1 files changed, 77 insertions, 0 deletions
diff --git a/tb/rot13_tb.v b/tb/rot13_tb.v
new file mode 100755
index 0000000..1ec21c4
--- /dev/null
+++ b/tb/rot13_tb.v
@@ -0,0 +1,77 @@
+`timescale 1ns/1ps
+module rot13_tb;
+
+reg synth_clk_12mhz;
+always @(synth_clk_12mhz) begin
+    #41.6665 synth_clk_12mhz <= ~synth_clk_12mhz;
+end
+
+initial begin
+    // the first event that sets the clock in motion
+    #0 synth_clk_12mhz <= 1'b0;
+end
+
+reg reset;
+integer nfail;
+
+reg [7:0]  in_char;
+wire [7:0] out_char;
+
+rot13 rot13_inst (
+    .clock(synth_clk_12mhz),
+    .reset(reset),
+    .in_char(in_char),
+    .out_char(out_char)
+);
+
+task check_rot13;
+    input [7:0] a;
+    input [7:0] b;
+    begin
+        in_char <= a;
+        #100 // 100 ns delay
+        if (out_char !== b) begin
+            nfail = nfail + 1;
+            $display("FAIL: '%c' -> '%c' (got '%c')", a, b, out_char);
+        end else begin
+            $display("'%c' -> '%c'", a, out_char);
+        end
+    end
+endtask
+
+initial begin
+    nfail = 0;
+    $display("=================== start %m");
+    #0
+    reset <= 1'b1;
+    #1000
+    reset <= 1'b0;
+    #100
+
+    check_rot13("A", "N");
+    check_rot13("a", "n");
+    check_rot13("N", "A");
+    check_rot13("n", "a");
+    check_rot13("M", "Z");
+    check_rot13("m", "z");
+    check_rot13("Z", "M");
+    check_rot13("z", "m");
+    check_rot13(".", ".");
+    check_rot13("8", "8");
+    check_rot13("@", "@");
+    check_rot13("[", "[");
+    check_rot13("`", "`");
+    check_rot13("{", "{");
+
+    // uncomment the below to ensure failures are caught
+    //check_rot13("a", "a");
+
+    if (nfail !== 0) begin
+        $display("=================== %m: FAIL (%d problems)", nfail);
+    end else begin
+        $display("=================== %m: PASS");
+    end
+    $finish();
+end
+
+endmodule