An AXI interface consists of a standard set of logic signals as defined by Arm® in the AMBA® AXI and ACE Protocol Specification and AMBA® 4 AXI4-Stream Protocol Specification. These signals convey the data transactions encoded as logic events as described by the specification. The Vivado simulator makes those signals available for viewing directly in the wave viewer, however, it can be difficult to visualize what transactions are happening from the signals alone.
To make it easier to view the transactions, the Vivado simulator provides a feature that analyzes the signal activity and produces new signals that summarize the activity at the transaction level. This process is called as protocol analysis. For each AXI interface the Vivado simulator creates a new design object called a protocol instance that represents the AXI interface and the inputs and outputs of protocol analysis. The protocol instance typically resides in the same scope as its input signals.