module stopwatch(
    input clock,
    input reset,
    input start,
    output [6:0]hex0,
    output [6:0]hex1,
    output [6:0]hex2,
    output [6:0]hex3
    );

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 == 50000000) //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 == 50000000)?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

reg [6:0]hex0_temp;
reg [6:0]hex1_temp;
reg [6:0]hex2_temp;
reg [6:0]hex3_temp;

always @ (*)
 begin
  case(reg_d0)
   4'd0 : hex0_temp = 7'b0111111;
   4'd1 : hex0_temp = 7'b0000110;
   4'd2 : hex0_temp = 7'b1011011;
   4'd3 : hex0_temp = 7'b1001111;
   4'd4 : hex0_temp = 7'b1100110;
   4'd5 : hex0_temp = 7'b1101101;
   4'd6 : hex0_temp = 7'b1111101;
   4'd7 : hex0_temp = 7'b0000111;
   4'd8 : hex0_temp = 7'b1111111;
   4'd9 : hex0_temp = 7'b1101111;
   default : hex0_temp = 7'b1000000; //dash
  endcase
  case(reg_d1)
   4'd0 : hex1_temp = 7'b0111111;
   4'd1 : hex1_temp = 7'b0000110;
   4'd2 : hex1_temp = 7'b1011011;
   4'd3 : hex1_temp = 7'b1001111;
   4'd4 : hex1_temp = 7'b1100110;
   4'd5 : hex1_temp = 7'b1101101;
   4'd6 : hex1_temp = 7'b1111101;
   4'd7 : hex1_temp = 7'b0000111;
   4'd8 : hex1_temp = 7'b1111111;
   4'd9 : hex1_temp = 7'b1101111;
   default : hex1_temp = 7'b1000000; //dash
  endcase
  case(reg_d2)
   4'd0 : hex2_temp = 7'b0111111;
   4'd1 : hex2_temp = 7'b0000110;
   4'd2 : hex2_temp = 7'b1011011;
   4'd3 : hex2_temp = 7'b1001111;
   4'd4 : hex2_temp = 7'b1100110;
   4'd5 : hex2_temp = 7'b1101101;
   4'd6 : hex2_temp = 7'b1111101;
   4'd7 : hex2_temp = 7'b0000111;
   4'd8 : hex2_temp = 7'b1111111;
   4'd9 : hex2_temp = 7'b1101111;
   default : hex2_temp = 7'b1000000; //dash
  endcase
  case(reg_d3)
   4'd0 : hex3_temp = 7'b0111111;
   4'd1 : hex3_temp = 7'b0000110;
   4'd2 : hex3_temp = 7'b1011011;
   4'd3 : hex3_temp = 7'b1001111;
   4'd4 : hex3_temp = 7'b1100110;
   4'd5 : hex3_temp = 7'b1101101;
   4'd6 : hex3_temp = 7'b1111101;
   4'd7 : hex3_temp = 7'b0000111;
   4'd8 : hex3_temp = 7'b1111111;
   4'd9 : hex3_temp = 7'b1101111;
   default : hex3_temp = 7'b1000000; //dash
  endcase
 end

assign hex0 = hex0_temp;
assign hex1 = hex1_temp;
assign hex2 = hex2_temp;
assign hex3 = hex3_temp;

endmodule