AXI4-Stream Position Bytes

Question

Can someone explain what a position byte is in the context of the AXI4-Streaming interface? I don't understand how, while it's not the same as a null byte, it doesn't have to transmitted to the slave.

Answer 1

Unfortunately, AXI4 streaming specification does not provide examples for position use-case. Anyway, based on my understanding, position bytes are inserted at the master/source for those slaves that work based on position of received bytes.

For example, in a given system, a master and slave may assume a certain protocol to be followed in the streaming interface. Say, every 4 bytes would indicate start of certain data and valid for 3 bytes. Hence you have a layout of data such that you would have a predefined data starting every 4 bytes but only 3 out of those 4 bytes (first 3) would be of any use to the slave.

If a particular slave does not support position byte then the interconnect has to remove this before transmitting to the slave.