Question

I’m making a reaction timer. I have made the individual modules before, and now all that remains is to use them collectively.

In other languages they are used as functions that return a value. Here I understand that modules are instantiated. I know how to instantiate as I have done for the LFSR, but for the LED multiplexer, I don’t know how to.

Here is my LFSR code that will be instantiated into the main module:

module LFSR(
    input clock,
    input reset,
    output [29:0] rnd
    );

wire feedback = rnd[29] ^ rnd[5] ^ rnd[3] ^ rnd[0]; 

reg [29:0] random;

always @ (posedge clock or posedge reset)
begin
    if (reset)
        random <= 30'hF;
    else
        random <= {random[28:0], feedback};
end

assign rnd = random;

endmodule

And here is the main module. At places I have to call the LED circuit to display “Hi” and then later to display the stop watch. Ive marked them with comments.. How can i do that?

module reaction(
    input clock,
    input reset,
    input start,
    input stop,
    output a,
    output b,
    output c,
    output d,
    output e,
    output f,
    output g,
    output h,
    output dp,
    output led
    );

reg [29:0] random;

LFSR random_gen(.clock(clock), .reset(reset), .rnd(random));

localparam [1:0]
                        idle = 2'b00,
                        start = 2'b01,
                        time_it = 2'b10,
                        stop = 2'b11;

reg state_reg, state_next;
reg [29:0] count_reg, count_next;

always @ (posedge clock or posedge reset)
begin
    if(reset)
        begin 
            state_reg <= idle;
            count_reg <= 0;
        end
    else
        state_reg <= state_next;
        count_reg <= count_next;
end

always @ (*)
begin
    state_next = state_reg; //default state stays the same
    count_next = count_reg;

    case(state_reg)
        idle:
                //"DISPLAY HI HERE .......... HOW??
                if(start)
                begin
                    count_next = random;
                    state_next = start;
                end

        start:
                if(count_next == 750000000) // 750M equals a delay of 15 seconds.
                begin
                    led = 1'b1;
                    state_next = time_it;
                end

                else
                    count_next = count_reg + 1;

        time_it:
                    //START STOPWATCH????????

Now I have already made a working stopwatch. Its written below:

module stopwatch(
    input clock,
    input reset,
    input start,
    output a, b, c, d, e, f, g, dp,
    output [3:0] an
    );

reg [3:0] reg_d0, reg_d1, reg_d2, reg_d3; //registers that will hold the individual counts
reg [22:0] ticker; //23 bits needed to count up to 5M bits
wire click;


//the mod 5M clock to generate a tick ever 0.1 second

always @ (posedge clock or posedge reset)
begin
    if(reset)

        ticker <= 0;

    else if(ticker == 5000000) //if it reaches the desired max value reset it
        ticker <= 0;
    else if(start) //only start if the input is set high
        ticker <= ticker + 1;
end

assign click = ((ticker == 5000000)?1'b1:1'b0); //click to be assigned high every 0.1 second

always @ (posedge clock or posedge reset)
begin
    if (reset)
        begin
            reg_d0 <= 0;
            reg_d1 <= 0;
            reg_d2 <= 0;
            reg_d3 <= 0;
        end

    else if (click) //increment at every click
        begin
            if(reg_d0 == 9) //xxx9 - the 0.1 second digit
            begin  //if_1
                reg_d0 <= 0;

                if (reg_d1 == 9) //xx99 
                begin  // if_2
                    reg_d1 <= 0;
                    if (reg_d2 == 5) //x599 - the two digit seconds digits
                    begin //if_3
                        reg_d2 <= 0;
                        if(reg_d3 == 9) //9599 - The minute digit
                            reg_d3 <= 0;
                        else
                            reg_d3 <= reg_d3 + 1;
                    end
                    else //else_3
                        reg_d2 <= reg_d2 + 1;
                end

                else //else_2
                    reg_d1 <= reg_d1 + 1;
            end 

            else //else_1
                reg_d0 <= reg_d0 + 1;
        end
end

//The Circuit for Multiplexing - Look at my other post for details on this

localparam N = 18;

reg [N-1:0]count;

always @ (posedge clock or posedge reset)
    begin
        if (reset)
            count <= 0;
        else
            count <= count + 1;
    end

reg [6:0]sseg;
reg [3:0]an_temp;
reg reg_dp;
always @ (*)
    begin
        case(count[N-1:N-2])

            2'b00 : 
                begin
                    sseg = reg_d0;
                    an_temp = 4'b1110;
                    reg_dp = 1'b1;
                end

            2'b01:
                begin
                    sseg = reg_d1;
                    an_temp = 4'b1101;
                    reg_dp = 1'b0;
                end

            2'b10:
                begin
                    sseg = reg_d2;
                    an_temp = 4'b1011;
                    reg_dp = 1'b1;
                end

            2'b11:
                begin
                    sseg = reg_d3;
                    an_temp = 4'b0111;
                    reg_dp = 1'b0;
                end
        endcase
    end
assign an = an_temp;

reg [6:0] sseg_temp;    
always @ (*)
    begin
        case(sseg)
            4'd0 : sseg_temp = 7'b1000000;
            4'd1 : sseg_temp = 7'b1111001;
            4'd2 : sseg_temp = 7'b0100100;
            4'd3 : sseg_temp = 7'b0110000;
            4'd4 : sseg_temp = 7'b0011001;
            4'd5 : sseg_temp = 7'b0010010;
            4'd6 : sseg_temp = 7'b0000010;
            4'd7 : sseg_temp = 7'b1111000;
            4'd8 : sseg_temp = 7'b0000000;
            4'd9 : sseg_temp = 7'b0010000;
            default : sseg_temp = 7'b0111111; //dash
        endcase
    end
assign {g, f, e, d, c, b, a} = sseg_temp;   
assign dp = reg_dp;


endmodule

I hope I have been able to explain my problem.

Thank you for reading

Updated code:

module reaction(
    input clock,
    input reset,
    input start,
    input stop,
    output a,
    output b,
    output c,
    output d,
    output e,
    output f,
    output g,
    output dp,
     output [3:0] an,
    output reg led
    );

wire [29:0] random;
reg go_hi, go_start;

//instantiate the random number generator
LFSR random_gen(.clock(clock), .reset(reset), .rnd(random));

//inistantiate module to display hi
say_hi sayhi(.clock(clock), .reset(reset), .go(go_hi), .a(a), .b(b), .c(c), .d(d), 
                    .e(e), .f(f), .g(g), .dp(dp), .an(an));

//instantiate the millisecond timer
stopwatch timer(.clock(clock), .reset(reset), .start(go_start), .a(a), .b(b), .c(c), .d(d), 
                    .e(e), .f(f), .g(g), .dp(dp), .an(an));

localparam [1:0]
                        idle = 2'b00,
                        starting = 2'b01,
                        time_it = 2'b10;
                        //stop = 2'b11;

reg state_reg, state_next;
reg [29:0] count_reg, count_next;

always @ (posedge clock or posedge reset)
begin
    if(reset)
        begin 
            state_reg <= idle;
            count_reg <= 0;
        end
    else
        state_reg <= state_next;
        count_reg <= count_next;
end

always @ (*)
begin
    state_next = state_reg; //default state stays the same
    count_next = count_reg;

    case(state_reg)
        idle:
            begin
                //DISPLAY HI HERE
                go_hi = 1;
                if(start)
                begin
                    go_hi = 0;  //dont display hi anymore
                    count_next = random;
                    state_next = starting;
                end
            end
        starting:
            begin
                if(count_next == 750) // 750M equals a delay of 15 seconds.
                begin                           //and starting from 'rand' ensures a random delay
                    led = 1'b1;
                    state_next = time_it;
                end

                else
                    count_next = count_reg + 1;
            end     
        time_it:
            begin
                    go_start = 1;
                    if(stop)
                        go_start = 0;
            end

        endcase

end

endmodule

Answer 1

At places I have to call the LED circuit to display “Hi” and then later to display the stop watch. Ive marked them with comments.. How can i do that?

If you want to understand verilog you have to break the idea that you ‘call’ a module. Modules don’t exist just when you want them to. In your case, you need to instantiate a stopwatch module, and connect the ports up (the line below the LFSR instantiation might be an appropriate place to do this).

When you do this, realize that your stopwatch is always driving the output LED, not just during certain states. If you want to change the display mode (to display a string like Hi, or to display the stopwatch time), you should have an input to your stopwatch module telling it what it should display.

Perhaps an input like display_mode could be used, where 2’d0 means display “hi”, 2’d1 means display stopwatch time, 2’d2 means display dancing pattern, etc.

At appropriate points in your main reaction module, you could then change the value of display_mode, which will then change what stopwatch drives back out.