adding stream arbiter

hw/rtl/libs/VX_fair_arbiter.v

@@ -1,17 +1,20 @@
 `include "VX_platform.vh"
 
 module VX_fair_arbiter #(
-    parameter N = 1
+    parameter NUM_REQS     = 1,
+    parameter LOCK_ENABLE  = 0,
+    parameter LOG_NUM_REQS = $clog2(NUM_REQS)
 ) (
-    input  wire                  clk,
-    input  wire                  reset,
-    input  wire [N-1:0]          requests,           
-    output wire [`LOG2UP(N)-1:0] grant_index,
-    output wire [N-1:0]          grant_onehot,   
-    output wire                  grant_valid
+    input  wire                     clk,
+    input  wire                     reset,
+    input  wire [NUM_REQS-1:0]      requests,           
+    input  wire                     enable,
+    output wire [LOG_NUM_REQS-1:0]  grant_index,
+    output wire [NUM_REQS-1:0]      grant_onehot,   
+    output wire                     grant_valid
   );
 
-    if (N == 1)  begin                
+    if (NUM_REQS == 1)  begin                
         
         `UNUSED_VAR (clk)
         `UNUSED_VAR (reset)
@@ -21,49 +24,40 @@ module VX_fair_arbiter #(
 
     end else begin    
 
-       reg  [N-1:0] requests_use;
-       wire [N-1:0] update_value;
-       wire [N-1:0] late_value;
-
-       wire         refill;
-       wire [N-1:0] refill_value;
-       reg  [N-1:0] refill_original;
+       reg  [NUM_REQS-1:0] remaining;       
+       wire [NUM_REQS-1:0] remaining_next;
+       wire [NUM_REQS-1:0] requests_use;
+       reg  use_buffer;     
 
        always @(posedge clk) begin
             if (reset) begin
-                requests_use    <= 0;
-                refill_original <= 0;
-            end else begin
-                if (refill) begin
-                    requests_use    <= refill_value;
-                    refill_original <= refill_value;
-                end else begin
-                    requests_use <= update_value;
-                end
+                remaining  <= 0;
+                use_buffer <= 0;
+            end else if (!LOCK_ENABLE || enable) begin
+                remaining  <= remaining_next;
+                use_buffer <= (remaining_next != 0);
             end
-       end
+        end
 
-       assign refill       = (requests_use == 0);
-       assign refill_value = requests;
+        assign requests_use = use_buffer ? remaining : requests;
         
-        reg [N-1:0] grant_onehot_r; 
-
         VX_priority_encoder #(
-            .N(N)
+            .N(NUM_REQS)
         ) priority_encoder (
             .data_in   (requests_use),
             .data_out  (grant_index),
             .valid_out (grant_valid)
         );
 
+        reg [NUM_REQS-1:0] grant_onehot_r;
         always @(*) begin
-            grant_onehot_r = N'(0);
+            grant_onehot_r = NUM_REQS'(0);
             grant_onehot_r[grant_index] = 1;
         end
-        assign grant_onehot = grant_onehot_r;    
-        assign late_value   = ((refill_original ^ requests) & ~refill_original);
-        assign update_value = (requests_use & ~grant_onehot_r) | late_value;
 
+        assign remaining_next = requests_use & ~grant_onehot_r;
+
+        assign grant_onehot = grant_onehot_r;
     end
     
 endmodule