Program Block-systemverilog

systemverilog中的Program Block与module有些类似，但module是基于硬件思想，Program Block纯粹是为了仿真。如果不熟悉program,可以不用program.

The program block serves three basic purposes:

• » It provides an entry point to the execution of testbenches.
• » It creates a scope that encapsulates program-wide data.
• » It provides a syntactic context that specifies scheduling in the Reactive region.

module test(...) int shared; // variable shared by programs p1 and p1
program p1; ...
endprogram
program p2;
...
endprogram // p1 and p2 are implicitly instantiated once in module testendmodule

1.   `timescale 1ns/1ps
2.    
3.   class frame_start;
4.   rand byte length = 64'habcdabc101023acd123;
5.   rand byte tag_frame_ma;
6.   byte Num;//octal number
7.   integer Tx_en;
8.   task frame();
9.   begin
10.   if ((length/Num) || (length > tag_frame_ma))
11.   $display ("\nReport the Tag frame error length = %d",length);
12.   else
13.   $display("\nReport Tag frame %d",length);
14.   end
15.   endtask
16.   endclass
17.    
18.   program sim_top();
19.   frame_start new_frame;
20.   integer transmission_enable = 0;// Transmission of frame. Frame Tx include data encapulation and Media Access Management
21.   task transmit(integer transmission_enable);
22.   if (transmission_enable)
23.   $display("\n@%g, Frame is ready to transmit",$time);
24.   else
25.   $display("\n@%g, Frame is not ready now to transmit",$time);
26.   endtask
27.   initial
28.   begin
29.   new_frame = new;
30.   $display("*******--------*********--------********--------********");
31.   #1 transmit(transmission_enable);
32.   #1 transmission_enable = 1;
33.   #1 transmit(transmission_enable);
34.   #1 new_frame.frame();
35.   #1 new_frame.randomize();
36.   #1 $display("\n@%g, Transmit next frame now...", $time);
37.   #1 $display("\n*******--------*********--------********--------********");
38.   end
39.   endprogram

1.   # *******--------*********--------********--------********
2.   #
3.   # @1, Frame is not ready now to transmit
4.   #
5.   # @3, Frame is ready to transmit
6.   #
7.   # Report the Tag frame error length = 35
8.   #
9.   # @6, Transmit next frame now...
10.   #
11.   # *******--------*********--------********--------********