verilog阻塞与非阻塞的初步理解(二)

将阻塞模块改为下述代码：

module blocking(clk,a,b,c);
  input[3:0] a;
  input clk;
  output[3:0] b,c;
reg[3:0] b,c;

always @(posedge clk)
    begin
      c=b;
     $display("blocking:a=%d,b=%d,c=%d.",a,b,c);
    end

always @(posedge clk)
    begin
      b=a;
      $display("blocking:a=%d,b=%d,c=%d.",a,b,c);
    end
    
endmodule
 

仿真得出结果：

# ________________
# blocking:a= 3,b= x,c= x.
# blocking:a= 3,b= x,c= x.
# non_blocking:a= 3,b= x,c= x.
# ________________
# blocking:a= 7,b= 3,c= x.
# blocking:a= 7,b= 3,c= x.
# non_blocking:a= 7,b= 3,c= x.
# ________________
# blocking:a=15,b= 7,c= 3.
# blocking:a=15,b= 7,c= 3.
# non_blocking:a=15,b= 7,c= 3.
# ________________
# blocking:a=10,b=15,c= 7.
# blocking:a=10,b=15,c= 7.
# non_blocking:a=10,b=15,c= 7.
# ________________
# blocking:a= 2,b=10,c=15.
# blocking:a= 2,b=10,c=15.
# non_blocking:a= 2,b=10,c=15.

若更改两个always 模块的先后顺序如下：

 

module blocking(clk,a,b,c);
  input[3:0] a;
  input clk;
  output[3:0] b,c;
reg[3:0] b,c;


always @(posedge clk)
    begin
      b=a;
      $display("blocking:a=%d,b=%d,c=%d.",a,b,c);
    end
    
always @(posedge clk)
    begin
      c=b;
     $display("blocking:a=%d,b=%d,c=%d.",a,b,c);
    end

    
endmodule

 

 

 

则会得到结果：

# ________________
# blocking:a= 3,b= 3,c= x.
# blocking:a= 3,b= 3,c= 3.
# non_blocking:a= 3,b= x,c= x.
# ________________
# blocking:a= 7,b= 7,c= 3.
# blocking:a= 7,b= 7,c= 7.
# non_blocking:a= 7,b= 3,c= x.
# ________________
# blocking:a=15,b=15,c= 7.
# blocking:a=15,b=15,c=15.
# non_blocking:a=15,b= 7,c= 3.
# ________________
# blocking:a=10,b=10,c=15.
# blocking:a=10,b=10,c=10.
# non_blocking:a=10,b=15,c= 7.
# ________________
# blocking:a= 2,b= 2,c=10.
# blocking:a= 2,b= 2,c= 2.
# non_blocking:a= 2,b=10,c=15.

可以看出alway模块的先后顺序会影响b,c的取值。理论上，两个模块是并行执行的，他们出现的先后顺序并不会影响最终得到的结果。

但从这里看出，其是有先后顺序的。只是不知道是仿真器的顺序执行的原因还是竞争冒险导致的。

不过这种情况在非阻塞赋值时不会出现，非阻塞赋值结果是一致的。