prim_fair_rr_arb

Arbitrate NUM_IN requesters round-robin through a combinational binary tree.

request_o, data_o, index_o and grant_o are combinational; only the round-robin pointer and the optional lock state are registered. With NUM_IN of 1 the module is a pass-through. Select the arbitration behaviour with these parameters:

FAIR_ARB moves the pointer to the next requesting input after each grant, spreading grants evenly across inputs.
LOCK_IN holds a winner until grant_i completes.
EXT_PRIO replaces the internal RR counter with rr_priority_i so multiple arbiters can share rotating priorities in lock-step; tie rr_priority_i to '0 for static priority, lowest index first. FAIR_ARB and LOCK_IN apply only when EXT_PRIO is 0.
AXI_VLD_RDY treats request/grant as AXI-style valid/ready, so upstream valid must not depend on ready; it reduces arbiter delay and area.

Parameters

Table 1. Parameters
Name	Type	Default	Description
`NUM_IN`	`int unsigned`	`64`	Number of inputs to arbitrate.
`DATA_WIDTH`	`int unsigned`	`32`	Payload width in bits; unused when data_t is overridden.
`EXT_PRIO`	`bit`	`1'b0`	1 overrides the internal RR counter with rr_priority_i. Share rr_priority_i across arbiters for lock-step rotation; tie to '0 for static priority.
`AXI_VLD_RDY`	`bit`	`1'b0`	1 treats request/grant as AXI valid/ready: upstream valid must not depend on ready, and grant_o may assert on the selected input without its request; reduces arbiter delay and area.
`LOCK_IN`	`bit`	`1'b0`	1 freezes the request vector, and so the winning index, while request_o is high and grant_i is low; ignored when EXT_PRIO is 1.
`FAIR_ARB`	`bit`	`1'b1`	1 spreads throughput evenly across inputs; 0 advances the pointer by one per grant. Ignored when EXT_PRIO is 1.
`IdxWidth`	`int unsigned`	`(NUM_IN > 32'd1) ? unsigned'($clog2(NUM_IN)) : 32'd1`	Dependent width of priority and index; do not overwrite.

Ports

Table 2. Ports
Name	Direction	Type	Description
`clk_i`	input	`logic`	Clock, positive-edge triggered.
`rst_ni`	input	`logic`	Active-low reset, sampled synchronously.
`flush_i`	input	`logic`	Synchronously clears the RR pointer and, with LOCK_IN, the lock state; no effect when EXT_PRIO is 1.
`rr_priority_i`	input	`idx_t`	External RR priority; used only when EXT_PRIO is 1.
`request_i`	input	`logic [NUM_IN-1:0]`	Per-port arbitration requests.
`grant_o`	output	`logic [NUM_IN-1:0]`	Per-port grants.
`data_i`	input	`data_t [NUM_IN-1:0]`	Per-port payloads.
`request_o`	output	`logic`	Winning request toward the destination.
`grant_i`	input	`logic`	Destination grant for the winner.
`data_o`	output	`data_t`	Winning payload.
`index_o`	output	`idx_t`	Index of the winning input; valid while request_o is high.