plru_tree: Assert output is onehot (#206)

* plru_tree: Assert output is onehot

* plru_tree: Use system function for onehot assertion

* plru_tree: Add missing closing parenthesis

Co-authored-by: Nils Wistoff <[email protected]>

Author: michael-platzer

src/plru_tree.sv

@@ -123,6 +123,10 @@ module plru_tree #(
     initial begin
         assert (ENTRIES == 2**LogEntries) else $error("Entries must be a power of two");
     end
+
+    output_onehot : assert property(
+        @(posedge clk_i) disable iff (~rst_ni) ($onehot0(plru_o)))
+        else $fatal (1, "More than one bit set in PLRU output.");
 `endif
 // pragma translate_on