CODEWITHSUNDEEP
verilog
CD4
CD4

Reputation: 15

"Not a valid l-value" Error in Verilog

I am new to Verilog (and, to a lesser extent, programming) and am trying to create a program that finds the absolute value of a set of numbers and then calculates for a running average. The running average is 5 points wide, and goes across a data set that is about 40 numbers wide.

I am having trouble with the running average (lines 14-17 design, 24-28 test-bench) and am receiving the errors "o2/out is not a valid l-value in tb.avg." and "o2/out is declared here as a wire". How should I fix this?

Here is my design:

module absolute_value(i1,o1);
  input signed [11:0] i1;
  output signed [11:0] o1;

  assign o1 = i1[11] ? -i1 : i1;
endmodule 

module moving_average(k1,k2,k3,k3,k4,o2,out);
  input k1, k2, k3, k4, k5;
  output [11:0] o2;
  output [11:0] out;
  integer t;

  always begin
    assign o2 = (k1 + k2 + k3 + k4 + k5) / 5;
    assign out = o2;
  end
endmodule

And here is my test-bench:

module tb;
  reg signed [11:0] i1;
  wire signed [11:0] o1;

  reg k1;
  reg k2;
  reg k3;
  reg k4;
  reg k5;
  wire [11:0] o2;
  wire [11:0] out;

  absolute_value abs(i1,o1);  
  moving_average avg(k1,k2,k3,k4,k5,o2,out);

  integer t;

  initial begin
    for (t = -10; t < 30; t = t + 1) begin
      #1
      i1 <= t;
      $display("i1 = %d, o1 = %d", i1, o1);

      assign k5 = k4 ? k4 : o1;
      assign k4 = k3 ? k3 : o1;
      assign k3 = k2 ? k2 : o1;
      assign k2 = k1 ? k1 : o1;
      assign k1 = o1;

      $display("out = %d", out);

      $moniter($time, "i1 = %d, o1 = %d, o2 = %d, out = %d k1 = %d, k2 = %d, k3 = %d, k4 = %d, k5 = %d", i1, o1, o2, out, k1, k2, k3, k4, k5);
    end
  end
endmodule

I'd bet that there are other errors in my program too, so any help is much appreciated.

Upvotes: 1

Views: 4624

Answers (1)

Oldfart
Oldfart

Reputation: 6259

As mentioned in the comments:

Remove the always and keep the output [11:0] out
or
Change to:

reg [11:0] o2;
reg [11:0] out;
always @( * )
begin
  o2 = (k1 + k2 + k3 + k4 + k5) / 5;
  out = o2;
end

Second error: Your port uses k1, k2, k3, k3, k4 and is missing k5.

Thirdly: please don't use the port style from last century. I advise you to switch to the new format:

module moving_average(
  input k1, k2, k3, k4, k5,
  output signed [11:0] o2,out
);

Or for the second case: output signed reg [11:0] o2,out

Fourth: it is $monitor, not $moniter

Upvotes: 2

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