Conway's Game of Life in Verilog

GoL.v

/*
	Conway's Game of Life modeled in Verilog by Adam Thomas / devdsp
*/

/*
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * <github.com/devdsp> wrote this file. As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return. - Adam
 * ----------------------------------------------------------------------------
 */

module count_neighbours (neighbours,sum);
    input [7:0] neighbours;
    output [3:0] sum;

    wire [3:0] sum;

    assign sum = neighbours[7] + 
                 neighbours[6] +
                 neighbours[5] +
                 neighbours[4] +
                 neighbours[3] +
                 neighbours[2] +
                 neighbours[1] +
                 neighbours[0];
endmodule

module rules (pop_count, current_state, next_state);
    input [3:0] pop_count;
    input current_state;
    output next_state;
    wire next_state;

    assign next_state = (pop_count == 2 & current_state) | pop_count == 3;
endmodule    	

module gol_cell( neighbours, clk, rst, seed, state );
    input [7:0] neighbours;
    input clk;
    input rst;
    input seed;
    output state;

    wire [3:0] pop;
    wire next_state;

    reg state;

    count_neighbours cn(neighbours, pop);
    rules r(pop, state, next_state);

    always @(posedge clk or negedge rst) begin
        if(~rst) begin
            state = seed;
        end else begin
            state = next_state;
        end
    end
endmodule


module gol_cel_tb;

    reg [7:0] neighbours;
    reg clk;
    reg rst;
    reg seed;
    wire state;

    initial begin
	$dumpfile("gol.vcd");
        $dumpvars(0, top);
        neighbours = 0;
        clk = 0;
        rst = 1;
        seed = 0;

        #5 rst = 0;
        #15 rst = 1;
        #10 neighbours = 8'b00000000;
        #10 neighbours = 8'b00000100;
        #10 neighbours = 8'b00010010;
        #10 neighbours = 8'b01100100;
        #10 neighbours = 8'b00100100;
        #10 neighbours = 8'b00000000;
        #10 neighbours = 8'b00110100;
        #10 neighbours = 8'b00111100;
        #10 neighbours = 8'b00101000;
        #10 seed = 1;
        #10 rst = 0;
        #10 rst = 1;
        #10 neighbours = 8'b00110100;
        #10 neighbours = 8'b00101000;
        #10 neighbours = 8'b00000000;


        #10 $finish;
    end

    always begin
        #5 clk = ! clk;
    end

    gol_cell top( neighbours, clk, rst, seed, state );
endmodule