The messaging system connects eight agents together in a mesh configuration. The PL is represented by four agents, and the PMU is one agent. The message passing between agents can be done exclusively between the sender and receiver using all 128 of the 32B permission apertures in the XPPU.
To support message passing, the software in the two processors must pre-define the format of the request and response message buffers. The buffer content does not affect the hardware. The use of a message buffer is optional. This Figure shows the IPI message passing architecture.