- Networks must be hierarchically composable. Topology must form DAG.
- MOESI-equivalent protocol
- Channel A : M-S : Request
- Channel D : S-M : Data response
- Channel B : M-S : Snoop (Request that an operation to be performance at an address cached by a master, accessing, or writing back that cached data)
- Channel C : S-M : Snoop acknowledge
- Channel E : M-S : Final acknowledgement
Priority of messages is A, B, C, D, E. In order of increasing priority.
Each channel is implemented as physically independent. Data payload may need to be spread out across beats (clock cycles). Multi-beat message often called a burst. Messages without data payload must always be exchanged in a single beat.
Flow control done using ready-valid handshaking. Valid may never depend on ready. The sender must assert valid independently of whether the receiver signals that it is ready. Conditions for beats appear in spec.
Specification gives forward progress rules.
To be continued ...