AXI4

This is also stated in the original AXI(3) protocol. The AXI protocol only describes the signals to connect a single master to a single slave, so a point to point connection.

So in a multi-master, multi-slave system you need an interconnect structure not defined by the protocol.

The connection from an AXI master to this interconnect connects to an AXI slave port on the interconnect, and the connections from the interconnect to an AXI slave are from an AXI master port on the interconnect. So again all the master-slave connections are point to point, and it is then how this interconnect functions that is not defined.

Compare this to the older AHB protocols where every system component between master and slave were defined, so an arbiter, an address decoder, master to slave mux, slave to master mux. So AHB is not a point to point protocol, and clearly defines how each system component should function.

AXI system structures are not defined, allowing the user more flexibility in how they build their system. All that is required is that each master to slave connection fully complies with the simpler protocol requirements.

Whether or not you agree that this is a good idea is up for debate as building an AXI interconnect is not easy at all, but trying to define how an AXI interconnect should function in a protocol document would result in a MASSIVE document, so this probably is the best approach.

This is also stated in the original AXI(3) protocol. The AXI protocol only describes the signals to connect a single master to a single slave, so a point to point connection.

So in a multi-master, multi-slave system you need an interconnect structure not defined by the protocol.

The connection from an AXI master to this interconnect connects to an AXI slave port on the interconnect, and the connections from the interconnect to an AXI slave are from an AXI master port on the interconnect. So again all the master-slave connections are point to point, and it is then how this interconnect functions that is not defined.

Compare this to the older AHB protocols where every system component between master and slave were defined, so an arbiter, an address decoder, master to slave mux, slave to master mux. So AHB is not a point to point protocol, and clearly defines how each system component should function.

AXI system structures are not defined, allowing the user more flexibility in how they build their system. All that is required is that each master to slave connection fully complies with the simpler protocol requirements.

Whether or not you agree that this is a good idea is up for debate as building an AXI interconnect is not easy at all, but trying to define how an AXI interconnect should function in a protocol document would result in a MASSIVE document, so this probably is the best approach.