch finishes processing data before any of the other branches its data appears on the output of the packet merge first. Exactly which core finishes first is highly dependent on both the kernel code and the incoming data. So any downstream processing blocks must be prepared to handle this behavior.