Arbitration Logic - Microarchitecture of Network-on-Chip Routers - page 65

Fig. 4.6 The round-robin arbiter selects the rightmost maximum symbol. Even if there are no
active requests in the HP segment, no cyclic-priority transfer is needed, and the first request of the
LP segment is given at the output

implicitly implements the cyclic transfer of the priority from the HP to the LP
segment, without requiring any true cycle in the circuit.
The round-robin arbiter that follows this algorithm, is built using a set of small
comparison nodes. Each node receives two arithmetic symbols, one coming from the
left and one from the right side. The maximum of the two symbols under comparison
appears at the output of each node. Also, each node generates one additional control
flag that denotes if the left or the right symbol has won, i.e., it was the largest. In
case of a tie, when equal symbols are compared, this flag always points to the right.
In this way, the first (rightmost) symbol is propagated to the output as dictated by the
operation of the arbiter. Two examples of the comparison procedure that implements
implicitly the cyclic search of a round-robin arbiter are illustrated in Fig. 4.6 .
The associated grant generation logic is exactly the same as the one shown in
Fig. 4.3 . No change is required since, in both cases, the grants are generated based
solely on the local direction flags F and are independent of the operation of the
maximum-selection nodes.

4.2.1 Merging Round-Robin Arbitration with Multiplexing

In every case, the winning path that connects the winning input with the output is
defined by the direction flags of the MAX nodes. Thus, if we use these flags to