Warning: Only a single slice of data found. Did you specify valid 'From/To' times?

Question

I've typed a design code and a testbench code for inverter circuit. The input is of 4 bits, and so is the output. I've tried to display the waveform using:

 $dumpfile("dump.vcd");
 $dumpvars(1);

However, it keeps giving me the message:

Warning: Only a single slice of data found. Did you specify valid 'From/To' times?

Can anybody help me?

Link for my code: https://edaplayground.com/x/EYku

Answer 1

Since no time elapses in your simulation, it is no wonder you get a warning on EDA Playground when you instruct it to display waveforms.

To avoid the warning, uncomment at least one of your delays. Also, you should call $dumpvars at time 0:

module jinvertertb;
  reg [3:0] a;
  wire [3:0] y;

  //Design Instance
  inv jinv(a,y);
  
    initial
    begin
        $dumpfile("dump.vcd");
        $dumpvars;

        $display ("RESULT\ta\ty");

        a = 1; // Another value             
        $strobe("  PASS  \t%d\t%d",a,y);
        #100; //delay
        
        a = 0;             
        $strobe("  PASS  \t%d\t%d",a,y);
        //#100; //delay
      
        a = 4;             
        $strobe("  PASS  \t%d\t%d",a,y);
        //#80
    end
endmodule

This runs without warnings: edaplayground