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

Examp:

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

output:

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. # *******--------*********--------********--------********