Add testbench for axis_loopback topfile

Doesn't do anything except to test for any warnings/errors etc. in the full
system.

hdl/top/axis_loopback_tb.v

@@ -0,0 +1,132 @@
+/**
+ * Testbench:
+ *  axis_loopback
+ *
+ * Created:
+ *  Sun Jun  3 14:42:30 PDT 2018
+ *
+ * Author:
+ *  Berin Martini (berin.martini@gmail.com)
+ */
+
+`timescale 1ns/10ps
+
+`define TB_VERBOSE
+//`define VERBOSE
+
+
+`include "axis_loopback.v"
+
+module axis_loopback_tb;
+
+    /**
+     * Clock and control functions
+     */
+
+    // Generate a clk
+    reg clk;
+    always #1 clk = !clk;
+
+    // End of simulation event definition
+    event end_trigger;
+    always @(end_trigger) $finish;
+
+`ifdef TB_VERBOSE
+    // Display header information
+    initial #1 display_header();
+    always @(end_trigger) display_header();
+
+    // And strobe signals at each clk
+    always @(posedge clk) display_signals();
+`endif
+
+//    initial begin
+//        $dumpfile("result.vcd"); // Waveform file
+//        $dumpvars;
+//    end
+
+
+    /**
+     * Local parameters
+     */
+
+
+`ifdef TB_VERBOSE
+    initial $display("Testbench for unit 'axis_loopback'");
+`endif
+
+
+    /**
+     *  signals, registers and wires
+     */
+
+    reg rst;
+
+
+    /**
+     * Unit under test
+     */
+
+    axis_loopback
+    uut (
+        .clk    (clk),
+        .rst_n  ( ~rst)
+    );
+
+
+    /**
+     * Wave form display
+     */
+
+    task display_signals;
+        $display(
+            "%d\t%d",
+            $time, rst,
+
+        );
+
+    endtask // display_signals
+
+    task display_header;
+        $display(
+            "\t\ttime\trst",
+
+        );
+    endtask
+
+
+    /**
+     * Testbench program
+     */
+
+    initial begin
+        // init values
+        clk = 0;
+        rst = 0;
+        //end init
+
+`ifdef TB_VERBOSE
+    $display("RESET");
+`endif
+
+        repeat(6) @(negedge clk);
+        rst <= 1'b1;
+        repeat(6) @(negedge clk);
+        rst <= 1'b0;
+        @(negedge clk);
+
+
+`ifdef TB_VERBOSE
+    $display("wait");
+`endif
+
+        repeat(10) @(negedge clk);
+
+
+`ifdef TB_VERBOSE
+    $display("END");
+`endif
+        -> end_trigger;
+    end
+
+endmodule