// File:  testbench.v// Date:  01/01/2005// Name:  Eric Crabill// // This is a top level testbench for the// loopback design, which is part of the// EE178 Lab #4 assignment.// The `timescale directive specifies what// the simulation time units are (1 ns here)// and what the simulator timestep should be// (1 ps here).`timescale 1 ns / 1 psmodule loopback_testbench_v_tf();  // Declare wires to be driven by the outputs  // of the design, and regs to drive the inputs.  // The testbench will be in control of inputs  // to the design, and will check the outputs.  // One exception here is the serial port loop.  // Then, instantiate the design to be tested.  reg rs232;  wire [7:0] leds;  reg [7:0] switches;  reg clk, rst;  loopback my_loopback (        .clk(clk),         .rst(rst),         .leds(leds),         .switches(switches),         .rs232_tx(rs232),         .rs232_rx(rs232),		  .lock()        );  // Describe two processes that generate clock  // and reset signals.  The clock is 50 MHz, and  // let's assume the reset button is pressed at  // time zero for a short period of time, then  // released.  always  begin    clk = 1'b1;    #10;    clk = 1'b0;    #10;  end  initial  begin    rst = 1'b0;    #110;    rst = 1'b1;  end  // Task for waiting an arbitrary  // number of system clock cycles.  task CYCLE_WAIT;    input [31:0] cycles;    integer cyc_cnt;  begin    cyc_cnt = cycles;    while (cyc_cnt)    begin      cyc_cnt = cyc_cnt - 1;      @(posedge clk);    end  end  endtask
  
 
  
  
 
    // Assign values to the input signals and  // check the output results.  This template  // is meant to get you started, you can modify  // it as you see fit.  If you simply run it as  // provided, you will need to visually inspect  // the output waveforms to see if they make  // sense...  initial  begin    $display("If simulation ends prematurely, restart");    $display("using 'run -all' on the command line.");    switches <= 8'b00000000;    // Wait until reset is deasserted.    @(posedge rst);    $display("Reset is deasserted...");    // Wait for a while, this is time to let the cold    // reset code execute on picoblaze before the main    // loop begins to execute.    CYCLE_WAIT(1000);    // Apply a pattern to the switches and then check    // that it appears on the LEDs after a short time.    switches <= 8'b10101010;    CYCLE_WAIT(20);    if (leds == switches) $display("PASS: LEDs equal switches.");    else $display("FAIL: LEDs do not match switches.");    // Apply a pattern to the switches and then check    // that it appears on the LEDs after a short time.    switches <= 8'b01010101;    CYCLE_WAIT(20);    if (leds == switches) $display("PASS: LEDs equal switches.");    else $display("FAIL: LEDs do not match switches.");    // Wait for a while, this is time to let the rs232    // interface shuffle some bits around.  There should    // be activity on the rs232 signal.    CYCLE_WAIT(1000);    // End the simulation.    $display("Simulation is over, check the waveforms.");    $stop;  endendmodule