原创 modelsim功能仿真正确，时序仿真没有输出

源文件和测试文件如下：请大家给出解决办法

module pipeline_add(a,b,cin,cout,sum,clk);
input[3:0] a,b;
input clk,cin;
output[3:0]sum;
output cout;
reg[3:0] tempa,tempb;
reg tempci;
reg cout;
reg firstco;
reg[1:0] firstsum;
reg[2:0] firsta,firstb;          //??3?fista[2]?￠firstn[2]·?????
reg[3:0] sum;
always@(posedge clk)
   begin
      tempa="a";                 //ê?è?êy?Y?o′?
      tempb="b";
      tempci="cin";
   end
always@(posedge clk)
   begin
  {firstco,firstsum}=tempa[1:0]+tempb[1:0]+tempci;  //μúò????ó￡¨μí2??￡?
       firsta="tempa"[3:2];                   //?′2??ó????μ?êy?Y?o′?
       firstb="tempb"[3:2];
   end
always@(posedge clk)
   begin
 {cout,sum}={firsta[2:0]+firstb[2:0]+firstco,firstsum}; //μú?t???ó￡¨??2??￡?
   end
endmodule

`timescale 1ns/1ps
module pipeline_add_test;
    reg [3:0] a = 4'b0000;
    reg [3:0] b = 4'b0000;
    reg cin = 1'b0;
    wire cout;
    wire [3:0] sum;
    reg clk = 1'b0;
    parameter PERIOD = 200;
    parameter real DUTY_CYCLE = 0.5;
    parameter OFFSET = 100;
initial    // Clock process for clk
    begin
        #OFFSET;
        forever
        begin
            clk = 1'b0;
            #(PERIOD-(PERIOD*DUTY_CYCLE)) clk = 1'b1;
            #(PERIOD*DUTY_CYCLE);
        end
    end
    pipeline_add UUT (
        .a(a),
        .b(b),
        .cin(cin),
        .cout(cout),
        .sum(sum),
        .clk(clk));
initial begin
        // -------------  Current Time:  100ns
        #100;
        cin = 1'b1;
        // -------------------------------------
        // -------------  Current Time:  185ns
        #85;
        a = 4'b0010;
        b = 4'b0011;
        // -------------------------------------
        // -------------  Current Time:  385ns
        #200;
        a = 4'b0100;
        b = 4'b0010;
        // -------------------------------------
        // -------------  Current Time:  585ns
        #200;
        cin = 1'b0;
        a = 4'b1010;
        b = 4'b0011;
// -------------------------------------
        // -------------  Current Time:  785ns
        #200;
        a = 4'b1011;
        b = 4'b1010;
        // -------------------------------------
        // -------------  Current Time:  985ns
        #200;
        a = 4'b1111;
        b = 4'b1110;
        // -------------------------------------
        // -------------  Current Time:  1185ns
        #200;
        a = 4'b1101;
        b = 4'b0100;
// -------------------------------------
        // -------------  Current Time:  1585ns
        #400;
        a = 4'b0011;
        // -------------------------------------
        // -------------  Current Time:  1785ns
        #200;
        b = 4'b1101;
        // -------------------------------------
        // -------------  Current Time:  1985ns
        #200;
        cin = 1'b1;
        a = 4'b0101;
        b = 4'b1111;
        // -------------------------------------
        // -------------  Current Time:  2385ns
        #400;
        a = 4'b0100;
        b = 4'b1101;
        // -------------------------------------
    end
endmodule