Added command signal driver module

verification/sd/send_command_tb.sv

@@ -0,0 +1,63 @@
+module send_command_tb;
+
+bit clk;
+// The crc should be clocked way faster than the sender
+bit crc_clk;
+logic reset;
+logic start;
+logic [5:0] command;
+logic [31:0] arguments;
+wire ready;
+wire sd_cmd;
+
+logic [47:0] fill_me;
+int counter;
+
+logic sd_cmd_real;
+
+assign sd_cmd_real = (sd_cmd === 'z) ? 1 : 0;
+
+send_command dut(.*);
+
+initial forever #100 clk = ~clk;
+initial forever #20 crc_clk = ~crc_clk;
+
+
+
+initial begin
+    reset = 1;
+    start = 0;
+
+    repeat (2) @(posedge clk);
+
+    reset = 0;
+    @(posedge clk);
+
+    start = 1;
+    command = 8;
+    arguments = 'h1AA;
+
+    counter = 48;
+
+    @(posedge clk);
+
+    // Try receiving the CMD8
+    while (counter != 0) begin
+        // Check for the start bit, or that we're receiving a message
+        if (sd_cmd_real != 1 || counter != 48) begin
+            fill_me = {fill_me[46:0], sd_cmd_real};
+            counter--;
+        end
+        @(posedge clk);
+    end
+
+    assert (fill_me === {2'b01, 6'd8, 32'h1AA, 8'h87})
+        else $error("Received wrong command, got 0x%x",fill_me);
+
+    assert (ready)
+        else $error("SD command sender not ready");
+
+
+    $finish;
+end
+endmodule