adding input buffering to bus arbiters to reduce backpressure delay propagation

hw/rtl/libs/VX_fixed_arbiter.v

@@ -26,21 +26,24 @@ module VX_fixed_arbiter #(
 
     end else begin
     
-        VX_priority_encoder # (
-            .N(NUM_REQS)
-        ) priority_encoder (
-            .data_in   (requests),
-            .data_out  (grant_index),
-            .valid_out (grant_valid)
-        );
-
+        reg [LOG_NUM_REQS-1:0] grant_index_r;
         reg [NUM_REQS-1:0] grant_onehot_r;
-        always @(*) begin
-            grant_onehot_r = NUM_REQS'(0);
-            grant_onehot_r[grant_index] = 1;
-        end
 
+        always @(*) begin
+            grant_index_r  = 'x;
+            grant_onehot_r = 'x;
+            for (integer i = 0; i < NUM_REQS; ++i) begin            
+                if (requests[i]) begin
+                    grant_index_r  = LOG_NUM_REQS'(i);
+                    grant_onehot_r = NUM_REQS'(1) << i;
+                    break;
+                end
+            end
+        end      
+
+        assign grant_index  = grant_index_r;
         assign grant_onehot = grant_onehot_r;
+        assign grant_valid  = (| requests);
     end
     
 endmodule