Changing Counter target according to input

Question

I'm working on a project for a digital design course, and I have to play musical notes using frequencies in my project. I must say I'm fairly inexperienced in verilog (have to use verilog for the project). I researched a bit regarding the topic and found (here) the following code snippet:

    module music(clk, speaker);
    input clk;
    output speaker;
    parameter clkdivider = 25000000/440/2;

    reg [14:0] counter;
    always @(posedge clk) if(counter==0) counter <= clkdivider-1; else counter <= counter-1;

    reg speaker;
    always @(posedge clk) if(counter==0) speaker <= ~speaker;
    endmodule

In this code the clock is 25MHz and the frequency of the output is 440, what I want to do is change the frequency of the output according to user input, so I assume I just have to change the value the counter counts to. How can I neatly add that to the code so it should work ?

Answer 1

To get you started, I've set-up an environment for you. You must add you're logic to make the correct functionality (homework) especially in counter register where in you have to calculate the required frequency.

          // change logic here (to add userinput)
            counter <= clkdivider-1; 

Since you want to change the frequency of the output according to user input, you should add an input port to the music module.

module music(clk, reset, userinput, valid, speaker);
    input clk, valid, reset;
    input [7:0] userinput;
    output speaker;

userinput is 8 bits but you can change this based from your requirements. Take note that a valid signal is also needed for handshaking with the other modules.

Reset is also added to clear your music module.

Here is your testbench

module testmusic;
reg clk;
reg [7:0] userinput;
wire speaker;
reg valid;
 reg reset;


initial begin
  forever begin
    #1 clk = !clk;
  end
end

initial begin
  clk = 0;
  userinput = 0;
  valid = 0;
  @(posedge clk);
  $monitor("userinput: %0h valid: %0h speaker: %0h\n", userinput, valid, speaker);
end


 task resetdut;
   reset = 0;

   repeat (3) begin
    @(posedge clk);
   end

   reset <= 1;

   repeat (3) begin
    @(posedge clk);
   end

   reset <= 0;
 endtask

 music dut(clk, reset, userinput, valid, speaker);

 initial begin
   #10000; $finish;
 end

 // perform our testing here
 initial begin
   // perform reset to initialize our dut
   resetdut;
   testuserinput;
 end

 task testuserinput;
   @(posedge clk);
   userinput <= 8'hF; // insert user input here
   valid <= 1;
   @(posedge clk);
   userinput <= 0;
   valid <= 0;
   @(posedge clk);
 endtask


endmodule

Here is your RTL code that you need to fix.

module music(clk, reset, userinput, valid, speaker);
    input clk, valid, reset;
    input [7:0] userinput;
    output speaker;
    parameter clkdivider = 25000000/440/2;

    reg [14:0] counter;

  reg [7:0] reginput;

    always @(posedge clk) begin
      if (reset) begin
        counter <= 0;
      end
      else begin
        if(counter==0) begin
          // change logic here (to add userinput)
            counter <= clkdivider-1; 
        end
        else begin
            counter <= counter-1;
        end
      end
    end

    reg speaker;
    always @(posedge clk) begin
      if (reset) begin
        speaker <= 0;
      end
      else begin
        if(counter==0) begin
            speaker <= ~speaker;
        end
      end
    end

    // handshake
  always @(posedge clk) begin
    if (reset) begin
      reginput <= 0;
    end
    else begin
        if (valid) begin
          reginput <= userinput;
        end
    end
  end

endmodule

You may want to compile the code here http://www.edaplayground.com/x/PR2