add counter

counter/counter_tb.v

@@ -0,0 +1,44 @@
+`include "./counter/counter.v"
+
+module counter_tb;
+    reg clk, rst, write_enable;
+    reg [15:0] write_value;
+    wire [15:0] count;
+
+    counter #(.N(16)) cnt(
+        .clk(clk),
+        .rst(rst),
+        .write(write_enable),
+        .write_value(write_value),
+        .count(count)
+    );
+
+    initial clk = 0;
+    always #5 clk = ~clk;
+
+    initial begin
+        $dumpfile("./counter/counter.vcd");
+        $dumpvars(0, counter_tb);
+
+        rst = 1; write_enable = 0; write_value = 0;
+        @(posedge clk); #1
+        rst = 0;
+
+        // Contar 20 ciclos
+        repeat(20) @(posedge clk);
+        #1 $display("despues de 20 ciclos: count=%0d", count);
+
+        // Load a 200
+        write_enable = 1; write_value = 200;
+        @(posedge clk); #1
+        write_enable = 0;
+        $display("tras load 200: count=%0d", count);
+
+        // Contar hasta overflow (56 ciclos llega a 255 y desborda a 0)
+        repeat(60) @(posedge clk);
+        #1 $display("tras 60 ciclos mas: count=%0d", count);
+
+        $finish;
+    end
+
+endmodule